Documentation / scsi / ncr53c8xx.txt

Based on kernel version 2.6.26. Page generated on 2008-07-16 21:13 EST.

	The Linux NCR53C8XX/SYM53C8XX drivers README file
	
	Written by Gerard Roudier <groudier[AT]free[DOT]fr>
	21 Rue Carnot
	95170 DEUIL LA BARRE - FRANCE
	
	29 May 1999
	===============================================================================
	
	1.  Introduction
	2.  Supported chips and SCSI features
	3.  Advantages of the enhanced 896 driver
	      3.1 Optimized SCSI SCRIPTS
	      3.2 New features of the SYM53C896 (64 bit PCI dual LVD SCSI controller)
	4.  Memory mapped I/O versus normal I/O
	5.  Tagged command queueing
	6.  Parity checking
	7.  Profiling information
	8.  Control commands
	      8.1  Set minimum synchronous period
	      8.2  Set wide size
	      8.3  Set maximum number of concurrent tagged commands
	      8.4  Set order type for tagged command
	      8.5  Set debug mode
	      8.6  Clear profile counters
	      8.7  Set flag (no_disc)
	      8.8  Set verbose level
	      8.9  Reset all logical units of a target
	      8.10 Abort all tasks of all logical units of a target
	9.  Configuration parameters
	10. Boot setup commands
	      10.1 Syntax
	      10.2 Available arguments
	             10.2.1  Master parity checking
	             10.2.2  Scsi parity checking
	             10.2.3  Scsi disconnections
	             10.2.4  Special features
	             10.2.5  Ultra SCSI support
	             10.2.6  Default number of tagged commands
	             10.2.7  Default synchronous period factor
	             10.2.8  Negotiate synchronous with all devices
	             10.2.9  Verbosity level
	             10.2.10 Debug mode
	             10.2.11 Burst max
	             10.2.12 LED support
	             10.2.13 Max wide
	             10.2.14 Differential mode
	             10.2.15 IRQ mode
	             10.2.16 Reverse probe
	             10.2.17 Fix up PCI configuration space
	             10.2.18 Serial NVRAM
	             10.2.19 Check SCSI BUS 
	             10.2.20 Exclude a host from being attached
	             10.2.21 Suggest a default SCSI id for hosts
	             10.2.22 Enable use of IMMEDIATE ARBITRATION
	      10.3 Advised boot setup commands
	      10.4 PCI configuration fix-up boot option
	      10.5 Serial NVRAM support boot option
	      10.6 SCSI BUS checking boot option
	      10.7 IMMEDIATE ARBITRATION boot option
	11. Some constants and flags of the ncr53c8xx.h header file
	12. Installation
	13. Architecture dependent features
	14. Known problems
	      14.1 Tagged commands with Iomega Jaz device
	      14.2 Device names change when another controller is added
	      14.3 Using only 8 bit devices with a WIDE SCSI controller.
	      14.4 Possible data corruption during a Memory Write and Invalidate
	      14.5 IRQ sharing problems
	15. SCSI problem troubleshooting
	      15.1 Problem tracking
	      15.2 Understanding hardware error reports
	16. Synchronous transfer negotiation tables
	      16.1 Synchronous timings for 53C875 and 53C860 Ultra-SCSI controllers
	      16.2 Synchronous timings for fast SCSI-2 53C8XX controllers
	17. Serial NVRAM support (by Richard Waltham)
	      17.1 Features
	      17.2 Symbios NVRAM layout
	      17.3 Tekram  NVRAM layout
	18. Support for Big Endian
	      18.1 Big Endian CPU
	      18.2 NCR chip in Big Endian mode of operations
	
	===============================================================================
	
	1. Introduction
	
	The initial Linux ncr53c8xx driver has been a port of the ncr driver from 
	FreeBSD that has been achieved in November 1995 by:
	          Gerard Roudier              <groudier[AT]free[DOT]fr>
	
	The original driver has been written for 386bsd and FreeBSD by:
	          Wolfgang Stanglmeier        <wolf[AT]cologne[DOT]de>
	          Stefan Esser                <se[AT]mi.Uni-Koeln[DOT]de>
	
	It is now available as a bundle of 2 drivers:
	
	- ncr53c8xx generic driver that supports all the SYM53C8XX family including 
	  the earliest 810 rev. 1, the latest 896 (2 channel LVD SCSI controller) and
	  the new 895A (1 channel LVD SCSI controller).
	- sym53c8xx enhanced driver (a.k.a. 896 drivers) that drops support of oldest 
	  chips in order to gain advantage of new features, as LOAD/STORE instructions 
	  available since the 810A and hardware phase mismatch available with the 
	  896 and the 895A.
	
	You can find technical information about the NCR 8xx family in the
	PCI-HOWTO written by Michael Will and in the SCSI-HOWTO written by
	Drew Eckhardt.
	
	Information about new chips is available at LSILOGIC web server:
	
	          http://www.lsilogic.com/
	
	SCSI standard documentations are available at SYMBIOS ftp server:
	
	          ftp://ftp.symbios.com/
	
	Useful SCSI tools written by Eric Youngdale are available at tsx-11:
	
	          ftp://tsx-11.mit.edu/pub/linux/ALPHA/scsi/scsiinfo-X.Y.tar.gz
	          ftp://tsx-11.mit.edu/pub/linux/ALPHA/scsi/scsidev-X.Y.tar.gz
	
	These tools are not ALPHA but quite clean and work quite well.
	It is essential you have the 'scsiinfo' package.
	
	This short documentation describes the features of the generic and enhanced
	drivers, configuration parameters and control commands available through 
	the proc SCSI file system read / write operations.
	
	This driver has been tested OK with linux/i386, Linux/Alpha and Linux/PPC.
	
	Latest driver version and patches are available at:
	
	          ftp://ftp.tux.org/pub/people/gerard-roudier
	or
	          ftp://ftp.symbios.com/mirror/ftp.tux.org/pub/tux/roudier/drivers
	
	I am not a native speaker of English and there are probably lots of
	mistakes in this README file. Any help will be welcome.
	
	
	2. Supported chips and SCSI features
	
	The following features are supported for all chips:
	
		Synchronous negotiation
		Disconnection
		Tagged command queuing
		SCSI parity checking
		Master parity checking
	
	"Wide negotiation" is supported for chips that allow it.  The
	following table shows some characteristics of NCR 8xx family chips 
	and what drivers support them.
	
	                                                  Supported by   Supported by
	       On board                                   the generic    the enhanced 
	Chip   SDMS BIOS   Wide   SCSI std.   Max. sync   driver         driver
	----   ---------   ----   ---------   ----------  ------------   -------------
	810        N         N      FAST10    10 MB/s        Y             N
	810A       N         N      FAST10    10 MB/s        Y             Y
	815        Y         N      FAST10    10 MB/s        Y             N
	825        Y         Y      FAST10    20 MB/s        Y             N
	825A       Y         Y      FAST10    20 MB/s        Y             Y
	860        N         N      FAST20    20 MB/s        Y             Y
	875        Y         Y      FAST20    40 MB/s        Y             Y
	876        Y         Y      FAST20    40 MB/s        Y             Y
	895        Y         Y      FAST40    80 MB/s        Y             Y
	895A       Y         Y      FAST40    80 MB/s        Y             Y
	896        Y         Y      FAST40    80 MB/s        Y             Y
	897        Y         Y      FAST40    80 MB/s        Y             Y
	1510D      Y         Y      FAST40    80 MB/s        Y             Y
	1010       Y         Y      FAST80   160 MB/s        N             Y
	1010_66*   Y         Y      FAST80   160 MB/s        N             Y
	
	* Chip supports 33MHz and 66MHz PCI buses.
	
	
	Summary of other supported features:
	
	Module:                allow to load the driver
	Memory mapped I/O:     increases performance
	Profiling information: read operations from the proc SCSI file system
	Control commands:      write operations to the proc SCSI file system
	Debugging information: written to syslog (expert only)
	Scatter / gather
	Shared interrupt
	Boot setup commands
	Serial NVRAM:          Symbios and Tekram formats
	
	
	3. Advantages of the enhanced 896 driver
	
	3.1 Optimized SCSI SCRIPTS.
	
	The 810A, 825A, 875, 895, 896 and 895A support new SCSI SCRIPTS instructions 
	named LOAD and STORE that allow to move up to 1 DWORD from/to an IO register 
	to/from memory much faster that the MOVE MEMORY instruction that is supported 
	by the 53c7xx and 53c8xx family.
	The LOAD/STORE instructions support absolute and DSA relative addressing 
	modes.  The SCSI SCRIPTS had been entirely rewritten using LOAD/STORE instead 
	of MOVE MEMORY instructions.
	
	3.2 New features of the SYM53C896 (64 bit PCI dual LVD SCSI controller)
	
	The 896 and the 895A allows handling of the phase mismatch context from 
	SCRIPTS (avoids the phase mismatch interrupt that stops the SCSI processor 
	until the C code has saved the context of the transfer).
	Implementing this without using LOAD/STORE instructions would be painfull 
	and I didn't even want to try it.
	
	The 896 chip supports 64 bit PCI transactions and addressing, while the 
	895A supports 32 bit PCI transactions and 64 bit addressing.
	The SCRIPTS processor of these chips is not true 64 bit, but uses segment 
	registers for bit 32-63. Another interesting feature is that LOAD/STORE 
	instructions that address the on-chip RAM (8k) remain internal to the chip.
	
	Due to the use of LOAD/STORE SCRIPTS instructions, this driver does not 
	support the following chips:
	- SYM53C810 revision < 0x10 (16)
	- SYM53C815 all revisions
	- SYM53C825 revision < 0x10 (16)
	
	4. Memory mapped I/O versus normal I/O
	
	Memory mapped I/O has less latency than normal I/O.  Since
	linux-1.3.x, memory mapped I/O is used rather than normal I/O.  Memory
	mapped I/O seems to work fine on most hardware configurations, but
	some poorly designed motherboards may break this feature.
	
	The configuration option CONFIG_SCSI_NCR53C8XX_IOMAPPED forces the
	driver to use normal I/O in all cases.
	
	
	5. Tagged command queueing
	
	Queuing more than 1 command at a time to a device allows it to perform 
	optimizations based on actual head positions and its mechanical 
	characteristics. This feature may also reduce average command latency.
	In order to really gain advantage of this feature, devices must have 
	a reasonable cache size (No miracle is to be expected for a low-end 
	hard disk with 128 KB or less).
	Some kown SCSI devices do not properly support tagged command queuing.
	Generally, firmware revisions that fix this kind of problems are available 
	at respective vendor web/ftp sites.
	All I can say is that the hard disks I use on my machines behave well with 
	this driver with tagged command queuing enabled:
	
	- IBM S12 0662
	- Conner 1080S
	- Quantum Atlas I
	- Quantum Atlas II
	
	If your controller has NVRAM, you can configure this feature per target 
	from the user setup tool. The Tekram Setup program allows to tune the 
	maximum number of queued commands up to 32. The Symbios Setup only allows 
	to enable or disable this feature.
	
	The maximum number of simultaneous tagged commands queued to a device
	is currently set to 8 by default.  This value is suitable for most SCSI
	disks.  With large SCSI disks (>= 2GB, cache >= 512KB, average seek time
	<= 10 ms), using a larger value may give better performances.
	
	The sym53c8xx driver supports up to 255 commands per device, and the 
	generic ncr53c8xx driver supports up to 64, but using more than 32 is 
	generally not worth-while, unless you are using a very large disk or disk 
	array. It is noticeable that most of recent hard disks seem not to accept 
	more than 64 simultaneous commands. So, using more than 64 queued commands 
	is probably just resource wasting.
	
	If your controller does not have NVRAM or if it is managed by the SDMS 
	BIOS/SETUP, you can configure tagged queueing feature and device queue 
	depths from the boot command-line. For example:
	
	  ncr53c8xx=tags:4/t2t3q15-t4q7/t1u0q32
	
	will set tagged commands queue depths as follow:
	
	- target 2  all luns  on controller 0 --> 15
	- target 3  all luns  on controller 0 --> 15
	- target 4  all luns  on controller 0 -->  7
	- target 1  lun 0     on controller 1 --> 32
	- all other target/lun                -->  4
	
	In some special conditions, some SCSI disk firmwares may return a
	QUEUE FULL status for a SCSI command. This behaviour is managed by the
	driver using the following heuristic:
	
	- Each time a QUEUE FULL status is returned, tagged queue depth is reduced 
	  to the actual number of disconnected commands. 
	
	- Every 1000 successfully completed SCSI commands, if allowed by the
	  current limit, the maximum number of queueable commands is incremented.
	
	Since QUEUE FULL status reception and handling is resource wasting, the 
	driver notifies by default this problem to user by indicating the actual 
	number of commands used and their status, as well as its decision on the 
	device queue depth change.
	The heuristic used by the driver in handling QUEUE FULL ensures that the 
	impact on performances is not too bad. You can get rid of the messages by 
	setting verbose level to zero, as follow:
	
	1st method: boot your system using 'ncr53c8xx=verb:0' option.
	2nd method: apply "setverbose 0" control command to the proc fs entry 
	            corresponding to your controller after boot-up.
	
	6. Parity checking
	
	The driver supports SCSI parity checking and PCI bus master parity
	checking.  These features must be enabled in order to ensure safe data
	transfers.  However, some flawed devices or mother boards will have
	problems with parity. You can disable either PCI parity or SCSI parity 
	checking by entering appropriate options from the boot command line.
	(See 10: Boot setup commands).
	
	7. Profiling information
	
	Profiling information is available through the proc SCSI file system.
	Since gathering profiling information may impact performances, this 
	feature is disabled by default and requires a compilation configuration 
	option to be set to Y.
	
	The device associated with a host has the following pathname:
	
	          /proc/scsi/ncr53c8xx/N     (N=0,1,2 ....)
	
	Generally, only 1 board is used on hardware configuration, and that device is:
	          /proc/scsi/ncr53c8xx/0
	
	However, if the driver has been made as module, the number of the
	hosts is incremented each time the driver is loaded.
	
	In order to display profiling information, just enter:
	
	         cat /proc/scsi/ncr53c8xx/0
	
	and you will get something like the following text:
	
	-------------------------------------------------------
	General information:
	  Chip NCR53C810, device id 0x1, revision id 0x2
	  IO port address 0x6000, IRQ number 10
	  Using memory mapped IO at virtual address 0x282c000
	  Synchronous transfer period 25, max commands per lun 4
	Profiling information:
	  num_trans    = 18014
	  num_kbytes   = 671314
	  num_disc     = 25763
	  num_break    = 1673
	  num_int      = 1685
	  num_fly      = 18038
	  ms_setup     = 4940
	  ms_data      = 369940
	  ms_disc      = 183090
	  ms_post      = 1320
	-------------------------------------------------------
	
	General information is easy to understand. The device ID and the
	revision ID identify the SCSI chip as follows:
	
	Chip    Device id     Revision Id
	----    ---------     -----------
	810       0x1            <  0x10
	810A      0x1            >= 0x10
	815       0x4
	825       0x3            <  0x10
	860       0x6
	825A      0x3            >= 0x10
	875       0xf
	895       0xc
	
	The profiling information is updated upon completion of SCSI commands.
	A data structure is allocated and zeroed when the host adapter is
	attached. So, if the driver is a module, the profile counters are
	cleared each time the driver is loaded.  The "clearprof" command
	allows you to clear these counters at any time.
	
	The following counters are available:
	
	("num" prefix means "number of",
	"ms" means milli-seconds)
	
	num_trans
		Number of completed commands
		Example above: 18014 completed commands
	
	num_kbytes
		Number of kbytes transferred
		Example above: 671 MB transferred
	
	num_disc
		Number of SCSI disconnections
		Example above: 25763 SCSI disconnections
	
	num_break
		number of script interruptions (phase mismatch)
		Example above: 1673 script interruptions
	
	num_int
		Number of interrupts other than "on the fly"
		Example above: 1685 interruptions not "on the fly"
	
	num_fly
		Number of interrupts "on the fly"
		Example above: 18038 interruptions "on the fly"
	
	ms_setup
		Elapsed time for SCSI commands setups
		Example above: 4.94 seconds
	
	ms_data
		Elapsed time for data transfers
		Example above: 369.94 seconds spent for data transfer
	
	ms_disc
		Elapsed time for SCSI disconnections
		Example above: 183.09 seconds spent disconnected
	
	ms_post
		Elapsed time for command post processing
		(time from SCSI status get to command completion call)
		Example above: 1.32 seconds spent for post processing
	
	Due to the 1/100 second tick of the system clock, "ms_post" time may
	be wrong.
	
	In the example above, we got 18038 interrupts "on the fly" and only
	1673 script breaks generally due to disconnections inside a segment 
	of the scatter list.
	
	
	8. Control commands
	
	Control commands can be sent to the driver with write operations to
	the proc SCSI file system. The generic command syntax is the
	following:
	
	      echo "<verb> <parameters>" >/proc/scsi/ncr53c8xx/0
	      (assumes controller number is 0)
	
	Using "all" for "<target>" parameter with the commands below will
	apply to all targets of the SCSI chain (except the controller).
	
	Available commands:
	
	8.1 Set minimum synchronous period factor
	
	    setsync <target> <period factor>
	
	    target:    target number
	    period:    minimum synchronous period.
	               Maximum speed = 1000/(4*period factor) except for special
	               cases below.
	
	    Specify a period of 255, to force asynchronous transfer mode.
	
	      10 means 25 nano-seconds synchronous period
	      11 means 30 nano-seconds synchronous period
	      12 means 50 nano-seconds synchronous period
	
	8.2 Set wide size
	
	    setwide <target> <size>
	
	    target:    target number
	    size:      0=8 bits, 1=16bits
	
	8.3 Set maximum number of concurrent tagged commands
	 
	    settags <target> <tags>
	
	    target:    target number
	    tags:      number of concurrent tagged commands
	               must not be greater than SCSI_NCR_MAX_TAGS (default: 8)
	
	8.4 Set order type for tagged command
	
	    setorder <order>
	
	    order:     3 possible values:
	               simple: use SIMPLE TAG for all operations (read and write)
	               ordered: use ORDERED TAG for all operations
	               default: use default tag type,
	                        SIMPLE  TAG for read  operations
	                        ORDERED TAG for write operations
	
	
	8.5 Set debug mode
	
	    setdebug <list of debug flags>
	
	    Available debug flags:
	        alloc:   print info about memory allocations (ccb, lcb)
	        queue:   print info about insertions into the command start queue
	        result:  print sense data on CHECK CONDITION status
	        scatter: print info about the scatter process
	        scripts: print info about the script binding process
		tiny:    print minimal debugging information
		timing:  print timing information of the NCR chip
		nego:    print information about SCSI negotiations
		phase:   print information on script interruptions
	
	    Use "setdebug" with no argument to reset debug flags.
	
	
	8.6 Clear profile counters
	
	    clearprof
	
	    The profile counters are automatically cleared when the amount of
	    data transferred reaches 1000 GB in order to avoid overflow.
	    The "clearprof" command allows you to clear these counters at any time.
	
	
	8.7 Set flag (no_disc)
	 
	    setflag <target> <flag>
	
	    target:    target number
	
	    For the moment, only one flag is available:
	
	        no_disc:   not allow target to disconnect.
	
	    Do not specify any flag in order to reset the flag. For example:
	    - setflag 4
	      will reset no_disc flag for target 4, so will allow it disconnections.
	    - setflag all
	      will allow disconnection for all devices on the SCSI bus.
	
	
	8.8 Set verbose level
	
	    setverbose #level
	
	    The driver default verbose level is 1. This command allows to change 
	    th driver verbose level after boot-up.
	
	8.9 Reset all logical units of a target
	
	    resetdev <target>
	
	    target:    target number
	    The driver will try to send a BUS DEVICE RESET message to the target.
	    (Only supported by the SYM53C8XX driver and provided for test purpose)
	
	8.10 Abort all tasks of all logical units of a target
	
	    cleardev <target>
	
	    target:    target number
	    The driver will try to send a ABORT message to all the logical units 
	    of the target.
	    (Only supported by the SYM53C8XX driver and provided for test purpose)
	
	
	9. Configuration parameters
	
	If the firmware of all your devices is perfect enough, all the
	features supported by the driver can be enabled at start-up.  However,
	if only one has a flaw for some SCSI feature, you can disable the
	support by the driver of this feature at linux start-up and enable
	this feature after boot-up only for devices that support it safely.
	
	CONFIG_SCSI_NCR53C8XX_IOMAPPED       (default answer: n)
	    Answer "y" if you suspect your mother board to not allow memory mapped I/O.
	    May slow down performance a little.  This option is required by
	    Linux/PPC and is used no matter what you select here.  Linux/PPC
	    suffers no performance loss with this option since all IO is memory
	    mapped anyway.
	
	CONFIG_SCSI_NCR53C8XX_DEFAULT_TAGS    (default answer: 8)
	    Default tagged command queue depth.
	
	CONFIG_SCSI_NCR53C8XX_MAX_TAGS         (default answer: 8)
	    This option allows you to specify the maximum number of tagged commands 
	    that can be queued to a device. The maximum supported value is 32.
	
	CONFIG_SCSI_NCR53C8XX_SYNC            (default answer: 5)
	    This option allows you to specify the frequency in MHz the driver 
	    will use at boot time for synchronous data transfer negotiations.
	    This frequency can be changed later with the "setsync" control command.
	    0 means "asynchronous data transfers".
	
	CONFIG_SCSI_NCR53C8XX_FORCE_SYNC_NEGO (default answer: n)
	    Force synchronous negotiation for all SCSI-2 devices.
	    Some SCSI-2 devices do not report this feature in byte 7 of inquiry 
	    response but do support it properly (TAMARACK scanners for example).
	
	CONFIG_SCSI_NCR53C8XX_NO_DISCONNECT   (default and only reasonable answer: n)
	    If you suspect a device of yours does not properly support disconnections,
	    you can answer "y". Then, all SCSI devices will never disconnect the bus 
	    even while performing long SCSI operations.
	
	CONFIG_SCSI_NCR53C8XX_SYMBIOS_COMPAT
	    Genuine SYMBIOS boards use GPIO0 in output for controller LED and GPIO3 
	    bit as a flag indicating singled-ended/differential interface.
	    If all the boards of your system are genuine SYMBIOS boards or use
	    BIOS and drivers from SYMBIOS, you would want to enable this option.
	    This option must NOT be enabled if your system has at least one 53C8XX 
	    based scsi board with a vendor-specific BIOS.
	    For example, Tekram DC-390/U, DC-390/W and DC-390/F scsi controllers 
	    use a vendor-specific BIOS and are known to not use SYMBIOS compatible 
	    GPIO wiring. So, this option must not be enabled if your system has 
	    such a board installed.
	
	CONFIG_SCSI_NCR53C8XX_NVRAM_DETECT
	    Enable support for reading the serial NVRAM data on Symbios and
	    some Symbios compatible cards, and Tekram DC390W/U/F cards. Useful for
	    systems with more than one Symbios compatible controller where at least
	    one has a serial NVRAM, or for a system with a mixture of Symbios and
	    Tekram cards. Enables setting the boot order of host adaptors
	    to something other than the default order or "reverse probe" order. 
	    Also enables Symbios and Tekram cards to be distinguished so
	    CONFIG_SCSI_NCR53C8XX_SYMBIOS_COMPAT may be set in a system with a
	    mixture of Symbios and Tekram cards so the Symbios cards can make use of
	    the full range of Symbios features, differential, led pin, without
	    causing problems for the Tekram card(s).
	
	10. Boot setup commands
	
	10.1 Syntax
	
	Setup commands can be passed to the driver either at boot time or as a 
	string variable using 'insmod'.
	
	A boot setup command for the ncr53c8xx (sym53c8xx) driver begins with the 
	driver name "ncr53c8xx="(sym53c8xx). The kernel syntax parser then expects 
	an optional list of integers separated with comma followed by an optional 
	list of comma-separated strings. Example of boot setup command under lilo 
	prompt:
	
	lilo: linux root=/dev/hda2 ncr53c8xx=tags:4,sync:10,debug:0x200
	
	- enable tagged commands, up to 4 tagged commands queued.
	- set synchronous negotiation speed to 10 Mega-transfers / second.
	- set DEBUG_NEGO flag.
	
	Since comma seems not to be allowed when defining a string variable using  
	'insmod', the driver also accepts <space> as option separator. 
	The following command will install driver module with the same options as 
	above.
	
	    insmod ncr53c8xx.o ncr53c8xx="tags:4 sync:10 debug:0x200"
	
	For the moment, the integer list of arguments is discarded by the driver. 
	It will be used in the future in order to allow a per controller setup.
	
	Each string argument must be specified as "keyword:value". Only lower-case 
	characters and digits are allowed.
	
	In a system that contains multiple 53C8xx adapters insmod will install the 
	specified driver on each adapter. To exclude a chip use the 'excl' keyword.
	
	The sequence of commands, 
	
	    insmod sym53c8xx sym53c8xx=excl:0x1400
	    insmod ncr53c8xx
	
	installs the sym53c8xx driver on all adapters except the one at IO port 
	address 0x1400 and then installs the ncr53c8xx driver to the adapter at IO 
	port address 0x1400.
	
	
	10.2 Available arguments
	
	10.2.1  Master parity checking
	        mpar:y     enabled
	        mpar:n     disabled
	
	10.2.2  Scsi parity checking
	        spar:y     enabled
	        spar:n     disabled
	
	10.2.3  Scsi disconnections
	        disc:y     enabled
	        disc:n     disabled
	 
	10.2.4  Special features
	   Only apply to 810A, 825A, 860, 875 and 895 controllers.
	   Have no effect with other ones.
	        specf:y    (or 1) enabled
	        specf:n    (or 0) disabled
	        specf:3           enabled except Memory Write And Invalidate
	   The default driver setup is 'specf:3'. As a consequence, option 'specf:y' 
	   must be specified in the boot setup command to enable Memory Write And 
	   Invalidate.
	
	10.2.5  Ultra SCSI support
	   Only apply to 860, 875, 895, 895a, 896, 1010 and 1010_66 controllers.
	   Have no effect with other ones.
	        ultra:n    All ultra speeds enabled
	        ultra:2    Ultra2 enabled
	        ultra:1    Ultra enabled
	        ultra:0    Ultra speeds disabled
	
	10.2.6  Default number of tagged commands
	        tags:0     (or tags:1 ) tagged command queuing disabled
	        tags:#tags (#tags  > 1) tagged command queuing enabled
	  #tags will be truncated to the max queued commands configuration parameter.
	  This option also allows to specify a command queue depth for each device 
	  that support tagged command queueing.
	  Example:
	      ncr53c8xx=tags:10/t2t3q16-t5q24/t1u2q32
	               will set devices queue depth as follow:
	      - controller #0 target #2 and target #3                  -> 16 commands,
	      - controller #0 target #5                                -> 24 commands,
	      - controller #1 target #1 logical unit #2                -> 32 commands,
	      - all other logical units (all targets, all controllers) -> 10 commands.
	
	10.2.7  Default synchronous period factor
	        sync:255     disabled (asynchronous transfer mode)
	        sync:#factor
	  #factor = 10     Ultra-2 SCSI 40 Mega-transfers / second
	  #factor = 11     Ultra-2 SCSI 33 Mega-transfers / second
	  #factor < 25     Ultra   SCSI 20 Mega-transfers / second
	  #factor < 50     Fast    SCSI-2
	
	  In all cases, the driver will use the minimum transfer period supported by 
	  controllers according to NCR53C8XX chip type.
	
	10.2.8  Negotiate synchronous with all devices
	        (force sync nego)
	        fsn:y      enabled
	        fsn:n      disabled
	
	10.2.9  Verbosity level
	        verb:0     minimal
	        verb:1     normal
	        verb:2     too much
	
	10.2.10 Debug mode
	        debug:0	 clear debug flags
	        debug:#x   set debug flags
	  #x is an integer value combining the following power-of-2 values:
	  DEBUG_ALLOC       0x1
	  DEBUG_PHASE       0x2
	  DEBUG_POLL        0x4
	  DEBUG_QUEUE       0x8
	  DEBUG_RESULT     0x10
	  DEBUG_SCATTER    0x20
	  DEBUG_SCRIPT     0x40
	  DEBUG_TINY       0x80
	  DEBUG_TIMING    0x100
	  DEBUG_NEGO      0x200
	  DEBUG_TAGS      0x400
	  DEBUG_FREEZE    0x800
	  DEBUG_RESTART  0x1000
	
	  You can play safely with DEBUG_NEGO. However, some of these flags may 
	  generate bunches of syslog messages. 
	
	10.2.11 Burst max
	        burst:0    burst disabled
	        burst:255  get burst length from initial IO register settings.
	        burst:#x   burst enabled (1<<#x burst transfers max)
	  #x is an integer value which is log base 2 of the burst transfers max.
	  The NCR53C875 and NCR53C825A support up to 128 burst transfers (#x = 7).
	  Other chips only support up to 16 (#x = 4).
	  This is a maximum value. The driver set the burst length according to chip 
	  and revision ids. By default the driver uses the maximum value supported 
	  by the chip.
	
	10.2.12 LED support
	        led:1      enable  LED support
	        led:0      disable LED support
	  Donnot enable LED support if your scsi board does not use SDMS BIOS.
	  (See 'Configuration parameters')
	
	10.2.13 Max wide
	        wide:1      wide scsi enabled
	        wide:0      wide scsi disabled
	  Some scsi boards use a 875 (ultra wide) and only supply narrow connectors.
	  If you have connected a wide device with a 50 pins to 68 pins cable 
	  converter, any accepted wide negotiation will break further data transfers.
	  In such a case, using "wide:0" in the bootup command will be helpful. 
	
	10.2.14 Differential mode
	        diff:0	never set up diff mode
	        diff:1	set up diff mode if BIOS set it
	        diff:2	always set up diff mode
	        diff:3	set diff mode if GPIO3 is not set
	
	10.2.15 IRQ mode
	        irqm:0     always open drain
	        irqm:1     same as initial settings (assumed BIOS settings)
	        irqm:2     always totem pole
	        irqm:0x10  driver will not use IRQF_SHARED flag when requesting irq
	        irqm:0x20  driver will not use IRQF_DISABLED flag when requesting irq
	
	    (Bits 0x10 and 0x20 can be combined with hardware irq mode option)
	
	10.2.16 Reverse probe
	        revprob:n   probe chip ids from the PCI configuration in this order:
	                    810, 815, 820, 860, 875, 885, 895, 896
	        revprob:y   probe chip ids in the reverse order.
	
	10.2.17 Fix up PCI configuration space
	        pcifix:<option bits>
	
	    Available option bits:
	        0x0:   No attempt to fix PCI configuration space registers values.
	        0x1:   Set PCI cache-line size register if not set.
	        0x2:   Set write and invalidate bit in PCI command register.
	        0x4:   Increase if necessary PCI latency timer according to burst max.
	
	    Use 'pcifix:7' in order to allow the driver to fix up all PCI features.
	
	10.2.18 Serial NVRAM
	        nvram:n     do not look for serial NVRAM
	        nvram:y     test controllers for onboard serial NVRAM
	        (alternate binary form)
	        mvram=<bits options>
	        0x01   look for NVRAM  (equivalent to nvram=y)
	        0x02   ignore NVRAM "Synchronous negotiation" parameters for all devices
	        0x04   ignore NVRAM "Wide negotiation"  parameter for all devices
	        0x08   ignore NVRAM "Scan at boot time" parameter for all devices
	        0x80   also attach controllers set to OFF in the NVRAM (sym53c8xx only)
	
	10.2.19 Check SCSI BUS 
	        buschk:<option bits>
	
	    Available option bits:
	        0x0:   No check.
	        0x1:   Check and do not attach the controller on error.  
	        0x2:   Check and just warn on error.
	        0x4:   Disable SCSI bus integrity checking.
	
	10.2.20 Exclude a host from being attached
	        excl=<io_address>
	
	    Prevent host at a given io address from being attached.
	    For example 'ncr53c8xx=excl:0xb400,excl:0xc000' indicate to the 
	    ncr53c8xx driver not to attach hosts at address 0xb400 and 0xc000.
	
	10.2.21 Suggest a default SCSI id for hosts
	        hostid:255	no id suggested.
	        hostid:#x   (0 < x < 7) x suggested for hosts SCSI id.
	
	    If a host SCSI id is available from the NVRAM, the driver will ignore 
	    any value suggested as boot option. Otherwise, if a suggested value 
	    different from 255 has been supplied, it will use it. Otherwise, it will 
	    try to deduce the value previously set in the hardware and use value 
	    7 if the hardware value is zero.
	
	10.2.22 Enable use of IMMEDIATE ARBITRATION
	        (only supported by the sym53c8xx driver. See 10.7 for more details)
	        iarb:0    do not use this feature.
	        iarb:#x   use this feature according to bit fields as follow:
	
	    bit 0 (1) : enable IARB each time the initiator has been reselected 
	                when it arbitrated for the SCSI BUS.
	    (#x >> 4) : maximum number of successive settings of IARB if the initiator 
	                win arbitration and it has other commands to send to a device.
	
	Boot fail safe
	    safe:y	load the following assumed fail safe initial setup
	
	  master parity			disabled		mpar:n
	  scsi parity			enabled			spar:y
	  disconnections		not allowed		disc:n
	  special features		disabled		specf:n
	  ultra scsi			disabled		ultra:n
	  force sync negotiation	disabled		fsn:n
	  reverse probe			disabled		revprob:n
	  PCI fix up                    disabled                pcifix:0
	  serial NVRAM                  enabled                 nvram:y
	  verbosity level		2			verb:2
	  tagged command queuing	disabled		tags:0
	  synchronous negotiation	disabled		sync:255
	  debug flags			none			debug:0
	  burst length			from BIOS settings	burst:255
	  LED support			disabled		led:0
	  wide support			disabled		wide:0
	  settle time			10 seconds		settle:10
	  differential support		from BIOS settings	diff:1
	  irq mode			from BIOS settings	irqm:1
	  SCSI BUS check		do not attach on error	buschk:1
	  immediate arbitration		disabled		iarb:0
	
	10.3 Advised boot setup commands
	
	If the driver has been configured with default options, the equivalent 
	boot setup is:
	
	   ncr53c8xx=mpar:y,spar:y,disc:y,specf:3,fsn:n,ultra:2,fsn:n,revprob:n,verb:1\
	             tags:0,sync:50,debug:0,burst:7,led:0,wide:1,settle:2,diff:0,irqm:0
	
	For an installation diskette or a safe but not fast system,
	boot setup can be:
	
	    ncr53c8xx=safe:y,mpar:y,disc:y
	    ncr53c8xx=safe:y,disc:y
	    ncr53c8xx=safe:y,mpar:y
	    ncr53c8xx=safe:y
	
	My personal system works flawlessly with the following equivalent setup:
	
	   ncr53c8xx=mpar:y,spar:y,disc:y,specf:1,fsn:n,ultra:2,fsn:n,revprob:n,verb:1\
	             tags:32,sync:12,debug:0,burst:7,led:1,wide:1,settle:2,diff:0,irqm:0
	
	The driver prints its actual setup when verbosity level is 2. You can try 
	"ncr53c8xx=verb:2" to get the "static" setup of the driver, or add "verb:2" 
	to your boot setup command in order to check the actual setup the driver is 
	using.
	
	10.4 PCI configuration fix-up boot option
	
	pcifix:<option bits>
	
	Available option bits:
	    0x1:     Set PCI cache-line size register if not set.
	    0x2:     Set write and invalidate bit in PCI command register.
	
	Use 'pcifix:3' in order to allow the driver to fix both PCI features.
	
	These options only apply to new SYMBIOS chips 810A, 825A, 860, 875 
	and 895 and are only supported for Pentium and 486 class processors.
	Recent SYMBIOS 53C8XX scsi processors are able to use PCI read multiple 
	and PCI write and invalidate commands. These features require the 
	cache line size register to be properly set in the PCI configuration 
	space of the chips. On the other hand, chips will use PCI write and 
	invalidate commands only if the corresponding bit is set to 1 in the 
	PCI command register.
	
	Not all PCI bioses set the PCI cache line register and the PCI write and 
	invalidate bit in the PCI configuration space of 53C8XX chips.
	Optimized PCI accesses may be broken for some PCI/memory controllers or 
	make problems with some PCI boards.
	
	This fix-up worked flawlessly on my previous system.
	(MB Triton HX / 53C875 / 53C810A)
	I use these options at my own risks as you will do if you decide to 
	use them too.
	
	
	10.5 Serial NVRAM support boot option
	
	nvram:n     do not look for serial NVRAM
	nvram:y     test controllers for onboard serial NVRAM
	
	This option can also been entered as an hexadecimal value that allows 
	to control what information the driver will get from the NVRAM and what 
	information it will ignore.
	For details see '17. Serial NVRAM support'.
	
	When this option is enabled, the driver tries to detect all boards using 
	a Serial NVRAM. This memory is used to hold user set up parameters.
	
	The parameters the driver is able to get from the NVRAM depend on the 
	data format used, as follow:
	
	                                 Tekram format      Symbios format
	General and host parameters
	    Boot order                         N                   Y
	    Host SCSI ID                       Y                   Y
	    SCSI parity checking               Y                   Y
	    Verbose boot messages              N                   Y
	SCSI devices parameters
	    Synchronous transfer speed         Y                   Y
	    Wide 16 / Narrow                   Y                   Y
	    Tagged Command Queuing enabled     Y                   Y
	    Disconnections enabled             Y                   Y
	    Scan at boot time                  N                   Y
	
	In order to speed up the system boot, for each device configured without 
	the "scan at boot time" option, the driver forces an error on the 
	first TEST UNIT READY command received for this device.
	
	Some SDMS BIOS revisions seem to be unable to boot cleanly with very fast 
	hard disks. In such a situation you cannot configure the NVRAM with 
	optimized parameters value.
	
	The 'nvram' boot option can be entered in hexadecimal form in order 
	to ignore some options configured in the NVRAM, as follow:
	
	mvram=<bits options>
	      0x01   look for NVRAM  (equivalent to nvram=y)
	      0x02   ignore NVRAM "Synchronous negotiation" parameters for all devices
	      0x04   ignore NVRAM "Wide negotiation"  parameter for all devices
	      0x08   ignore NVRAM "Scan at boot time" parameter for all devices
	      0x80   also attach controllers set to OFF in the NVRAM (sym53c8xx only)
	
	Option 0x80 is only supported by the sym53c8xx driver and is disabled by 
	default. Result is that, by default (option not set), the sym53c8xx driver 
	will not attach controllers set to OFF in the NVRAM.
	
	The ncr53c8xx always tries to attach all the controllers. Option 0x80 has 
	not been added to the ncr53c8xx driver, since it has been reported to 
	confuse users who use this driver since a long time. If you desire a 
	controller not to be attached by the ncr53c8xx driver at Linux boot, you 
	must use the 'excl' driver boot option.
	
	10.6 SCSI BUS checking boot option.
	
	When this option is set to a non-zero value, the driver checks SCSI lines 
	logic state, 100 micro-seconds after having asserted the SCSI RESET line.
	The driver just reads SCSI lines and checks all lines read FALSE except RESET.
	Since SCSI devices shall release the BUS at most 800 nano-seconds after SCSI 
	RESET has been asserted, any signal to TRUE may indicate a SCSI BUS problem.
	Unfortunately, the following common SCSI BUS problems are not detected:
	- Only 1 terminator installed.
	- Misplaced terminators.
	- Bad quality terminators.
	On the other hand, either bad cabling, broken devices, not conformant 
	devices, ... may cause a SCSI signal to be wrong when te driver reads it.
	
	10.7 IMMEDIATE ARBITRATION boot option
	
	This option is only supported by the SYM53C8XX driver (not by the NCR53C8XX).
	
	SYMBIOS 53C8XX chips are able to arbitrate for the SCSI BUS as soon as they 
	have detected an expected disconnection (BUS FREE PHASE). For this process 
	to be started, bit 1 of SCNTL1 IO register must be set when the chip is 
	connected to the SCSI BUS.
	
	When this feature has been enabled for the current connection, the chip has 
	every chance to win arbitration if only devices with lower priority are 
	competing for the SCSI BUS. By the way, when the chip is using SCSI id 7, 
	then it will for sure win the next SCSI BUS arbitration.
	
	Since, there is no way to know what devices are trying to arbitrate for the 
	BUS, using this feature can be extremely unfair. So, you are not advised
	to enable it, or at most enable this feature for the case the chip lost 
	the previous arbitration (boot option 'iarb:1').
	
	This feature has the following advantages:
	
	a) Allow the initiator with ID 7 to win arbitration when it wants so.
	b) Overlap at least 4 micro-seconds of arbitration time with the execution 
	   of SCRIPTS that deal with the end of the current connection and that 
	   starts the next job.
	
	Hmmm... But (a) may just prevent other devices from reselecting the initiator, 
	and delay data transfers or status/completions, and (b) may just waste 
	SCSI BUS bandwidth if the SCRIPTS execution lasts more than 4 micro-seconds.
	
	The use of IARB needs the SCSI_NCR_IARB_SUPPORT option to have been defined 
	at compile time and the 'iarb' boot option to have been set to a non zero 
	value at boot time. It is not that useful for real work, but can be used 
	to stress SCSI devices or for some applications that can gain advantage of 
	it. By the way, if you experience badnesses like 'unexpected disconnections', 
	'bad reselections', etc... when using IARB on heavy IO load, you should not 
	be surprised, because force-feeding anything and blocking its arse at the 
	same time cannot work for a long time. :-))
	
	
	11. Some constants and flags of the ncr53c8xx.h header file
	
	Some of these are defined from the configuration parameters.  To
	change other "defines", you must edit the header file.  Do that only
	if you know what you are doing.
	
	SCSI_NCR_SETUP_SPECIAL_FEATURES	(default: defined)
		If defined, the driver will enable some special features according  
		to chip and revision id.
	        For 810A, 860, 825A, 875 and 895 scsi chips, this option enables 
		support of features that reduce load of PCI bus and memory accesses 
		during  scsi transfer processing: burst op-code fetch, read multiple, 
	        read line, prefetch, cache line, write and invalidate, 
	        burst 128 (875 only), large dma fifo (875 only), offset 16 (875 only).
		Can be changed by the following boot setup command:
			ncr53c8xx=specf:n
	
	SCSI_NCR_IOMAPPED		(default: not defined)
		If defined, normal I/O is forced.
	
	SCSI_NCR_SHARE_IRQ		(default: defined)
		If defined, request shared IRQ.
		
	SCSI_NCR_MAX_TAGS		(default: 8)
		Maximum number of simultaneous tagged commands to a device.
		Can be changed by "settags <target> <maxtags>"
	
	SCSI_NCR_SETUP_DEFAULT_SYNC     (default: 50)
		Transfer period factor the driver will use at boot time for synchronous 
		negotiation. 0 means asynchronous.
		Can be changed by "setsync <target> <period factor>"
	
	SCSI_NCR_SETUP_DEFAULT_TAGS     (default: 8)
		Default number of simultaneous tagged commands to a device.
		< 1 means tagged command queuing disabled at start-up.
	
	SCSI_NCR_ALWAYS_SIMPLE_TAG	(default: defined)
		Use SIMPLE TAG for read and write commands.
		Can be changed by "setorder <ordered|simple|default>"
	
	SCSI_NCR_SETUP_DISCONNECTION	(default: defined)
		If defined, targets are allowed to disconnect.
	
	SCSI_NCR_SETUP_FORCE_SYNC_NEGO	(default: not defined)
		If defined, synchronous negotiation is tried for all SCSI-2 devices.
		Can be changed by "setsync <target> <period>"
	
	SCSI_NCR_SETUP_MASTER_PARITY	(default: defined)
		If defined, master parity checking is enabled.
	
	SCSI_NCR_SETUP_MASTER_PARITY	(default: defined)
		If defined, SCSI parity checking is enabled.
	
	SCSI_NCR_PROFILE_SUPPORT	(default: not defined)
		If defined, profiling information is gathered.
	
	SCSI_NCR_MAX_SCATTER		(default: 128)
		Scatter list size of the driver ccb.
	
	SCSI_NCR_MAX_TARGET		(default: 16)
		Max number of targets per host.
	
	SCSI_NCR_MAX_HOST		(default: 2)
		Max number of host controllers.
	
	SCSI_NCR_SETTLE_TIME		(default: 2)
		Number of seconds the driver will wait after reset.
	
	SCSI_NCR_TIMEOUT_ALERT		(default: 3)
		If a pending command will time out after this amount of seconds,
		an ordered tag is used for the next command.
		Avoids timeouts for unordered tagged commands.
	
	SCSI_NCR_CAN_QUEUE		(default: 7*SCSI_NCR_MAX_TAGS)
		Max number of commands that can be queued to a host.
	
	SCSI_NCR_CMD_PER_LUN		(default: SCSI_NCR_MAX_TAGS)
		Max number of commands queued to a host for a device.
	
	SCSI_NCR_SG_TABLESIZE		(default: SCSI_NCR_MAX_SCATTER-1)
		Max size of the Linux scatter/gather list.
	
	SCSI_NCR_MAX_LUN	(default: 8)
		Max number of LUNs per target.
	
	
	12. Installation
	
	This driver is part of the linux kernel distribution.
	Driver files are located in the sub-directory "drivers/scsi" of the 
	kernel source tree.
	
	Driver files:
	
		README.ncr53c8xx	: this file
		ChangeLog.ncr53c8xx	: change log
		ncr53c8xx.h		: definitions
		ncr53c8xx.c		: the driver code
	
	New driver versions are made available separately in order to allow testing 
	changes and new features prior to including them into the linux kernel 
	distribution. The following URL provides information on latest available 
	patches: 
	
	      ftp://ftp.tux.org/pub/people/gerard-roudier/README
	
	
	13. Architecture dependent features.
	
	<Not yet written>
	
	
	14. Known problems
	
	14.1 Tagged commands with Iomega Jaz device
	
	I have not tried this device, however it has been reported to me the
	following: This device is capable of Tagged command queuing. However
	while spinning up, it rejects Tagged commands. This behaviour is
	conforms to 6.8.2 of SCSI-2 specifications. The current behaviour of
	the driver in that situation is not satisfying. So do not enable
	Tagged command queuing for devices that are able to spin down.  The
	other problem that may appear is timeouts. The only way to avoid
	timeouts seems to edit linux/drivers/scsi/sd.c and to increase the
	current timeout values.
	
	14.2 Device names change when another controller is added.
	
	When you add a new NCR53C8XX chip based controller to a system that already 
	has one or more controllers of this family, it may happen that the order 
	the driver registers them to the kernel causes problems due to device 
	name changes.
	When at least one controller uses NvRAM, SDMS BIOS version 4 allows you to 
	define the order the BIOS will scan the scsi boards. The driver attaches 
	controllers according to BIOS information if NvRAM detect option is set.
	
	If your controllers do not have NvRAM, you can:
	
	- Ask the driver to probe chip ids in reverse order from the boot command
	  line: ncr53c8xx=revprob:y
	- Make appropriate changes in the fstab.
	- Use the 'scsidev' tool from Eric Youngdale.
	
	14.3 Using only 8 bit devices with a WIDE SCSI controller.
	
	When only 8 bit NARROW devices are connected to a 16 bit WIDE SCSI controller, 
	you must ensure that lines of the wide part of the SCSI BUS are pulled-up.
	This can be achieved by ENABLING the WIDE TERMINATOR portion of the SCSI 
	controller card.
	The TYAN 1365 documentation revision 1.2 is not correct about such settings.
	(page 10, figure 3.3).
	
	14.4 Possible data corruption during a Memory Write and Invalidate
	
	This problem is described in SYMBIOS DEL 397, Part Number 69-039241, ITEM 4.
	
	In some complex situations, 53C875 chips revision <= 3 may start a PCI 
	Write and Invalidate Command at a not cache-line-aligned 4 DWORDS boundary.
	This is only possible when Cache Line Size is 8 DWORDS or greater.
	Pentium systems use a 8 DWORDS cache line size and so are concerned by 
	this chip bug, unlike i486 systems that use a 4 DWORDS cache line size.
	
	When this situation occurs, the chip may complete the Write and Invalidate 
	command after having only filled part of the last cache line involved in 
	the transfer, leaving to data corruption the remainder of this cache line.
	
	Not using Write And Invalidate obviously gets rid of this chip bug, and so 
	it is now the default setting of the driver.
	However, for people like me who want to enable this feature, I have added 
	part of a work-around suggested by SYMBIOS. This work-around resets the 
	addressing logic when the DATA IN phase is entered and so prevents the bug 
	from being triggered for the first SCSI MOVE of the phase. This work-around 
	should be enough according to the following:
	
	The only driver internal data structure that is greater than 8 DWORDS  and 
	that is moved by the SCRIPTS processor is the 'CCB header' that contains 
	the context of the SCSI transfer. This data structure is aligned on 8 DWORDS 
	boundary (Pentium Cache Line Size), and so is immune to this chip bug, at 
	least on Pentium systems.
	But the conditions of this bug can be met when a SCSI read command is 
	performed using a buffer that is 4 DWORDS but not cache-line aligned.
	This cannot happen under Linux when scatter/gather lists are used since 
	they only refer to system buffers that are well aligned. So, a work around 
	may only be needed under Linux when a scatter/gather list is not used and 
	when the SCSI DATA IN phase is reentered after a phase mismatch.
	
	14.5 IRQ sharing problems
	
	When an IRQ is shared by devices that are handled by different drivers, it 
	may happen that one driver complains about the request of the IRQ having 
	failed. Inder Linux-2.0, this may be due to one driver having requested the 
	IRQ using the IRQF_DISABLED flag but some other having requested the same IRQ
	without this flag. Under both Linux-2.0 and linux-2.2, this may be caused by 
	one driver not having requested the IRQ with the IRQF_SHARED flag.
	
	By default, the ncr53c8xx and sym53c8xx drivers request IRQs with both the 
	IRQF_DISABLED and the IRQF_SHARED flag under Linux-2.0 and with only the IRQF_SHARED
	flag under Linux-2.2.
	
	Under Linux-2.0, you can disable use of IRQF_DISABLED flag from the boot
	command line by using the following option:
	
	     ncr53c8xx=irqm:0x20   (for the generic ncr53c8xx driver)
	     sym53c8xx=irqm:0x20   (for the sym53c8xx driver)
	
	If this does not fix the problem, then you may want to check how all other 
	drivers are requesting the IRQ and report the problem. Note that if at least 
	a single driver does not request the IRQ with the IRQF_SHARED flag (share IRQ),
	then the request of the IRQ obviously will not succeed for all the drivers.
	
	15. SCSI problem troubleshooting
	
	15.1 Problem tracking
	
	Most SCSI problems are due to a non conformant SCSI bus or to buggy
	devices.  If unfortunately you have SCSI problems, you can check the
	following things:
	
	- SCSI bus cables
	- terminations at both end of the SCSI chain
	- linux syslog messages (some of them may help you)
	
	If you do not find the source of problems, you can configure the
	driver with no features enabled.
	
	- only asynchronous data transfers
	- tagged commands disabled
	- disconnections not allowed
	
	Now, if your SCSI bus is ok, your system have every chance to work
	with this safe configuration but performances will not be optimal.
	
	If it still fails, then you can send your problem description to
	appropriate mailing lists or news-groups.  Send me a copy in order to
	be sure I will receive it.  Obviously, a bug in the driver code is
	possible.
	
	     My email address: Gerard Roudier <groudier[AT]free[DOT]fr>
	
	Allowing disconnections is important if you use several devices on
	your SCSI bus but often causes problems with buggy devices.
	Synchronous data transfers increases throughput of fast devices like
	hard disks.  Good SCSI hard disks with a large cache gain advantage of
	tagged commands queuing.
	
	Try to enable one feature at a time with control commands.  For example:
	
	- echo "setsync all 25" >/proc/scsi/ncr53c8xx/0
	  Will enable fast synchronous data transfer negotiation for all targets.
	
	- echo "setflag 3" >/proc/scsi/ncr53c8xx/0
	  Will reset flags (no_disc) for target 3, and so will allow it to disconnect 
	  the SCSI Bus.
	
	- echo "settags 3 8" >/proc/scsi/ncr53c8xx/0
	  Will enable tagged command queuing for target 3 if that device supports it.
	
	Once you have found the device and the feature that cause problems, just