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Based on kernel version 3.16. Page generated on 2014-08-06 21:40 EST.

1	Linux for S/390 and zSeries
2	
3	Common Device Support (CDS)
4	Device Driver I/O Support Routines
5	
6	Authors : Ingo Adlung
7		  Cornelia Huck
8	
9	Copyright, IBM Corp. 1999-2002
10	
11	Introduction
12	
13	This document describes the common device support routines for Linux/390.
14	Different than other hardware architectures, ESA/390 has defined a unified
15	I/O access method. This gives relief to the device drivers as they don't
16	have to deal with different bus types, polling versus interrupt
17	processing, shared versus non-shared interrupt processing, DMA versus port
18	I/O (PIO), and other hardware features more. However, this implies that
19	either every single device driver needs to implement the hardware I/O
20	attachment functionality itself, or the operating system provides for a
21	unified method to access the hardware, providing all the functionality that
22	every single device driver would have to provide itself.
23	
24	The document does not intend to explain the ESA/390 hardware architecture in
25	every detail.This information can be obtained from the ESA/390 Principles of
26	Operation manual (IBM Form. No. SA22-7201).
27	
28	In order to build common device support for ESA/390 I/O interfaces, a
29	functional layer was introduced that provides generic I/O access methods to
30	the hardware. 
31	
32	The common device support layer comprises the I/O support routines defined 
33	below. Some of them implement common Linux device driver interfaces, while 
34	some of them are ESA/390 platform specific.
35	
36	Note:
37	In order to write a driver for S/390, you also need to look into the interface
38	described in Documentation/s390/driver-model.txt.
39	
40	Note for porting drivers from 2.4:
41	The major changes are:
42	* The functions use a ccw_device instead of an irq (subchannel).
43	* All drivers must define a ccw_driver (see driver-model.txt) and the associated
44	  functions.
45	* request_irq() and free_irq() are no longer done by the driver.
46	* The oper_handler is (kindof) replaced by the probe() and set_online() functions
47	  of the ccw_driver.
48	* The not_oper_handler is (kindof) replaced by the remove() and set_offline()
49	  functions of the ccw_driver.
50	* The channel device layer is gone.
51	* The interrupt handlers must be adapted to use a ccw_device as argument.
52	  Moreover, they don't return a devstat, but an irb.
53	* Before initiating an io, the options must be set via ccw_device_set_options().
54	* Instead of calling read_dev_chars()/read_conf_data(), the driver issues
55	  the channel program and handles the interrupt itself.
56	
57	ccw_device_get_ciw()
58	   get commands from extended sense data.
59	
60	ccw_device_start()	
61	ccw_device_start_timeout()
62	ccw_device_start_key()
63	ccw_device_start_key_timeout()
64	   initiate an I/O request.
65	
66	ccw_device_resume()
67	   resume channel program execution.
68	
69	ccw_device_halt()	
70	   terminate the current I/O request processed on the device.
71	
72	do_IRQ()	
73	   generic interrupt routine. This function is called by the interrupt entry
74	   routine whenever an I/O interrupt is presented to the system. The do_IRQ()
75	   routine determines the interrupt status and calls the device specific
76	   interrupt handler according to the rules (flags) defined during I/O request
77	   initiation with do_IO().
78	
79	The next chapters describe the functions other than do_IRQ() in more details.
80	The do_IRQ() interface is not described, as it is called from the Linux/390
81	first level interrupt handler only and does not comprise a device driver
82	callable interface. Instead, the functional description of do_IO() also
83	describes the input to the device specific interrupt handler.
84	
85	Note: All explanations apply also to the 64 bit architecture s390x.
86	
87	
88	Common Device Support (CDS) for Linux/390 Device Drivers
89	
90	General Information
91	
92	The following chapters describe the I/O related interface routines the
93	Linux/390 common device support (CDS) provides to allow for device specific
94	driver implementations on the IBM ESA/390 hardware platform. Those interfaces
95	intend to provide the functionality required by every device driver
96	implementation to allow to drive a specific hardware device on the ESA/390
97	platform. Some of the interface routines are specific to Linux/390 and some
98	of them can be found on other Linux platforms implementations too.
99	Miscellaneous function prototypes, data declarations, and macro definitions
100	can be found in the architecture specific C header file
101	linux/arch/s390/include/asm/irq.h.
102	
103	Overview of CDS interface concepts
104	
105	Different to other hardware platforms, the ESA/390 architecture doesn't define
106	interrupt lines managed by a specific interrupt controller and bus systems
107	that may or may not allow for shared interrupts, DMA processing, etc.. Instead,
108	the ESA/390 architecture has implemented a so called channel subsystem, that
109	provides a unified view of the devices physically attached to the systems.
110	Though the ESA/390 hardware platform knows about a huge variety of different
111	peripheral attachments like disk devices (aka. DASDs), tapes, communication
112	controllers, etc. they can all be accessed by a well defined access method and
113	they are presenting I/O completion a unified way : I/O interruptions. Every
114	single device is uniquely identified to the system by a so called subchannel,
115	where the ESA/390 architecture allows for 64k devices be attached.
116	
117	Linux, however, was first built on the Intel PC architecture, with its two
118	cascaded 8259 programmable interrupt controllers (PICs), that allow for a
119	maximum of 15 different interrupt lines. All devices attached to such a system
120	share those 15 interrupt levels. Devices attached to the ISA bus system must
121	not share interrupt levels (aka. IRQs), as the ISA bus bases on edge triggered
122	interrupts. MCA, EISA, PCI and other bus systems base on level triggered
123	interrupts, and therewith allow for shared IRQs. However, if multiple devices
124	present their hardware status by the same (shared) IRQ, the operating system
125	has to call every single device driver registered on this IRQ in order to
126	determine the device driver owning the device that raised the interrupt.
127	
128	Up to kernel 2.4, Linux/390 used to provide interfaces via the IRQ (subchannel).
129	For internal use of the common I/O layer, these are still there. However, 
130	device drivers should use the new calling interface via the ccw_device only.
131	
132	During its startup the Linux/390 system checks for peripheral devices. Each
133	of those devices is uniquely defined by a so called subchannel by the ESA/390
134	channel subsystem. While the subchannel numbers are system generated, each
135	subchannel also takes a user defined attribute, the so called device number.
136	Both subchannel number and device number cannot exceed 65535. During sysfs
137	initialisation, the information about control unit type and device types that 
138	imply specific I/O commands (channel command words - CCWs) in order to operate
139	the device are gathered. Device drivers can retrieve this set of hardware
140	information during their initialization step to recognize the devices they
141	support using the information saved in the struct ccw_device given to them.
142	This methods implies that Linux/390 doesn't require to probe for free (not
143	armed) interrupt request lines (IRQs) to drive its devices with. Where
144	applicable, the device drivers can use issue the READ DEVICE CHARACTERISTICS
145	ccw to retrieve device characteristics in its online routine.
146	
147	In order to allow for easy I/O initiation the CDS layer provides a
148	ccw_device_start() interface that takes a device specific channel program (one
149	or more CCWs) as input sets up the required architecture specific control blocks
150	and initiates an I/O request on behalf of the device driver. The
151	ccw_device_start() routine allows to specify whether it expects the CDS layer
152	to notify the device driver for every interrupt it observes, or with final status
153	only. See ccw_device_start() for more details. A device driver must never issue
154	ESA/390 I/O commands itself, but must use the Linux/390 CDS interfaces instead.
155	
156	For long running I/O request to be canceled, the CDS layer provides the
157	ccw_device_halt() function. Some devices require to initially issue a HALT
158	SUBCHANNEL (HSCH) command without having pending I/O requests. This function is
159	also covered by ccw_device_halt().
160	
161	
162	get_ciw() - get command information word
163	
164	This call enables a device driver to get information about supported commands
165	from the extended SenseID data.
166	
167	struct ciw *
168	ccw_device_get_ciw(struct ccw_device *cdev, __u32 cmd);
169	
170	cdev - The ccw_device for which the command is to be retrieved.
171	cmd  - The command type to be retrieved.
172	
173	ccw_device_get_ciw() returns:
174	NULL    - No extended data available, invalid device or command not found.
175	!NULL   - The command requested.
176	
177	
178	ccw_device_start() - Initiate I/O Request
179	
180	The ccw_device_start() routines is the I/O request front-end processor. All
181	device driver I/O requests must be issued using this routine. A device driver
182	must not issue ESA/390 I/O commands itself. Instead the ccw_device_start()
183	routine provides all interfaces required to drive arbitrary devices.
184	
185	This description also covers the status information passed to the device
186	driver's interrupt handler as this is related to the rules (flags) defined
187	with the associated I/O request when calling ccw_device_start().
188	
189	int ccw_device_start(struct ccw_device *cdev,
190			     struct ccw1 *cpa,
191			     unsigned long intparm,
192			     __u8 lpm,
193			     unsigned long flags);
194	int ccw_device_start_timeout(struct ccw_device *cdev,
195				     struct ccw1 *cpa,
196				     unsigned long intparm,
197				     __u8 lpm,
198				     unsigned long flags,
199				     int expires);
200	int ccw_device_start_key(struct ccw_device *cdev,
201				 struct ccw1 *cpa,
202				 unsigned long intparm,
203				 __u8 lpm,
204				 __u8 key,
205				 unsigned long flags);
206	int ccw_device_start_key_timeout(struct ccw_device *cdev,
207					 struct ccw1 *cpa,
208					 unsigned long intparm,
209					 __u8 lpm,
210					 __u8 key,
211					 unsigned long flags,
212					 int expires);
213	
214	cdev         : ccw_device the I/O is destined for
215	cpa          : logical start address of channel program
216	user_intparm : user specific interrupt information; will be presented
217		       back to the device driver's interrupt handler. Allows a
218	               device driver to associate the interrupt with a
219	               particular I/O request.
220	lpm          : defines the channel path to be used for a specific I/O
221	               request. A value of 0 will make cio use the opm.
222	key	     : the storage key to use for the I/O (useful for operating on a
223		       storage with a storage key != default key)
224	flag         : defines the action to be performed for I/O processing
225	expires      : timeout value in jiffies. The common I/O layer will terminate
226		       the running program after this and call the interrupt handler
227		       with ERR_PTR(-ETIMEDOUT) as irb.
228	
229	Possible flag values are :
230	
231	DOIO_ALLOW_SUSPEND       - channel program may become suspended
232	DOIO_DENY_PREFETCH       - don't allow for CCW prefetch; usually
233	                           this implies the channel program might
234	                           become modified
235	DOIO_SUPPRESS_INTER     - don't call the handler on intermediate status
236	
237	The cpa parameter points to the first format 1 CCW of a channel program :
238	
239	struct ccw1 {
240	      __u8  cmd_code;/* command code */
241	      __u8  flags;   /* flags, like IDA addressing, etc. */
242	      __u16 count;   /* byte count */
243	      __u32 cda;     /* data address */
244	} __attribute__ ((packed,aligned(8)));
245	
246	with the following CCW flags values defined :
247	
248	CCW_FLAG_DC        - data chaining
249	CCW_FLAG_CC        - command chaining
250	CCW_FLAG_SLI       - suppress incorrect length
251	CCW_FLAG_SKIP      - skip
252	CCW_FLAG_PCI       - PCI
253	CCW_FLAG_IDA       - indirect addressing
254	CCW_FLAG_SUSPEND   - suspend
255	
256	
257	Via ccw_device_set_options(), the device driver may specify the following
258	options for the device:
259	
260	DOIO_EARLY_NOTIFICATION  - allow for early interrupt notification
261	DOIO_REPORT_ALL          - report all interrupt conditions
262	
263	
264	The ccw_device_start() function returns :
265	
266	      0 - successful completion or request successfully initiated
267	-EBUSY	- The device is currently processing a previous I/O request, or there is
268	          a status pending at the device.
269	-ENODEV - cdev is invalid, the device is not operational or the ccw_device is
270	          not online.
271	
272	When the I/O request completes, the CDS first level interrupt handler will
273	accumulate the status in a struct irb and then call the device interrupt handler.
274	The intparm field will contain the value the device driver has associated with a 
275	particular I/O request. If a pending device status was recognized, 
276	intparm will be set to 0 (zero). This may happen during I/O initiation or delayed
277	by an alert status notification. In any case this status is not related to the
278	current (last) I/O request. In case of a delayed status notification no special
279	interrupt will be presented to indicate I/O completion as the I/O request was
280	never started, even though ccw_device_start() returned with successful completion.
281	
282	The irb may contain an error value, and the device driver should check for this
283	first:
284	
285	-ETIMEDOUT: the common I/O layer terminated the request after the specified
286	            timeout value
287	-EIO:       the common I/O layer terminated the request due to an error state
288	
289	If the concurrent sense flag in the extended status word (esw) in the irb is
290	set, the field erw.scnt in the esw describes the number of device specific
291	sense bytes available in the extended control word irb->scsw.ecw[]. No device
292	sensing by the device driver itself is required.
293	
294	The device interrupt handler can use the following definitions to investigate
295	the primary unit check source coded in sense byte 0 :
296	
297	SNS0_CMD_REJECT         0x80
298	SNS0_INTERVENTION_REQ   0x40
299	SNS0_BUS_OUT_CHECK      0x20
300	SNS0_EQUIPMENT_CHECK    0x10
301	SNS0_DATA_CHECK         0x08
302	SNS0_OVERRUN            0x04
303	SNS0_INCOMPL_DOMAIN     0x01
304	
305	Depending on the device status, multiple of those values may be set together.
306	Please refer to the device specific documentation for details.
307	
308	The irb->scsw.cstat field provides the (accumulated) subchannel status :
309	
310	SCHN_STAT_PCI            - program controlled interrupt
311	SCHN_STAT_INCORR_LEN     - incorrect length
312	SCHN_STAT_PROG_CHECK     - program check
313	SCHN_STAT_PROT_CHECK     - protection check
314	SCHN_STAT_CHN_DATA_CHK   - channel data check
315	SCHN_STAT_CHN_CTRL_CHK   - channel control check
316	SCHN_STAT_INTF_CTRL_CHK  - interface control check
317	SCHN_STAT_CHAIN_CHECK    - chaining check
318	
319	The irb->scsw.dstat field provides the (accumulated) device status :
320	
321	DEV_STAT_ATTENTION   - attention
322	DEV_STAT_STAT_MOD    - status modifier
323	DEV_STAT_CU_END      - control unit end
324	DEV_STAT_BUSY        - busy
325	DEV_STAT_CHN_END     - channel end
326	DEV_STAT_DEV_END     - device end
327	DEV_STAT_UNIT_CHECK  - unit check
328	DEV_STAT_UNIT_EXCEP  - unit exception
329	
330	Please see the ESA/390 Principles of Operation manual for details on the
331	individual flag meanings.
332	
333	Usage Notes :
334	
335	ccw_device_start() must be called disabled and with the ccw device lock held.
336	
337	The device driver is allowed to issue the next ccw_device_start() call from
338	within its interrupt handler already. It is not required to schedule a
339	bottom-half, unless a non deterministically long running error recovery procedure
340	or similar needs to be scheduled. During I/O processing the Linux/390 generic
341	I/O device driver support has already obtained the IRQ lock, i.e. the handler
342	must not try to obtain it again when calling ccw_device_start() or we end in a
343	deadlock situation!
344	
345	If a device driver relies on an I/O request to be completed prior to start the
346	next it can reduce I/O processing overhead by chaining a NoOp I/O command
347	CCW_CMD_NOOP to the end of the submitted CCW chain. This will force Channel-End
348	and Device-End status to be presented together, with a single interrupt.
349	However, this should be used with care as it implies the channel will remain
350	busy, not being able to process I/O requests for other devices on the same
351	channel. Therefore e.g. read commands should never use this technique, as the
352	result will be presented by a single interrupt anyway.
353	
354	In order to minimize I/O overhead, a device driver should use the
355	DOIO_REPORT_ALL  only if the device can report intermediate interrupt
356	information prior to device-end the device driver urgently relies on. In this
357	case all I/O interruptions are presented to the device driver until final
358	status is recognized.
359	
360	If a device is able to recover from asynchronously presented I/O errors, it can
361	perform overlapping I/O using the DOIO_EARLY_NOTIFICATION flag. While some
362	devices always report channel-end and device-end together, with a single
363	interrupt, others present primary status (channel-end) when the channel is
364	ready for the next I/O request and secondary status (device-end) when the data
365	transmission has been completed at the device.
366	
367	Above flag allows to exploit this feature, e.g. for communication devices that
368	can handle lost data on the network to allow for enhanced I/O processing.
369	
370	Unless the channel subsystem at any time presents a secondary status interrupt,
371	exploiting this feature will cause only primary status interrupts to be
372	presented to the device driver while overlapping I/O is performed. When a
373	secondary status without error (alert status) is presented, this indicates
374	successful completion for all overlapping ccw_device_start() requests that have
375	been issued since the last secondary (final) status.
376	
377	Channel programs that intend to set the suspend flag on a channel command word 
378	(CCW)  must start the I/O operation with the DOIO_ALLOW_SUSPEND option or the 
379	suspend flag will cause a channel program check. At the time the channel program 
380	becomes suspended an intermediate interrupt will be generated by the channel 
381	subsystem.
382	
383	ccw_device_resume() - Resume Channel Program Execution 
384	
385	If a device driver chooses to suspend the current channel program execution by 
386	setting the CCW suspend flag on a particular CCW, the channel program execution 
387	is suspended. In order to resume channel program execution the CIO layer 
388	provides the ccw_device_resume() routine. 
389	
390	int ccw_device_resume(struct ccw_device *cdev);
391	
392	cdev - ccw_device the resume operation is requested for
393	
394	The ccw_device_resume() function returns:
395	
396	        0  - suspended channel program is resumed
397	-EBUSY     - status pending
398	-ENODEV    - cdev invalid or not-operational subchannel 
399	-EINVAL    - resume function not applicable  
400	-ENOTCONN  - there is no I/O request pending for completion 
401	
402	Usage Notes:
403	Please have a look at the ccw_device_start() usage notes for more details on
404	suspended channel programs.
405	
406	ccw_device_halt() - Halt I/O Request Processing
407	
408	Sometimes a device driver might need a possibility to stop the processing of
409	a long-running channel program or the device might require to initially issue
410	a halt subchannel (HSCH) I/O command. For those purposes the ccw_device_halt()
411	command is provided.
412	
413	ccw_device_halt() must be called disabled and with the ccw device lock held.
414	
415	int ccw_device_halt(struct ccw_device *cdev,
416	                    unsigned long intparm);
417	
418	cdev    : ccw_device the halt operation is requested for
419	intparm : interruption parameter; value is only used if no I/O
420	          is outstanding, otherwise the intparm associated with
421	          the I/O request is returned
422	
423	The ccw_device_halt() function returns :
424	
425	      0 - request successfully initiated
426	-EBUSY  - the device is currently busy, or status pending.
427	-ENODEV - cdev invalid.
428	-EINVAL - The device is not operational or the ccw device is not online.
429	
430	Usage Notes :
431	
432	A device driver may write a never-ending channel program by writing a channel
433	program that at its end loops back to its beginning by means of a transfer in
434	channel (TIC)   command (CCW_CMD_TIC). Usually this is performed by network
435	device drivers by setting the PCI CCW flag (CCW_FLAG_PCI). Once this CCW is
436	executed a program controlled interrupt (PCI) is generated. The device driver
437	can then perform an appropriate action. Prior to interrupt of an outstanding
438	read to a network device (with or without PCI flag) a ccw_device_halt()
439	is required to end the pending operation.
440	
441	ccw_device_clear() - Terminage I/O Request Processing
442	
443	In order to terminate all I/O processing at the subchannel, the clear subchannel
444	(CSCH) command is used. It can be issued via ccw_device_clear().
445	
446	ccw_device_clear() must be called disabled and with the ccw device lock held.
447	
448	int ccw_device_clear(struct ccw_device *cdev, unsigned long intparm);
449	
450	cdev:	 ccw_device the clear operation is requested for
451	intparm: interruption parameter (see ccw_device_halt())
452	
453	The ccw_device_clear() function returns:
454	
455	      0 - request successfully initiated
456	-ENODEV - cdev invalid
457	-EINVAL - The device is not operational or the ccw device is not online.
458	
459	Miscellaneous Support Routines
460	
461	This chapter describes various routines to be used in a Linux/390 device
462	driver programming environment.
463	
464	get_ccwdev_lock()
465	
466	Get the address of the device specific lock. This is then used in
467	spin_lock() / spin_unlock() calls.
468	
469	
470	__u8 ccw_device_get_path_mask(struct ccw_device *cdev);
471	
472	Get the mask of the path currently available for cdev.
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