Documentation / DocBook / mtdnand.tmpl

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	<book id="MTD-NAND-Guide">
	 <bookinfo>
	  <title>MTD NAND Driver Programming Interface</title>
	  
	  <authorgroup>
	   <author>
	    <firstname>Thomas</firstname>
	    <surname>Gleixner</surname>
	    <affiliation>
	     <address>
	      <email>tglx[AT]linutronix[DOT]de</email>
	     </address>
	    </affiliation>
	   </author>
	  </authorgroup>
	
	  <copyright>
	   <year>2004</year>
	   <holder>Thomas Gleixner</holder>
	  </copyright>
	
	  <legalnotice>
	   <para>
	     This documentation is free software; you can redistribute
	     it and/or modify it under the terms of the GNU General Public
	     License version 2 as published by the Free Software Foundation.
	   </para>
	      
	   <para>
	     This program is distributed in the hope that it will be
	     useful, but WITHOUT ANY WARRANTY; without even the implied
	     warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
	     See the GNU General Public License for more details.
	   </para>
	      
	   <para>
	     You should have received a copy of the GNU General Public
	     License along with this program; if not, write to the Free
	     Software Foundation, Inc., 59 Temple Place, Suite 330, Boston,
	     MA 02111-1307 USA
	   </para>
	      
	   <para>
	     For more details see the file COPYING in the source
	     distribution of Linux.
	   </para>
	  </legalnotice>
	 </bookinfo>
	
	<toc></toc>
	
	  <chapter id="intro">
	      <title>Introduction</title>
	  <para>
	  	The generic NAND driver supports almost all NAND and AG-AND based
		chips and connects them to the Memory Technology Devices (MTD)
		subsystem of the Linux Kernel.
	  </para>
	  <para>
	  	This documentation is provided for developers who want to implement
		board drivers or filesystem drivers suitable for NAND devices.
	  </para>
	  </chapter>
	  
	  <chapter id="bugs">
	     <title>Known Bugs And Assumptions</title>
	  <para>
		None.	
	  </para>
	  </chapter>
	
	  <chapter id="dochints">
	     <title>Documentation hints</title>
	     <para>
	     The function and structure docs are autogenerated. Each function and 
	     struct member has a short description which is marked with an [XXX] identifier.
	     The following chapters explain the meaning of those identifiers.
	     </para>
	     <sect1 id="Function_identifiers_XXX">
		<title>Function identifiers [XXX]</title>
	     	<para>
		The functions are marked with [XXX] identifiers in the short
		comment. The identifiers explain the usage and scope of the
		functions. Following identifiers are used:
	     	</para>
		<itemizedlist>
			<listitem><para>
		  	[MTD Interface]</para><para>
			These functions provide the interface to the MTD kernel API. 
			They are not replacable and provide functionality
			which is complete hardware independent.
			</para></listitem>
			<listitem><para>
		  	[NAND Interface]</para><para>
			These functions are exported and provide the interface to the NAND kernel API. 
			</para></listitem>
			<listitem><para>
		  	[GENERIC]</para><para>
			Generic functions are not replacable and provide functionality
			which is complete hardware independent.
			</para></listitem>
			<listitem><para>
		  	[DEFAULT]</para><para>
			Default functions provide hardware related functionality which is suitable
			for most of the implementations. These functions can be replaced by the
			board driver if neccecary. Those functions are called via pointers in the
			NAND chip description structure. The board driver can set the functions which
			should be replaced by board dependent functions before calling nand_scan().
			If the function pointer is NULL on entry to nand_scan() then the pointer
			is set to the default function which is suitable for the detected chip type.
			</para></listitem>
		</itemizedlist>
	     </sect1>
	     <sect1 id="Struct_member_identifiers_XXX">
		<title>Struct member identifiers [XXX]</title>
	     	<para>
		The struct members are marked with [XXX] identifiers in the 
		comment. The identifiers explain the usage and scope of the
		members. Following identifiers are used:
	     	</para>
		<itemizedlist>
			<listitem><para>
		  	[INTERN]</para><para>
			These members are for NAND driver internal use only and must not be
			modified. Most of these values are calculated from the chip geometry
			information which is evaluated during nand_scan().
			</para></listitem>
			<listitem><para>
		  	[REPLACEABLE]</para><para>
			Replaceable members hold hardware related functions which can be 
			provided by the board driver. The board driver can set the functions which
			should be replaced by board dependent functions before calling nand_scan().
			If the function pointer is NULL on entry to nand_scan() then the pointer
			is set to the default function which is suitable for the detected chip type.
			</para></listitem>
			<listitem><para>
		  	[BOARDSPECIFIC]</para><para>
			Board specific members hold hardware related information which must
			be provided by the board driver. The board driver must set the function
			pointers and datafields before calling nand_scan().
			</para></listitem>
			<listitem><para>
		  	[OPTIONAL]</para><para>
			Optional members can hold information relevant for the board driver. The
			generic NAND driver code does not use this information.
			</para></listitem>
		</itemizedlist>
	     </sect1>
	  </chapter>   
	
	  <chapter id="basicboarddriver">
	     	<title>Basic board driver</title>
		<para>
			For most boards it will be sufficient to provide just the
			basic functions and fill out some really board dependent
			members in the nand chip description structure.
		</para>
		<sect1 id="Basic_defines">
			<title>Basic defines</title>
			<para>
				At least you have to provide a mtd structure and
				a storage for the ioremap'ed chip address.
				You can allocate the mtd structure using kmalloc
				or you can allocate it statically.
				In case of static allocation you have to allocate
				a nand_chip structure too.
			</para>
			<para>
				Kmalloc based example
			</para>
			<programlisting>
	static struct mtd_info *board_mtd;
	static unsigned long baseaddr;
			</programlisting>
			<para>
				Static example
			</para>
			<programlisting>
	static struct mtd_info board_mtd;
	static struct nand_chip board_chip;
	static unsigned long baseaddr;
			</programlisting>
		</sect1>
		<sect1 id="Partition_defines">
			<title>Partition defines</title>
			<para>
				If you want to divide your device into partitions, then
				enable the configuration switch CONFIG_MTD_PARTITIONS and define
				a partitioning scheme suitable to your board.
			</para>
			<programlisting>
	#define NUM_PARTITIONS 2
	static struct mtd_partition partition_info[] = {
		{ .name = "Flash partition 1",
		  .offset =  0,
		  .size =    8 * 1024 * 1024 },
		{ .name = "Flash partition 2",
		  .offset =  MTDPART_OFS_NEXT,
		  .size =    MTDPART_SIZ_FULL },
	};
			</programlisting>
		</sect1>
		<sect1 id="Hardware_control_functions">
			<title>Hardware control function</title>
			<para>
				The hardware control function provides access to the 
				control pins of the NAND chip(s). 
				The access can be done by GPIO pins or by address lines.
				If you use address lines, make sure that the timing
				requirements are met.
			</para>
			<para>
				<emphasis>GPIO based example</emphasis>
			</para>
			<programlisting>
	static void board_hwcontrol(struct mtd_info *mtd, int cmd)
	{
		switch(cmd){
			case NAND_CTL_SETCLE: /* Set CLE pin high */ break;
			case NAND_CTL_CLRCLE: /* Set CLE pin low */ break;
			case NAND_CTL_SETALE: /* Set ALE pin high */ break;
			case NAND_CTL_CLRALE: /* Set ALE pin low */ break;
			case NAND_CTL_SETNCE: /* Set nCE pin low */ break;
			case NAND_CTL_CLRNCE: /* Set nCE pin high */ break;
		}
	}
			</programlisting>
			<para>
				<emphasis>Address lines based example.</emphasis> It's assumed that the
				nCE pin is driven by a chip select decoder.
			</para>
			<programlisting>
	static void board_hwcontrol(struct mtd_info *mtd, int cmd)
	{
		struct nand_chip *this = (struct nand_chip *) mtd->priv;
		switch(cmd){
			case NAND_CTL_SETCLE: this->IO_ADDR_W |= CLE_ADRR_BIT;  break;
			case NAND_CTL_CLRCLE: this->IO_ADDR_W &amp;= ~CLE_ADRR_BIT; break;
			case NAND_CTL_SETALE: this->IO_ADDR_W |= ALE_ADRR_BIT;  break;
			case NAND_CTL_CLRALE: this->IO_ADDR_W &amp;= ~ALE_ADRR_BIT; break;
		}
	}
			</programlisting>
		</sect1>
		<sect1 id="Device_ready_function">
			<title>Device ready function</title>
			<para>
				If the hardware interface has the ready busy pin of the NAND chip connected to a
				GPIO or other accesible I/O pin, this function is used to read back the state of the
				pin. The function has no arguments and should return 0, if the device is busy (R/B pin 
				is low) and 1, if the device is ready (R/B pin is high).
				If the hardware interface does not give access to the ready busy pin, then
				the function must not be defined and the function pointer this->dev_ready is set to NULL.		
			</para>
		</sect1>
		<sect1 id="Init_function">
			<title>Init function</title>
			<para>
				The init function allocates memory and sets up all the board
				specific parameters and function pointers. When everything
				is set up nand_scan() is called. This function tries to
				detect and identify then chip. If a chip is found all the
				internal data fields are initialized accordingly.
				The structure(s) have to be zeroed out first and then filled with the neccecary 
				information about the device.
			</para>
			<programlisting>
	int __init board_init (void)
	{
		struct nand_chip *this;
		int err = 0;
	
		/* Allocate memory for MTD device structure and private data */
		board_mtd = kzalloc(sizeof(struct mtd_info) + sizeof(struct nand_chip), GFP_KERNEL);
		if (!board_mtd) {
			printk ("Unable to allocate NAND MTD device structure.\n");
			err = -ENOMEM;
			goto out;
		}
	
		/* map physical address */
		baseaddr = (unsigned long)ioremap(CHIP_PHYSICAL_ADDRESS, 1024);
		if(!baseaddr){
			printk("Ioremap to access NAND chip failed\n");
			err = -EIO;
			goto out_mtd;
		}
	
		/* Get pointer to private data */
		this = (struct nand_chip *) ();
		/* Link the private data with the MTD structure */
		board_mtd->priv = this;
	
		/* Set address of NAND IO lines */
		this->IO_ADDR_R = baseaddr;
		this->IO_ADDR_W = baseaddr;
		/* Reference hardware control function */
		this->hwcontrol = board_hwcontrol;
		/* Set command delay time, see datasheet for correct value */
		this->chip_delay = CHIP_DEPENDEND_COMMAND_DELAY;
		/* Assign the device ready function, if available */
		this->dev_ready = board_dev_ready;
		this->eccmode = NAND_ECC_SOFT;
	
		/* Scan to find existence of the device */
		if (nand_scan (board_mtd, 1)) {
			err = -ENXIO;
			goto out_ior;
		}
		
		add_mtd_partitions(board_mtd, partition_info, NUM_PARTITIONS);
		goto out;
	
	out_ior:
		iounmap((void *)baseaddr);
	out_mtd:
		kfree (board_mtd);
	out:
		return err;
	}
	module_init(board_init);
			</programlisting>
		</sect1>
		<sect1 id="Exit_function">
			<title>Exit function</title>
			<para>
				The exit function is only neccecary if the driver is
				compiled as a module. It releases all resources which
				are held by the chip driver and unregisters the partitions
				in the MTD layer.
			</para>
			<programlisting>
	#ifdef MODULE
	static void __exit board_cleanup (void)
	{
		/* Release resources, unregister device */
		nand_release (board_mtd);
	
		/* unmap physical address */
		iounmap((void *)baseaddr);
		
		/* Free the MTD device structure */
		kfree (board_mtd);
	}
	module_exit(board_cleanup);
	#endif
			</programlisting>
		</sect1>
	  </chapter>
	
	  <chapter id="boarddriversadvanced">
	     	<title>Advanced board driver functions</title>
		<para>
			This chapter describes the advanced functionality of the NAND
			driver. For a list of functions which can be overridden by the board
			driver see the documentation of the nand_chip structure.
		</para>
		<sect1 id="Multiple_chip_control">
			<title>Multiple chip control</title>
			<para>
				The nand driver can control chip arrays. Therefor the
				board driver must provide an own select_chip function. This
				function must (de)select the requested chip.
				The function pointer in the nand_chip structure must
				be set before calling nand_scan(). The maxchip parameter
				of nand_scan() defines the maximum number of chips to
				scan for. Make sure that the select_chip function can
				handle the requested number of chips.
			</para>
			<para>
				The nand driver concatenates the chips to one virtual
				chip and provides this virtual chip to the MTD layer.
			</para>
			<para>
				<emphasis>Note: The driver can only handle linear chip arrays
				of equally sized chips. There is no support for
				parallel arrays which extend the buswidth.</emphasis>
			</para>
			<para>
				<emphasis>GPIO based example</emphasis>
			</para>
			<programlisting>
	static void board_select_chip (struct mtd_info *mtd, int chip)
	{
		/* Deselect all chips, set all nCE pins high */
		GPIO(BOARD_NAND_NCE) |= 0xff;	
		if (chip >= 0)
			GPIO(BOARD_NAND_NCE) &amp;= ~ (1 &lt;&lt; chip);
	}
			</programlisting>
			<para>
				<emphasis>Address lines based example.</emphasis>
				Its assumed that the nCE pins are connected to an
				address decoder.
			</para>
			<programlisting>
	static void board_select_chip (struct mtd_info *mtd, int chip)
	{
		struct nand_chip *this = (struct nand_chip *) mtd->priv;
		
		/* Deselect all chips */
		this->IO_ADDR_R &amp;= ~BOARD_NAND_ADDR_MASK;
		this->IO_ADDR_W &amp;= ~BOARD_NAND_ADDR_MASK;
		switch (chip) {
		case 0:
			this->IO_ADDR_R |= BOARD_NAND_ADDR_CHIP0;
			this->IO_ADDR_W |= BOARD_NAND_ADDR_CHIP0;
			break;
		....	
		case n:
			this->IO_ADDR_R |= BOARD_NAND_ADDR_CHIPn;
			this->IO_ADDR_W |= BOARD_NAND_ADDR_CHIPn;
			break;
		}	
	}
			</programlisting>
		</sect1>
		<sect1 id="Hardware_ECC_support">
			<title>Hardware ECC support</title>
			<sect2 id="Functions_and_constants">
				<title>Functions and constants</title>
				<para>
					The nand driver supports three different types of
					hardware ECC.
					<itemizedlist>
					<listitem><para>NAND_ECC_HW3_256</para><para>
					Hardware ECC generator providing 3 bytes ECC per
					256 byte.
					</para>	</listitem>
					<listitem><para>NAND_ECC_HW3_512</para><para>
					Hardware ECC generator providing 3 bytes ECC per
					512 byte.
					</para>	</listitem>
					<listitem><para>NAND_ECC_HW6_512</para><para>
					Hardware ECC generator providing 6 bytes ECC per
					512 byte.
					</para>	</listitem>
					<listitem><para>NAND_ECC_HW8_512</para><para>
					Hardware ECC generator providing 6 bytes ECC per
					512 byte.
					</para>	</listitem>
					</itemizedlist>
					If your hardware generator has a different functionality
					add it at the appropriate place in nand_base.c
				</para>
				<para>
					The board driver must provide following functions:
					<itemizedlist>
					<listitem><para>enable_hwecc</para><para>
					This function is called before reading / writing to
					the chip. Reset or initialize the hardware generator
					in this function. The function is called with an
					argument which let you distinguish between read 
					and write operations.
					</para>	</listitem>
					<listitem><para>calculate_ecc</para><para>
					This function is called after read / write from / to
					the chip. Transfer the ECC from the hardware to
					the buffer. If the option NAND_HWECC_SYNDROME is set
					then the function is only called on write. See below.
					</para>	</listitem>
					<listitem><para>correct_data</para><para>
					In case of an ECC error this function is called for
					error detection and correction. Return 1 respectively 2
					in case the error can be corrected. If the error is
					not correctable return -1. If your hardware generator
					matches the default algorithm of the nand_ecc software
					generator then use the correction function provided
					by nand_ecc instead of implementing duplicated code.
					</para>	</listitem>
					</itemizedlist>
				</para>
			</sect2>
			<sect2 id="Hardware_ECC_with_syndrome_calculation">
			<title>Hardware ECC with syndrome calculation</title>
				<para>
					Many hardware ECC implementations provide Reed-Solomon
					codes and calculate an error syndrome on read. The syndrome
					must be converted to a standard Reed-Solomon syndrome
					before calling the error correction code in the generic
					Reed-Solomon library.
				</para>
				<para>
					The ECC bytes must be placed immidiately after the data
					bytes in order to make the syndrome generator work. This
					is contrary to the usual layout used by software ECC. The
					seperation of data and out of band area is not longer
					possible. The nand driver code handles this layout and
					the remaining free bytes in the oob area are managed by 
					the autoplacement code. Provide a matching oob-layout
					in this case. See rts_from4.c and diskonchip.c for 
					implementation reference. In those cases we must also
					use bad block tables on FLASH, because the ECC layout is
					interferring with the bad block marker positions.
					See bad block table support for details.
				</para>
			</sect2>
		</sect1>
		<sect1 id="Bad_Block_table_support">
			<title>Bad block table support</title>
			<para>
				Most NAND chips mark the bad blocks at a defined
				position in the spare area. Those blocks must 
				not be erased under any circumstances as the bad 
				block information would be lost.
				It is possible to check the bad block mark each
				time when the blocks are accessed by reading the
				spare area of the first page in the block. This
				is time consuming so a bad block table is used.
			</para>
			<para>
				The nand driver supports various types of bad block
				tables.
				<itemizedlist>
				<listitem><para>Per device</para><para>
				The bad block table contains all bad block information
				of the device which can consist of multiple chips.
				</para>	</listitem>
				<listitem><para>Per chip</para><para>
				A bad block table is used per chip and contains the
				bad block information for this particular chip.
				</para>	</listitem>
				<listitem><para>Fixed offset</para><para>
				The bad block table is located at a fixed offset
				in the chip (device). This applies to various
				DiskOnChip devices.
				</para>	</listitem>
				<listitem><para>Automatic placed</para><para>
				The bad block table is automatically placed and
				detected either at the end or at the beginning
				of a chip (device)
				</para>	</listitem>
				<listitem><para>Mirrored tables</para><para>
				The bad block table is mirrored on the chip (device) to
				allow updates of the bad block table without data loss.
				</para>	</listitem>
				</itemizedlist>
			</para>
			<para>	
				nand_scan() calls the function nand_default_bbt(). 
				nand_default_bbt() selects appropriate default
				bad block table desriptors depending on the chip information
				which was retrieved by nand_scan().
			</para>
			<para>
				The standard policy is scanning the device for bad 
				blocks and build a ram based bad block table which
				allows faster access than always checking the
				bad block information on the flash chip itself.
			</para>
			<sect2 id="Flash_based_tables">
				<title>Flash based tables</title>
				<para>
					It may be desired or neccecary to keep a bad block table in FLASH. 
					For AG-AND chips this is mandatory, as they have no factory marked
					bad blocks. They have factory marked good blocks. The marker pattern
					is erased when the block is erased to be reused. So in case of
					powerloss before writing the pattern back to the chip this block 
					would be lost and added to the bad blocks. Therefor we scan the 
					chip(s) when we detect them the first time for good blocks and 
					store this information in a bad block table before erasing any 
					of the blocks.
				</para>
				<para>
					The blocks in which the tables are stored are procteted against
					accidental access by marking them bad in the memory bad block
					table. The bad block table managment functions are allowed
					to circumvernt this protection.
				</para>
				<para>
					The simplest way to activate the FLASH based bad block table support 
					is to set the option NAND_USE_FLASH_BBT in the option field of
					the nand chip structure before calling nand_scan(). For AG-AND
					chips is this done by default.
					This activates the default FLASH based bad block table functionality 
					of the NAND driver. The default bad block table options are
					<itemizedlist>
					<listitem><para>Store bad block table per chip</para></listitem>
					<listitem><para>Use 2 bits per block</para></listitem>
					<listitem><para>Automatic placement at the end of the chip</para></listitem>
					<listitem><para>Use mirrored tables with version numbers</para></listitem>
					<listitem><para>Reserve 4 blocks at the end of the chip</para></listitem>
					</itemizedlist>
				</para>
			</sect2>
			<sect2 id="User_defined_tables">
				<title>User defined tables</title>
				<para>
					User defined tables are created by filling out a 
					nand_bbt_descr structure and storing the pointer in the
					nand_chip structure member bbt_td before calling nand_scan(). 
					If a mirror table is neccecary a second structure must be
					created and a pointer to this structure must be stored
					in bbt_md inside the nand_chip structure. If the bbt_md 
					member is set to NULL then only the main table is used
					and no scan for the mirrored table is performed.
				</para>
				<para>
					The most important field in the nand_bbt_descr structure
					is the options field. The options define most of the 
					table properties. Use the predefined constants from
					nand.h to define the options.
					<itemizedlist>
					<listitem><para>Number of bits per block</para>
					<para>The supported number of bits is 1, 2, 4, 8.</para></listitem>
					<listitem><para>Table per chip</para>
					<para>Setting the constant NAND_BBT_PERCHIP selects that
					a bad block table is managed for each chip in a chip array.
					If this option is not set then a per device bad block table
					is used.</para></listitem>
					<listitem><para>Table location is absolute</para>
					<para>Use the option constant NAND_BBT_ABSPAGE and
					define the absolute page number where the bad block
					table starts in the field pages. If you have selected bad block
					tables per chip and you have a multi chip array then the start page
					must be given for each chip in the chip array. Note: there is no scan
					for a table ident pattern performed, so the fields 
					pattern, veroffs, offs, len can be left uninitialized</para></listitem>
					<listitem><para>Table location is automatically detected</para>
					<para>The table can either be located in the first or the last good
					blocks of the chip (device). Set NAND_BBT_LASTBLOCK to place
					the bad block table at the end of the chip (device). The
					bad block tables are marked and identified by a pattern which
					is stored in the spare area of the first page in the block which
					holds the bad block table. Store a pointer to the pattern  
					in the pattern field. Further the length of the pattern has to be 
					stored in len and the offset in the spare area must be given
					in the offs member of the nand_bbt_descr stucture. For mirrored
					bad block tables different patterns are mandatory.</para></listitem>
					<listitem><para>Table creation</para>
					<para>Set the option NAND_BBT_CREATE to enable the table creation
					if no table can be found during the scan. Usually this is done only 
					once if a new chip is found. </para></listitem>
					<listitem><para>Table write support</para>
					<para>Set the option NAND_BBT_WRITE to enable the table write support.
					This allows the update of the bad block table(s) in case a block has
					to be marked bad due to wear. The MTD interface function block_markbad
					is calling the update function of the bad block table. If the write
					support is enabled then the table is updated on FLASH.</para>
					<para>
					Note: Write support should only be enabled for mirrored tables with
					version control.
					</para></listitem>
					<listitem><para>Table version control</para>
					<para>Set the option NAND_BBT_VERSION to enable the table version control.
					It's highly recommended to enable this for mirrored tables with write
					support. It makes sure that the risk of loosing the bad block
					table information is reduced to the loss of the information about the
					one worn out block which should be marked bad. The version is stored in
					4 consecutive bytes in the spare area of the device. The position of
					the version number is defined by the member veroffs in the bad block table
					descriptor.</para></listitem>
					<listitem><para>Save block contents on write</para>
					<para>
					In case that the block which holds the bad block table does contain
					other useful information, set the option NAND_BBT_SAVECONTENT. When
					the bad block table is written then the whole block is read the bad
					block table is updated and the block is erased and everything is 
					written back. If this option is not set only the bad block table
					is written and everything else in the block is ignored and erased.
					</para></listitem>
					<listitem><para>Number of reserved blocks</para>
					<para>
					For automatic placement some blocks must be reserved for
					bad block table storage. The number of reserved blocks is defined 
					in the maxblocks member of the babd block table description structure.
					Reserving 4 blocks for mirrored tables should be a reasonable number. 
					This also limits the number of blocks which are scanned for the bad
					block table ident pattern.
					</para></listitem>
					</itemizedlist>
				</para>
			</sect2>
		</sect1>
		<sect1 id="Spare_area_placement">
			<title>Spare area (auto)placement</title>
			<para>
				The nand driver implements different possibilities for
				placement of filesystem data in the spare area, 
				<itemizedlist>
				<listitem><para>Placement defined by fs driver</para></listitem>
				<listitem><para>Automatic placement</para></listitem>
				</itemizedlist>
				The default placement function is automatic placement. The
				nand driver has built in default placement schemes for the
				various chiptypes. If due to hardware ECC functionality the
				default placement does not fit then the board driver can
				provide a own placement scheme.
			</para>
			<para>
				File system drivers can provide a own placement scheme which
				is used instead of the default placement scheme.
			</para>
			<para>
				Placement schemes are defined by a nand_oobinfo structure
		     		<programlisting>
	struct nand_oobinfo {
		int	useecc;
		int	eccbytes;
		int	eccpos[24];
		int	oobfree[8][2];
	};
		     		</programlisting>
				<itemizedlist>
				<listitem><para>useecc</para><para>
					The useecc member controls the ecc and placement function. The header
					file include/mtd/mtd-abi.h contains constants to select ecc and
					placement. MTD_NANDECC_OFF switches off the ecc complete. This is
					not recommended and available for testing and diagnosis only.
					MTD_NANDECC_PLACE selects caller defined placement, MTD_NANDECC_AUTOPLACE
					selects automatic placement.
				</para></listitem>
				<listitem><para>eccbytes</para><para>
					The eccbytes member defines the number of ecc bytes per page.
				</para></listitem>
				<listitem><para>eccpos</para><para>
					The eccpos array holds the byte offsets in the spare area where
					the ecc codes are placed.
				</para></listitem>
				<listitem><para>oobfree</para><para>
					The oobfree array defines the areas in the spare area which can be
					used for automatic placement. The information is given in the format
					{offset, size}. offset defines the start of the usable area, size the
					length in bytes. More than one area can be defined. The list is terminated
					by an {0, 0} entry.
				</para></listitem>
				</itemizedlist>
			</para>
			<sect2 id="Placement_defined_by_fs_driver">
				<title>Placement defined by fs driver</title>
				<para>
					The calling function provides a pointer to a nand_oobinfo
					structure which defines the ecc placement. For writes the
					caller must provide a spare area buffer along with the
					data buffer. The spare area buffer size is (number of pages) *
					(size of spare area). For reads the buffer size is
					(number of pages) * ((size of spare area) + (number of ecc
					steps per page) * sizeof (int)). The driver stores the
					result of the ecc check for each tuple in the spare buffer.
					The storage sequence is 
				</para>
				<para>
					&lt;spare data page 0&gt;&lt;ecc result 0&gt;...&lt;ecc result n&gt;
				</para>
				<para>
					...
				</para>
				<para>
					&lt;spare data page n&gt;&lt;ecc result 0&gt;...&lt;ecc result n&gt;
				</para>
				<para>
					This is a legacy mode used by YAFFS1.
				</para>
				<para>
					If the spare area buffer is NULL then only the ECC placement is
					done according to the given scheme in the nand_oobinfo structure.
				</para>
			</sect2>
			<sect2 id="Automatic_placement">
				<title>Automatic placement</title>
				<para>
					Automatic placement uses the built in defaults to place the
					ecc bytes in the spare area. If filesystem data have to be stored /
					read into the spare area then the calling function must provide a
					buffer. The buffer size per page is determined by the oobfree array in
					the nand_oobinfo structure.
				</para>
				<para>
					If the spare area buffer is NULL then only the ECC placement is
					done according to the default builtin scheme.
				</para>
			</sect2>
			<sect2 id="User_space_placement_selection">
				<title>User space placement selection</title>
			<para>
				All non ecc functions like mtd->read and mtd->write use an internal 
				structure, which can be set by an ioctl. This structure is preset 
				to the autoplacement default.
		     		<programlisting>
		ioctl (fd, MEMSETOOBSEL, oobsel);
		     		</programlisting>
				oobsel is a pointer to a user supplied structure of type
				nand_oobconfig. The contents of this structure must match the 
				criteria of the filesystem, which will be used. See an example in utils/nandwrite.c.
			</para>
			</sect2>
		</sect1>	
		<sect1 id="Spare_area_autoplacement_default">
			<title>Spare area autoplacement default schemes</title>
			<sect2 id="pagesize_256">
				<title>256 byte pagesize</title>
	<informaltable><tgroup cols="3"><tbody>
	<row>
	<entry>Offset</entry>
	<entry>Content</entry>
	<entry>Comment</entry>
	</row>
	<row>
	<entry>0x00</entry>
	<entry>ECC byte 0</entry>
	<entry>Error correction code byte 0</entry>
	</row>
	<row>
	<entry>0x01</entry>
	<entry>ECC byte 1</entry>
	<entry>Error correction code byte 1</entry>
	</row>
	<row>
	<entry>0x02</entry>
	<entry>ECC byte 2</entry>
	<entry>Error correction code byte 2</entry>
	</row>
	<row>
	<entry>0x03</entry>
	<entry>Autoplace 0</entry>
	<entry></entry>
	</row>
	<row>
	<entry>0x04</entry>
	<entry>Autoplace 1</entry>
	<entry></entry>
	</row>
	<row>
	<entry>0x05</entry>
	<entry>Bad block marker</entry>
	<entry>If any bit in this byte is zero, then this block is bad.
	This applies only to the first page in a block. In the remaining
	pages this byte is reserved</entry>
	</row>
	<row>
	<entry>0x06</entry>
	<entry>Autoplace 2</entry>
	<entry></entry>
	</row>
	<row>
	<entry>0x07</entry>
	<entry>Autoplace 3</entry>
	<entry></entry>
	</row>
	</tbody></tgroup></informaltable>
			</sect2>
			<sect2 id="pagesize_512">
				<title>512 byte pagesize</title>
	<informaltable><tgroup cols="3"><tbody>
	<row>
	<entry>Offset</entry>
	<entry>Content</entry>
	<entry>Comment</entry>
	</row>
	<row>
	<entry>0x00</entry>
	<entry>ECC byte 0</entry>
	<entry>Error correction code byte 0 of the lower 256 Byte data in
	this page</entry>
	</row>
	<row>
	<entry>0x01</entry>
	<entry>ECC byte 1</entry>
	<entry>Error correction code byte 1 of the lower 256 Bytes of data
	in this page</entry>
	</row>
	<row>
	<entry>0x02</entry>
	<entry>ECC byte 2</entry>
	<entry>Error correction code byte 2 of the lower 256 Bytes of data
	in this page</entry>
	</row>
	<row>
	<entry>0x03</entry>
	<entry>ECC byte 3</entry>
	<entry>Error correction code byte 0 of the upper 256 Bytes of data
	in this page</entry>
	</row>
	<row>
	<entry>0x04</entry>
	<entry>reserved</entry>
	<entry>reserved</entry>
	</row>
	<row>
	<entry>0x05</entry>
	<entry>Bad block marker</entry>
	<entry>If any bit in this byte is zero, then this block is bad.
	This applies only to the first page in a block. In the remaining
	pages this byte is reserved</entry>
	</row>
	<row>
	<entry>0x06</entry>
	<entry>ECC byte 4</entry>
	<entry>Error correction code byte 1 of the upper 256 Bytes of data
	in this page</entry>
	</row>
	<row>
	<entry>0x07</entry>
	<entry>ECC byte 5</entry>
	<entry>Error correction code byte 2 of the upper 256 Bytes of data
	in this page</entry>
	</row>
	<row>
	<entry>0x08 - 0x0F</entry>
	<entry>Autoplace 0 - 7</entry>
	<entry></entry>
	</row>
	</tbody></tgroup></informaltable>
			</sect2>
			<sect2 id="pagesize_2048">
				<title>2048 byte pagesize</title>
	<informaltable><tgroup cols="3"><tbody>
	<row>
	<entry>Offset</entry>
	<entry>Content</entry>
	<entry>Comment</entry>
	</row>
	<row>
	<entry>0x00</entry>
	<entry>Bad block marker</entry>
	<entry>If any bit in this byte is zero, then this block is bad.
	This applies only to the first page in a block. In the remaining
	pages this byte is reserved</entry>
	</row>
	<row>
	<entry>0x01</entry>
	<entry>Reserved</entry>
	<entry>Reserved</entry>
	</row>
	<row>
	<entry>0x02-0x27</entry>
	<entry>Autoplace 0 - 37</entry>
	<entry></entry>
	</row>
	<row>
	<entry>0x28</entry>
	<entry>ECC byte 0</entry>
	<entry>Error correction code byte 0 of the first 256 Byte data in
	this page</entry>
	</row>
	<row>
	<entry>0x29</entry>
	<entry>ECC byte 1</entry>
	<entry>Error correction code byte 1 of the first 256 Bytes of data
	in this page</entry>
	</row>
	<row>
	<entry>0x2A</entry>
	<entry>ECC byte 2</entry>
	<entry>Error correction code byte 2 of the first 256 Bytes data in
	this page</entry>
	</row>
	<row>
	<entry>0x2B</entry>
	<entry>ECC byte 3</entry>
	<entry>Error correction code byte 0 of the second 256 Bytes of data
	in this page</entry>
	</row>
	<row>
	<entry>0x2C</entry>
	<entry>ECC byte 4</entry>
	<entry>Error correction code byte 1 of the second 256 Bytes of data
	in this page</entry>
	</row>
	<row>
	<entry>0x2D</entry>
	<entry>ECC byte 5</entry>
	<entry>Error correction code byte 2 of the second 256 Bytes of data
	in this page</entry>
	</row>
	<row>
	<entry>0x2E</entry>
	<entry>ECC byte 6</entry>
	<entry>Error correction code byte 0 of the third 256 Bytes of data
	in this page</entry>
	</row>
	<row>
	<entry>0x2F</entry>
	<entry>ECC byte 7</entry>
	<entry>Error correction code byte 1 of the third 256 Bytes of data
	in this page</entry>
	</row>
	<row>
	<entry>0x30</entry>
	<entry>ECC byte 8</entry>
	<entry>Error correction code byte 2 of the third 256 Bytes of data
	in this page</entry>
	</row>
	<row>
	<entry>0x31</entry>
	<entry>ECC byte 9</entry>
	<entry>Error correction code byte 0 of the fourth 256 Bytes of data
	in this page</entry>
	</row>
	<row>
	<entry>0x32</entry>
	<entry>ECC byte 10</entry>
	<entry>Error correction code byte 1 of the fourth 256 Bytes of data
	in this page</entry>
	</row>
	<row>
	<entry>0x33</entry>
	<entry>ECC byte 11</entry>
	<entry>Error correction code byte 2 of the fourth 256 Bytes of data
	in this page</entry>
	</row>
	<row>
	<entry>0x34</entry>
	<entry>ECC byte 12</entry>
	<entry>Error correction code byte 0 of the fifth 256 Bytes of data
	in this page</entry>
	</row>
	<row>
	<entry>0x35</entry>
	<entry>ECC byte 13</entry>
	<entry>Error correction code byte 1 of the fifth 256 Bytes of data
	in this page</entry>
	</row>
	<row>
	<entry>0x36</entry>
	<entry>ECC byte 14</entry>
	<entry>Error correction code byte 2 of the fifth 256 Bytes of data
	in this page</entry>
	</row>
	<row>
	<entry>0x37</entry>
	<entry>ECC byte 15</entry>
	<entry>Error correction code byte 0 of the sixt 256 Bytes of data
	in this page</entry>
	</row>
	<row>
	<entry>0x38</entry>
	<entry>ECC byte 16</entry>
	<entry>Error correction code byte 1 of the sixt 256 Bytes of data
	in this page</entry>
	</row>
	<row>
	<entry>0x39</entry>
	<entry>ECC byte 17</entry>
	<entry>Error correction code byte 2 of the sixt 256 Bytes of data
	in this page</entry>
	</row>
	<row>
	<entry>0x3A</entry>
	<entry>ECC byte 18</entry>
	<entry>Error correction code byte 0 of the seventh 256 Bytes of
	data in this page</entry>
	</row>
	<row>
	<entry>0x3B</entry>
	<entry>ECC byte 19</entry>
	<entry>Error correction code byte 1 of the seventh 256 Bytes of
	data in this page</entry>
	</row>
	<row>
	<entry>0x3C</entry>
	<entry>ECC byte 20</entry>
	<entry>Error correction code byte 2 of the seventh 256 Bytes of
	data in this page</entry>
	</row>
	<row>
	<entry>0x3D</entry>
	<entry>ECC byte 21</entry>
	<entry>Error correction code byte 0 of the eigth 256 Bytes of data
	in this page</entry>
	</row>
	<row>
	<entry>0x3E</entry>
	<entry>ECC byte 22</entry>
	<entry>Error correction code byte 1 of the eigth 256 Bytes of data
	in this page</entry>
	</row>
	<row>
	<entry>0x3F</entry>
	<entry>ECC byte 23</entry>
	<entry>Error correction code byte 2 of the eigth 256 Bytes of data
	in this page</entry>
	</row>
	</tbody></tgroup></informaltable>
			</sect2>
	     	</sect1>
	  </chapter>
	
	  <chapter id="filesystems">
	     	<title>Filesystem support</title>
		<para>
			The NAND driver provides all neccecary functions for a
			filesystem via the MTD interface.
		</para>
		<para>
			Filesystems must be aware of the NAND pecularities and
			restrictions. One major restrictions of NAND Flash is, that you cannot 
			write as often as you want to a page. The consecutive writes to a page, 
			before erasing it again, are restricted to 1-3 writes, depending on the 
			manufacturers specifications. This applies similar to the spare area. 
		</para>
		<para>
			Therefor NAND aware filesystems must either write in page size chunks
			or hold a writebuffer to collect smaller writes until they sum up to 
			pagesize. Available NAND aware filesystems: JFFS2, YAFFS. 		
		</para>
		<para>
			The spare area usage to store filesystem data is controlled by
			the spare area placement functionality which is described in one
			of the earlier chapters.
		</para>
	  </chapter>	
	  <chapter id="tools">
	     	<title>Tools</title>
		<para>
			The MTD project provides a couple of helpful tools to handle NAND Flash.
			<itemizedlist>
			<listitem><para>flasherase, flasheraseall: Erase and format FLASH partitions</para></listitem>
			<listitem><para>nandwrite: write filesystem images to NAND FLASH</para></listitem>
			<listitem><para>nanddump: dump the contents of a NAND FLASH partitions</para></listitem>
			</itemizedlist>
		</para>
		<para>
			These tools are aware of the NAND restrictions. Please use those tools
			instead of complaining about errors which are caused by non NAND aware
			access methods.
		</para>
	  </chapter>	
	
	  <chapter id="defines">
	     <title>Constants</title>
	     <para>
	     This chapter describes the constants which might be relevant for a driver developer.
	     </para>
	     <sect1 id="Chip_option_constants">
		<title>Chip option constants</title>
	     	<sect2 id="Constants_for_chip_id_table">
			<title>Constants for chip id table</title>
	     		<para>
			These constants are defined in nand.h. They are ored together to describe
			the chip functionality.
	     		<programlisting>
	/* Chip can not auto increment pages */
	#define NAND_NO_AUTOINCR	0x00000001
	/* Buswitdh is 16 bit */
	#define NAND_BUSWIDTH_16	0x00000002
	/* Device supports partial programming without padding */
	#define NAND_NO_PADDING		0x00000004
	/* Chip has cache program function */
	#define NAND_CACHEPRG		0x00000008
	/* Chip has copy back function */
	#define NAND_COPYBACK		0x00000010
	/* AND Chip which has 4 banks and a confusing page / block 
	 * assignment. See Renesas datasheet for further information */
	#define NAND_IS_AND		0x00000020
	/* Chip has a array of 4 pages which can be read without
	 * additional ready /busy waits */
	#define NAND_4PAGE_ARRAY	0x00000040 
			</programlisting>
	     		</para>
	     	</sect2>
	     	<sect2 id="Constants_for_runtime_options">
			<title>Constants for runtime options</title>
	     		<para>
			These constants are defined in nand.h. They are ored together to describe
			the functionality.
	     		<programlisting>
	/* Use a flash based bad block table. This option is parsed by the
	 * default bad block table function (nand_default_bbt). */
	#define NAND_USE_FLASH_BBT	0x00010000
	/* The hw ecc generator provides a syndrome instead a ecc value on read 
	 * This can only work if we have the ecc bytes directly behind the 
	 * data bytes. Applies for DOC and AG-AND Renesas HW Reed Solomon generators */
	#define NAND_HWECC_SYNDROME	0x00020000
			</programlisting>
	     		</para>
	     	</sect2>
	     </sect1>	
	
	     <sect1 id="EEC_selection_constants">
		<title>ECC selection constants</title>
		<para>
		Use these constants to select the ECC algorithm.
	  	<programlisting>
	/* No ECC. Usage is not recommended ! */
	#define NAND_ECC_NONE		0
	/* Software ECC 3 byte ECC per 256 Byte data */
	#define NAND_ECC_SOFT		1
	/* Hardware ECC 3 byte ECC per 256 Byte data */
	#define NAND_ECC_HW3_256	2
	/* Hardware ECC 3 byte ECC per 512 Byte data */
	#define NAND_ECC_HW3_512	3
	/* Hardware ECC 6 byte ECC per 512 Byte data */
	#define NAND_ECC_HW6_512	4
	/* Hardware ECC 6 byte ECC per 512 Byte data */
	#define NAND_ECC_HW8_512	6
		</programlisting>
		</para>
	     </sect1>	
	
	     <sect1 id="Hardware_control_related_constants">
		<title>Hardware control related constants</title>
		<para>
		These constants describe the requested hardware access function when
		the boardspecific hardware control function is called
	  	<programlisting>
	/* Select the chip by setting nCE to low */
	#define NAND_CTL_SETNCE 	1
	/* Deselect the chip by setting nCE to high */
	#define NAND_CTL_CLRNCE		2
	/* Select the command latch by setting CLE to high */
	#define NAND_CTL_SETCLE		3
	/* Deselect the command latch by setting CLE to low */
	#define NAND_CTL_CLRCLE		4
	/* Select the address latch by setting ALE to high */
	#define NAND_CTL_SETALE		5
	/* Deselect the address latch by setting ALE to low */
	#define NAND_CTL_CLRALE		6
	/* Set write protection by setting WP to high. Not used! */
	#define NAND_CTL_SETWP		7
	/* Clear write protection by setting WP to low. Not used! */
	#define NAND_CTL_CLRWP		8
		</programlisting>
		</para>
	     </sect1>	
	
	     <sect1 id="Bad_block_table_constants">
		<title>Bad block table related constants</title>
		<para>
		These constants describe the options used for bad block
		table descriptors.
	  	<programlisting>
	/* Options for the bad block table descriptors */
	
	/* The number of bits used per block in the bbt on the device */
	#define NAND_BBT_NRBITS_MSK	0x0000000F
	#define NAND_BBT_1BIT		0x00000001
	#define NAND_BBT_2BIT		0x00000002
	#define NAND_BBT_4BIT		0x00000004
	#define NAND_BBT_8BIT		0x00000008
	/* The bad block table is in the last good block of the device */
	#define	NAND_BBT_LASTBLOCK	0x00000010
	/* The bbt is at the given page, else we must scan for the bbt */
	#define NAND_BBT_ABSPAGE	0x00000020
	/* The bbt is at the given page, else we must scan for the bbt */
	#define NAND_BBT_SEARCH		0x00000040
	/* bbt is stored per chip on multichip devices */
	#define NAND_BBT_PERCHIP	0x00000080
	/* bbt has a version counter at offset veroffs */
	#define NAND_BBT_VERSION	0x00000100
	/* Create a bbt if none axists */
	#define NAND_BBT_CREATE		0x00000200
	/* Search good / bad pattern through all pages of a block */
	#define NAND_BBT_SCANALLPAGES	0x00000400
	/* Scan block empty during good / bad block scan */
	#define NAND_BBT_SCANEMPTY	0x00000800
	/* Write bbt if neccecary */
	#define NAND_BBT_WRITE		0x00001000
	/* Read and write back block contents when writing bbt */
	#define NAND_BBT_SAVECONTENT	0x00002000
		</programlisting>
		</para>
	     </sect1>	
	
	  </chapter>
	  	
	  <chapter id="structs">
	     <title>Structures</title>
	     <para>
	     This chapter contains the autogenerated documentation of the structures which are
	     used in the NAND driver and might be relevant for a driver developer. Each  
	     struct member has a short description which is marked with an [XXX] identifier.
	     See the chapter "Documentation hints" for an explanation.
	     </para>
	!Iinclude/linux/mtd/nand.h
	  </chapter>
	
	  <chapter id="pubfunctions">
	     <title>Public Functions Provided</title>
	     <para>
	     This chapter contains the autogenerated documentation of the NAND kernel API functions
	      which are exported. Each function has a short description which is marked with an [XXX] identifier.
	     See the chapter "Documentation hints" for an explanation.
	     </para>
	!Edrivers/mtd/nand/nand_base.c
	!Edrivers/mtd/nand/nand_bbt.c
	!Edrivers/mtd/nand/nand_ecc.c
	  </chapter>
	  
	  <chapter id="intfunctions">
	     <title>Internal Functions Provided</title>
	     <para>
	     This chapter contains the autogenerated documentation of the NAND driver internal functions.
	     Each function has a short description which is marked with an [XXX] identifier.
	     See the chapter "Documentation hints" for an explanation.
	     The functions marked with [DEFAULT] might be relevant for a board driver developer.
	     </para>
	!Idrivers/mtd/nand/nand_base.c
	!Idrivers/mtd/nand/nand_bbt.c
	<!-- No internal functions for kernel-doc:
	X!Idrivers/mtd/nand/nand_ecc.c
	-->
	  </chapter>
	
	  <chapter id="credits">
	     <title>Credits</title>
		<para>
			The following people have contributed to the NAND driver:
			<orderedlist>
				<listitem><para>Steven J. Hill<email>sjhill[AT]realitydiluted[DOT]com</email></para></listitem>
				<listitem><para>David Woodhouse<email>dwmw2[AT]infradead[DOT]org</email></para></listitem>
				<listitem><para>Thomas Gleixner<email>tglx[AT]linutronix[DOT]de</email></para></listitem>
			</orderedlist>
			A lot of users have provided bugfixes, improvements and helping hands for testing.
			Thanks a lot.
		</para>
		<para>
			The following people have contributed to this document:
			<orderedlist>
				<listitem><para>Thomas Gleixner<email>tglx[AT]linutronix[DOT]de</email></para></listitem>
			</orderedlist>