block: directly insert blk-mq request from blk_insert_cloned_request()

[mirror_ubuntu-bionic-kernel.git] / Documentation / driver-api / mtdnand.rst

=====================================
MTD NAND Driver Programming Interface
=====================================

:Author: Thomas Gleixner

Introduction
============

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.

This documentation is provided for developers who want to implement
board drivers or filesystem drivers suitable for NAND devices.

Known Bugs And Assumptions
==========================

None.

Documentation hints
===================

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.

Function identifiers [XXX]
--------------------------

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:

-  [MTD Interface]

   These functions provide the interface to the MTD kernel API. They are
   not replaceable and provide functionality which is complete hardware
   independent.

-  [NAND Interface]

   These functions are exported and provide the interface to the NAND
   kernel API.

-  [GENERIC]

   Generic functions are not replaceable and provide functionality which
   is complete hardware independent.

-  [DEFAULT]

   Default functions provide hardware related functionality which is
   suitable for most of the implementations. These functions can be
   replaced by the board driver if necessary. 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.

Struct member identifiers [XXX]
-------------------------------

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:

-  [INTERN]

   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().

-  [REPLACEABLE]

   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.

-  [BOARDSPECIFIC]

   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().

-  [OPTIONAL]

   Optional members can hold information relevant for the board driver.
   The generic NAND driver code does not use this information.

Basic board driver
==================

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.

Basic defines
-------------

At least you have to provide a nand_chip structure and a storage for
the ioremap'ed chip address. You can allocate the nand_chip structure
using kmalloc or you can allocate it statically. The NAND chip structure
embeds an mtd structure which will be registered to the MTD subsystem.
You can extract a pointer to the mtd structure from a nand_chip pointer
using the nand_to_mtd() helper.

Kmalloc based example

::

    static struct mtd_info *board_mtd;
    static void __iomem *baseaddr;


Static example

::

    static struct nand_chip board_chip;
    static void __iomem *baseaddr;


Partition defines
-----------------

If you want to divide your device into partitions, then define a
partitioning scheme suitable to your board.

::

    #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 },
    };


Hardware control function
-------------------------

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.

*GPIO based example*

::

    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;
        }
    }


*Address lines based example.* It's assumed that the nCE pin is driven
by a chip select decoder.

::

    static void board_hwcontrol(struct mtd_info *mtd, int cmd)
    {
        struct nand_chip *this = mtd_to_nand(mtd);
        switch(cmd){
            case NAND_CTL_SETCLE: this->IO_ADDR_W |= CLE_ADRR_BIT;  break;
            case NAND_CTL_CLRCLE: this->IO_ADDR_W &= ~CLE_ADRR_BIT; break;
            case NAND_CTL_SETALE: this->IO_ADDR_W |= ALE_ADRR_BIT;  break;
            case NAND_CTL_CLRALE: this->IO_ADDR_W &= ~ALE_ADRR_BIT; break;
        }
    }


Device ready function
---------------------

If the hardware interface has the ready busy pin of the NAND chip
connected to a GPIO or other accessible 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.

Init function
-------------

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
necessary information about the device.

::

    static int __init board_init (void)
    {
        struct nand_chip *this;
        int err = 0;

        /* Allocate memory for MTD device structure and private data */
        this = kzalloc(sizeof(struct nand_chip), GFP_KERNEL);
        if (!this) {
            printk ("Unable to allocate NAND MTD device structure.\n");
            err = -ENOMEM;
            goto out;
        }

        board_mtd = nand_to_mtd(this);

        /* map physical address */
        baseaddr = ioremap(CHIP_PHYSICAL_ADDRESS, 1024);
        if (!baseaddr) {
            printk("Ioremap to access NAND chip failed\n");
            err = -EIO;
            goto out_mtd;
        }

        /* 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(baseaddr);
    out_mtd:
        kfree (this);
    out:
        return err;
    }
    module_init(board_init);


Exit function
-------------

The exit function is only necessary 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.

::

    #ifdef MODULE
    static void __exit board_cleanup (void)
    {
        /* Release resources, unregister device */
        nand_release (board_mtd);

        /* unmap physical address */
        iounmap(baseaddr);

        /* Free the MTD device structure */
        kfree (mtd_to_nand(board_mtd));
    }
    module_exit(board_cleanup);
    #endif


Advanced board driver functions
===============================

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.

Multiple chip control
---------------------

The nand driver can control chip arrays. Therefore 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.

The nand driver concatenates the chips to one virtual chip and provides
this virtual chip to the MTD layer.

*Note: The driver can only handle linear chip arrays of equally sized
chips. There is no support for parallel arrays which extend the
buswidth.*

*GPIO based example*

::

    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) &= ~ (1 << chip);
    }


*Address lines based example.* Its assumed that the nCE pins are
connected to an address decoder.

::

    static void board_select_chip (struct mtd_info *mtd, int chip)
    {
        struct nand_chip *this = mtd_to_nand(mtd);

        /* Deselect all chips */
        this->IO_ADDR_R &= ~BOARD_NAND_ADDR_MASK;
        this->IO_ADDR_W &= ~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;
        }
    }


Hardware ECC support
--------------------

Functions and constants
~~~~~~~~~~~~~~~~~~~~~~~

The nand driver supports three different types of hardware ECC.

-  NAND_ECC_HW3_256

   Hardware ECC generator providing 3 bytes ECC per 256 byte.

-  NAND_ECC_HW3_512

   Hardware ECC generator providing 3 bytes ECC per 512 byte.

-  NAND_ECC_HW6_512

   Hardware ECC generator providing 6 bytes ECC per 512 byte.

-  NAND_ECC_HW8_512

   Hardware ECC generator providing 6 bytes ECC per 512 byte.

If your hardware generator has a different functionality add it at the
appropriate place in nand_base.c

The board driver must provide following functions:

-  enable_hwecc

   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.

-  calculate_ecc

   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.

-  correct_data

   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.

Hardware ECC with syndrome calculation
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

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.

The ECC bytes must be placed immediately after the data bytes in order
to make the syndrome generator work. This is contrary to the usual
layout used by software ECC. The separation 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 interfering
with the bad block marker positions. See bad block table support for
details.

Bad block table support
-----------------------

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.

The nand driver supports various types of bad block tables.

-  Per device

   The bad block table contains all bad block information of the device
   which can consist of multiple chips.

-  Per chip

   A bad block table is used per chip and contains the bad block
   information for this particular chip.

-  Fixed offset

   The bad block table is located at a fixed offset in the chip
   (device). This applies to various DiskOnChip devices.

-  Automatic placed

   The bad block table is automatically placed and detected either at
   the end or at the beginning of a chip (device)

-  Mirrored tables

   The bad block table is mirrored on the chip (device) to allow updates
   of the bad block table without data loss.

nand_scan() calls the function nand_default_bbt().
nand_default_bbt() selects appropriate default bad block table
descriptors depending on the chip information which was retrieved by
nand_scan().

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.

Flash based tables
~~~~~~~~~~~~~~~~~~

It may be desired or necessary 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. Therefore 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.

The blocks in which the tables are stored are protected against
accidental access by marking them bad in the memory bad block table. The
bad block table management functions are allowed to circumvent this
protection.

The simplest way to activate the FLASH based bad block table support is
to set the option NAND_BBT_USE_FLASH in the bbt_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

-  Store bad block table per chip

-  Use 2 bits per block

-  Automatic placement at the end of the chip

-  Use mirrored tables with version numbers

-  Reserve 4 blocks at the end of the chip

User defined tables
~~~~~~~~~~~~~~~~~~~

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 necessary 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.

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 rawnand.h to define the options.

-  Number of bits per block

   The supported number of bits is 1, 2, 4, 8.

-  Table per chip

   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.

-  Table location is absolute

   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

-  Table location is automatically detected

   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 structure.
   For mirrored bad block tables different patterns are mandatory.

-  Table creation

   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.

-  Table write support

   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.

   Note: Write support should only be enabled for mirrored tables with
   version control.

-  Table version control

   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 losing 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.

-  Save block contents on write

   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.

-  Number of reserved blocks

   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 bad 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.

Spare area (auto)placement
--------------------------

The nand driver implements different possibilities for placement of
filesystem data in the spare area,

-  Placement defined by fs driver

-  Automatic placement

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.

File system drivers can provide a own placement scheme which is used
instead of the default placement scheme.

Placement schemes are defined by a nand_oobinfo structure

::

    struct nand_oobinfo {
        int useecc;
        int eccbytes;
        int eccpos[24];
        int oobfree[8][2];
    };


-  useecc

   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.

-  eccbytes

   The eccbytes member defines the number of ecc bytes per page.

-  eccpos

   The eccpos array holds the byte offsets in the spare area where the
   ecc codes are placed.

-  oobfree

   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.

Placement defined by fs driver
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

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::

	<spare data page 0><ecc result 0>...<ecc result n>

	...

	<spare data page n><ecc result 0>...<ecc result n>

This is a legacy mode used by YAFFS1.

If the spare area buffer is NULL then only the ECC placement is done
according to the given scheme in the nand_oobinfo structure.

Automatic placement
~~~~~~~~~~~~~~~~~~~

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.

If the spare area buffer is NULL then only the ECC placement is done
according to the default builtin scheme.

Spare area autoplacement default schemes
----------------------------------------

256 byte pagesize
~~~~~~~~~~~~~~~~~

======== ================== ===================================================
Offset   Content            Comment
======== ================== ===================================================
0x00     ECC byte 0         Error correction code byte 0
0x01     ECC byte 1         Error correction code byte 1
0x02     ECC byte 2         Error correction code byte 2
0x03     Autoplace 0
0x04     Autoplace 1
0x05     Bad block marker   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
0x06     Autoplace 2
0x07     Autoplace 3
======== ================== ===================================================

512 byte pagesize
~~~~~~~~~~~~~~~~~


============= ================== ==============================================
Offset        Content            Comment
============= ================== ==============================================
0x00          ECC byte 0         Error correction code byte 0 of the lower
				 256 Byte data in this page
0x01          ECC byte 1         Error correction code byte 1 of the lower
				 256 Bytes of data in this page
0x02          ECC byte 2         Error correction code byte 2 of the lower
				 256 Bytes of data in this page
0x03          ECC byte 3         Error correction code byte 0 of the upper
				 256 Bytes of data in this page
0x04          reserved           reserved
0x05          Bad block marker   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
0x06          ECC byte 4         Error correction code byte 1 of the upper
				 256 Bytes of data in this page
0x07          ECC byte 5         Error correction code byte 2 of the upper
				 256 Bytes of data in this page
0x08 - 0x0F   Autoplace 0 - 7
============= ================== ==============================================

2048 byte pagesize
~~~~~~~~~~~~~~~~~~

=========== ================== ================================================
Offset      Content            Comment
=========== ================== ================================================
0x00        Bad block marker   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
0x01        Reserved           Reserved
0x02-0x27   Autoplace 0 - 37
0x28        ECC byte 0         Error correction code byte 0 of the first
			       256 Byte data in this page
0x29        ECC byte 1         Error correction code byte 1 of the first
			       256 Bytes of data in this page
0x2A        ECC byte 2         Error correction code byte 2 of the first
			       256 Bytes data in this page
0x2B        ECC byte 3         Error correction code byte 0 of the second
			       256 Bytes of data in this page
0x2C        ECC byte 4         Error correction code byte 1 of the second
			       256 Bytes of data in this page
0x2D        ECC byte 5         Error correction code byte 2 of the second
			       256 Bytes of data in this page
0x2E        ECC byte 6         Error correction code byte 0 of the third
			       256 Bytes of data in this page
0x2F        ECC byte 7         Error correction code byte 1 of the third
			       256 Bytes of data in this page
0x30        ECC byte 8         Error correction code byte 2 of the third
			       256 Bytes of data in this page
0x31        ECC byte 9         Error correction code byte 0 of the fourth
			       256 Bytes of data in this page
0x32        ECC byte 10        Error correction code byte 1 of the fourth
			       256 Bytes of data in this page
0x33        ECC byte 11        Error correction code byte 2 of the fourth
			       256 Bytes of data in this page
0x34        ECC byte 12        Error correction code byte 0 of the fifth
			       256 Bytes of data in this page
0x35        ECC byte 13        Error correction code byte 1 of the fifth
			       256 Bytes of data in this page
0x36        ECC byte 14        Error correction code byte 2 of the fifth
			       256 Bytes of data in this page
0x37        ECC byte 15        Error correction code byte 0 of the sixth
			       256 Bytes of data in this page
0x38        ECC byte 16        Error correction code byte 1 of the sixth
			       256 Bytes of data in this page
0x39        ECC byte 17        Error correction code byte 2 of the sixth
			       256 Bytes of data in this page
0x3A        ECC byte 18        Error correction code byte 0 of the seventh
			       256 Bytes of data in this page
0x3B        ECC byte 19        Error correction code byte 1 of the seventh
			       256 Bytes of data in this page
0x3C        ECC byte 20        Error correction code byte 2 of the seventh
			       256 Bytes of data in this page
0x3D        ECC byte 21        Error correction code byte 0 of the eighth
			       256 Bytes of data in this page
0x3E        ECC byte 22        Error correction code byte 1 of the eighth
			       256 Bytes of data in this page
0x3F        ECC byte 23        Error correction code byte 2 of the eighth
			       256 Bytes of data in this page
=========== ================== ================================================

Filesystem support
==================

The NAND driver provides all necessary functions for a filesystem via
the MTD interface.

Filesystems must be aware of the NAND peculiarities 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.

Therefore 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.

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.

Tools
=====

The MTD project provides a couple of helpful tools to handle NAND Flash.

-  flasherase, flasheraseall: Erase and format FLASH partitions

-  nandwrite: write filesystem images to NAND FLASH

-  nanddump: dump the contents of a NAND FLASH partitions

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.

Constants
=========

This chapter describes the constants which might be relevant for a
driver developer.

Chip option constants
---------------------

Constants for chip id table
~~~~~~~~~~~~~~~~~~~~~~~~~~~

These constants are defined in rawnand.h. They are OR-ed together to
describe the chip functionality::

    /* 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


Constants for runtime options
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

These constants are defined in rawnand.h. They are OR-ed together to
describe the functionality::

    /* 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


ECC selection constants
-----------------------

Use these constants to select the ECC algorithm::

    /* 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


Hardware control related constants
----------------------------------

These constants describe the requested hardware access function when the
boardspecific hardware control function is called::

    /* 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


Bad block table related constants
---------------------------------

These constants describe the options used for bad block table
descriptors::

    /* 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
    /* 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
    /* Write bbt if necessary */
    #define NAND_BBT_WRITE      0x00001000
    /* Read and write back block contents when writing bbt */
    #define NAND_BBT_SAVECONTENT    0x00002000


Structures
==========

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.

.. kernel-doc:: include/linux/mtd/rawnand.h
   :internal:

Public Functions Provided
=========================

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.

.. kernel-doc:: drivers/mtd/nand/nand_base.c
   :export:

.. kernel-doc:: drivers/mtd/nand/nand_ecc.c
   :export:

Internal Functions Provided
===========================

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.

.. kernel-doc:: drivers/mtd/nand/nand_base.c
   :internal:

.. kernel-doc:: drivers/mtd/nand/nand_bbt.c
   :internal:

Credits
=======

The following people have contributed to the NAND driver:

1. Steven J. Hill\ sjhill@realitydiluted.com

2. David Woodhouse\ dwmw2@infradead.org

3. Thomas Gleixner\ tglx@linutronix.de

A lot of users have provided bugfixes, improvements and helping hands
for testing. Thanks a lot.

The following people have contributed to this document:

1. Thomas Gleixner\ tglx@linutronix.de