diff options
Diffstat (limited to '')
| -rw-r--r-- | Documentation/driver-api/mtdnand.rst | 1006 |
1 files changed, 1006 insertions, 0 deletions
diff --git a/Documentation/driver-api/mtdnand.rst b/Documentation/driver-api/mtdnand.rst new file mode 100644 index 000000000..ce77e024c --- /dev/null +++ b/Documentation/driver-api/mtdnand.rst @@ -0,0 +1,1006 @@ +===================================== +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->legacy.IO_ADDR_W |= CLE_ADRR_BIT; break; + case NAND_CTL_CLRCLE: this->legacy.IO_ADDR_W &= ~CLE_ADRR_BIT; break; + case NAND_CTL_SETALE: this->legacy.IO_ADDR_W |= ALE_ADRR_BIT; break; + case NAND_CTL_CLRALE: this->legacy.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->legacy.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->legacy.IO_ADDR_R = baseaddr; + this->legacy.IO_ADDR_W = baseaddr; + /* Reference hardware control function */ + this->hwcontrol = board_hwcontrol; + /* Set command delay time, see datasheet for correct value */ + this->legacy.chip_delay = CHIP_DEPENDEND_COMMAND_DELAY; + /* Assign the device ready function, if available */ + this->legacy.dev_ready = board_dev_ready; + this->eccmode = NAND_ECC_SOFT; + + /* Scan to find existence of the device */ + if (nand_scan (this, 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) + { + /* Unregister device */ + WARN_ON(mtd_device_unregister(board_mtd)); + /* Release resources */ + nand_cleanup(mtd_to_nand(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->legacy.IO_ADDR_R &= ~BOARD_NAND_ADDR_MASK; + this->legacy.IO_ADDR_W &= ~BOARD_NAND_ADDR_MASK; + switch (chip) { + case 0: + this->legacy.IO_ADDR_R |= BOARD_NAND_ADDR_CHIP0; + this->legacy.IO_ADDR_W |= BOARD_NAND_ADDR_CHIP0; + break; + .... + case n: + this->legacy.IO_ADDR_R |= BOARD_NAND_ADDR_CHIPn; + this->legacy.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 8 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 8 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/raw/nand_base.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/raw/nand_base.c + :internal: + +.. kernel-doc:: drivers/mtd/nand/raw/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 |