diff options
Diffstat (limited to '')
| -rw-r--r-- | Documentation/mtd/nand/pxa3xx-nand.txt | 113 |
1 files changed, 0 insertions, 113 deletions
diff --git a/Documentation/mtd/nand/pxa3xx-nand.txt b/Documentation/mtd/nand/pxa3xx-nand.txt deleted file mode 100644 index 1074cbc67ec6..000000000000 --- a/Documentation/mtd/nand/pxa3xx-nand.txt +++ /dev/null @@ -1,113 +0,0 @@ - -About this document -=================== - -Some notes about Marvell's NAND controller available in PXA and Armada 370/XP -SoC (aka NFCv1 and NFCv2), with an emphasis on the latter. - -NFCv2 controller background -=========================== - -The controller has a 2176 bytes FIFO buffer. Therefore, in order to support -larger pages, I/O operations on 4 KiB and 8 KiB pages is done with a set of -chunked transfers. - -For instance, if we choose a 2048 data chunk and set "BCH" ECC (see below) -we'll have this layout in the pages: - - ------------------------------------------------------------------------------ - | 2048B data | 32B spare | 30B ECC || 2048B data | 32B spare | 30B ECC | ... | - ------------------------------------------------------------------------------ - -The driver reads the data and spare portions independently and builds an internal -buffer with this layout (in the 4 KiB page case): - - ------------------------------------------ - | 4096B data | 64B spare | - ------------------------------------------ - -Also, for the READOOB command the driver disables the ECC and reads a 'spare + ECC' -OOB, one per chunk read. - - ------------------------------------------------------------------- - | 4096B data | 32B spare | 30B ECC | 32B spare | 30B ECC | - ------------------------------------------------------------------- - -So, in order to achieve reading (for instance), we issue several READ0 commands -(with some additional controller-specific magic) and read two chunks of 2080B -(2048 data + 32 spare) each. -The driver accommodates this data to expose the NAND core a contiguous buffer -(4096 data + spare) or (4096 + spare + ECC + spare + ECC). - -ECC -=== - -The controller has built-in hardware ECC capabilities. In addition it is -configurable between two modes: 1) Hamming, 2) BCH. - -Note that the actual BCH mode: BCH-4 or BCH-8 will depend on the way -the controller is configured to transfer the data. - -In the BCH mode the ECC code will be calculated for each transferred chunk -and expected to be located (when reading/programming) right after the spare -bytes as the figure above shows. - -So, repeating the above scheme, a 2048B data chunk will be followed by 32B -spare, and then the ECC controller will read/write the ECC code (30B in -this case): - - ------------------------------------ - | 2048B data | 32B spare | 30B ECC | - ------------------------------------ - -If the ECC mode is 'BCH' then the ECC is *always* 30 bytes long. -If the ECC mode is 'Hamming' the ECC is 6 bytes long, for each 512B block. -So in Hamming mode, a 2048B page will have a 24B ECC. - -Despite all of the above, the controller requires the driver to only read or -write in multiples of 8-bytes, because the data buffer is 64-bits. - -OOB -=== - -Because of the above scheme, and because the "spare" OOB is really located in -the middle of a page, spare OOB cannot be read or write independently of the -data area. In other words, in order to read the OOB (aka READOOB), the entire -page (aka READ0) has to be read. - -In the same sense, in order to write to the spare OOB the driver has to write -an *entire* page. - -Factory bad blocks handling -=========================== - -Given the ECC BCH requires to layout the device's pages in a split -data/OOB/data/OOB way, the controller has a view of the flash page that's -different from the specified (aka the manufacturer's) view. In other words, - -Factory view: - - ----------------------------------------------- - | Data |x OOB | - ----------------------------------------------- - -Driver's view: - - ----------------------------------------------- - | Data | OOB | Data x | OOB | - ----------------------------------------------- - -It can be seen from the above, that the factory bad block marker must be -searched within the 'data' region, and not in the usual OOB region. - -In addition, this means under regular usage the driver will write such -position (since it belongs to the data region) and every used block is -likely to be marked as bad. - -For this reason, marking the block as bad in the OOB is explicitly -disabled by using the NAND_BBT_NO_OOB_BBM option in the driver. The rationale -for this is that there's no point in marking a block as bad, because good -blocks are also 'marked as bad' (in the OOB BBM sense) under normal usage. - -Instead, the driver relies on the bad block table alone, and should only perform -the bad block scan on the very first time (when the device hasn't been used). |