Re: [PATCH 0/3] mtd: gpmi: add subpage read support

[Huang Shijie <b32955@freescale.com>]

On Fri, Jan 03, 2014 at 11:01:39AM +0800, Huang Shijie wrote:
> 1) Why add the subpage read support?
>   The page size of the nand chip becomes larger and larger, the imx6 has to
>   supports the 16K page or even bigger page. But sometimes, the upper layer only
>   needs a small part of the page, such as 512 bytes or less.
> 
>   For example, ubiattach may only read 64 bytes per page.
> 
> 2) We only enable the subpage read support when it meets the conditions:
>    <1> the chip is imx6 (or later chips) which can supports large nand page.
>    <2> the size of ECC parity is byte aligned.
>        If the size of ECC parity is not byte aligned, the calling of NAND_CMD_RNDOUT
>        will fail.
> 
> 3) What does this patch set do?
>    patch 1: add a new argument for read_subpage hook
>    patch 2: do not use the mtd->writesize. 
>    patch 3: This patch will fake a virtual small page for the subpage read,
>             and call the gpmi_ecc_read_page() to do the real work.
>             In order to fake a virtual small page, the patch changes
> 	    the BCH registers and the bch_geometry{}. After the subpage read
> 	    finished, we will restore them back.
> 
> 4) Performace:
>     4.1) Tested with Toshiba TC58NVG2S0F(4096 + 224) with the following command:
>          #ubiattach /dev/ubi_ctrl -m 4
> 
>        The detail information of /dev/mtd4 shows below:
>        --------------------------------------------------------------
>        #mtdinfo /dev/mtd4
>         mtd4
>         Name:                           test
>         Type:                           nand
>         Eraseblock size:                262144 bytes, 256.0 KiB
>         Amount of eraseblocks:          1856 (486539264 bytes, 464.0 MiB)
>         Minimum input/output unit size: 4096 bytes
>         Sub-page size:                  4096 bytes
>         OOB size:                       224 bytes
>         Character device major/minor:   90:8
>         Bad blocks are allowed:         true
>         Device is writable:             true
>        --------------------------------------------------------------
> 
>     4.2) Before this patch:
>        --------------------------------------------------------------
>        [   94.530495] UBI: attaching mtd4 to ubi0
>        [   98.928850] UBI: scanning is finished
>        [   98.953594] UBI: attached mtd4 (name "test", size 464 MiB) to ubi0
>        [   98.958562] UBI: PEB size: 262144 bytes (256 KiB), LEB size: 253952 bytes
>        [   98.964076] UBI: min./max. I/O unit sizes: 4096/4096, sub-page size 4096
>        [   98.969518] UBI: VID header offset: 4096 (aligned 4096), data offset: 8192
>        [   98.975128] UBI: good PEBs: 1856, bad PEBs: 0, corrupted PEBs: 0
>        [   98.979843] UBI: user volume: 1, internal volumes: 1, max. volumes count: 128
>        [   98.985878] UBI: max/mean erase counter: 2/1, WL threshold: 4096, image sequence number: 2024916145
>        [   98.993635] UBI: available PEBs: 0, total reserved PEBs: 1856, PEBs reserved for bad PEB handling: 40
>        [   99.001807] UBI: background thread "ubi_bgt0d" started, PID 831
>        --------------------------------------------------------------
>        The attach time is about 98.9 - 94.5 = 4.4s
> 
>     4.3) After this patch:
>        --------------------------------------------------------------
>        [  286.464906] UBI: attaching mtd4 to ubi0
>        [  289.186129] UBI: scanning is finished
>        [  289.211416] UBI: attached mtd4 (name "test", size 464 MiB) to ubi0
>        [  289.216360] UBI: PEB size: 262144 bytes (256 KiB), LEB size: 253952 bytes
>        [  289.221858] UBI: min./max. I/O unit sizes: 4096/4096, sub-page size 4096
>        [  289.227293] UBI: VID header offset: 4096 (aligned 4096), data offset: 8192
>        [  289.232878] UBI: good PEBs: 1856, bad PEBs: 0, corrupted PEBs: 0
>        [  289.237628] UBI: user volume: 0, internal volumes: 1, max. volumes count: 128
>        [  289.243553] UBI: max/mean erase counter: 1/1, WL threshold: 4096, image sequence number: 2024916145
>        [  289.251348] UBI: available PEBs: 1812, total reserved PEBs: 44, PEBs reserved for bad PEB handling: 40
>        [  289.259417] UBI: background thread "ubi_bgt0d" started, PID 847
>        --------------------------------------------------------------
>        The attach time is about 289.18 - 286.46 = 2.7s
> 
>      4.4) The conclusion:
>        We achieve (4.4 - 2.7) / 4.4 = 38.6% faster in the ubiattach.
> 
>  5) This patch depends on the following patch:
>     http://lists.infradead.org/pipermail/linux-mtd/2013-December/051091.html
> 
> Huang Shijie (3):
>   mtd: nand: add "page" argument for read_subpage hook
>   mtd: gpmi: do not use the mtd->writesize
>   mtd: gpmi: add subpage read support
> 
>  drivers/mtd/nand/gpmi-nand/gpmi-nand.c |  102 +++++++++++++++++++++++++++++++-
>  drivers/mtd/nand/nand_base.c           |    7 ++-
>  include/linux/mtd/nand.h               |    2 +-
>  3 files changed, 105 insertions(+), 6 deletions(-)
> 
> -- 
> 1.7.2.rc3
> 
> 
just a ping.

Best Regards
Huang Shijie