[RFC PATCH v5 0/6] refactoring, fixes and updates for Meson NAND

[Arseniy Krasnov]

Hello,

this patchset does several things:

1) Fixes value of ready/busy command. This new value was suggested by
   Liang Yang <liang.yang@xxxxxxxxxxx>.

2) Adds waiting for command completion by calling 'nand_soft_waitrdy()'
   instead of using ready/busy pin and command from 1). This is really
   needed because I don't have device with such pin implemented.

3) It moves OOB free bytes to non-protected by ECC area. Here are some
   details:

   Current OOB free bytes are 4 bytes (2 x 2 user bytes) under ECC engine.
   Here is how it looks like in the current implementation:

   [ 2B user bytes ][     14B ECC codes    ]
   [ 2B user bytes ][     14B ECC codes    ]
   [ 16B unused area, not protected by ECC ]
   [ 16B unused area, not protected by ECC ]

   All 4 user bytes are protected by ECC. This patch changes OOB free
   bytes in this way:

   [ 2B unused area ][     14B ECC codes     ]
   [ 2B unused area ][     14B ECC codes     ]
   [  16B user bytes, not protected by ECC   ]
   [  16B user bytes, not protected by ECC   ]

   Now OOB user bytes are 32 bytes instead of 4 bytes and not protected
   by ECC.

   Motivation of this layout comes from problem with JFFS2. It uses OOB
   free bytes for cleanmarkers. Each cleanmarker is 4 bytes and written
   by JFFS2 driver (small remark - cleanmarkers are always written in
   case of NAND storage for JFFS2).
   We have two ways to write this data to OOB (e.g. user bytes):

   1) ECC mode. In this case it will be ECC covered user bytes, e.g.
      writing this bytes will update ECC codes. Problem fires, when
      JFFS2 tries to write this page later - this write makes controller
      to update ECC codes again, but it is impossible to do it correctly,
      because we can't update bits from 0 to 1 (only from 1 to 0).

   2) Raw mode. In this case ECC codes won't be updated. But later, it
      will be impossible to read this page in ECC mode, because we have
      some user bytes, but ECC codes are missed.

   So let's move OOB free bytes out of ECC area. In this case we can
   read/write OOB separately in raw mode and at the same time work with
   data in ECC mode. JFFS2 is happy now. User bytes are untouched - all
   of them are ignored during non-OOB access.

   I've tested this with mount/unmount/read/write cases for JFFS2 and
   nanddump/nandwrite utlities on AXG family (A113X SoC).

   Here is link to discussion:
   https://lore.kernel.org/linux-mtd/a9f8307a-77d7-a69f-ce11-2629909172d2@xxxxxxxxxxxxxx/T/#m3087bd06386a7f430cd5e343e22b25d724d3e2d7

4) Replaces calculation of OOB related thing with macros. This is just
   cosmetic change.

5) Checks buffer length on accesses to NAND controller.

6) Removes useless bitwise OR with zeroes.

Link to v1:
https://lore.kernel.org/linux-mtd/20230412061700.1492474-1-AVKrasnov@xxxxxxxxxxxxxx/
Link to v2:
https://lore.kernel.org/linux-mtd/20230426073632.3905682-1-AVKrasnov@xxxxxxxxxxxxxx/
Link to v3:
https://lore.kernel.org/linux-mtd/20230510110835.26115-1-AVKrasnov@xxxxxxxxxxxxxx/
Link to v4:
https://lore.kernel.org/linux-mtd/20230515094440.3552094-1-AVKrasnov@xxxxxxxxxxxxxx/

Changelog:

v1 -> v2:
 * Add patch which renames dts value for chip select.
 * Add patch which moves OOB to non-protected ECC area.
v2 -> v3:
 * Change patch which fixes read/write access according discussion link
   in 1) above.
v3 -> v4:
 * Remove patch which renames dts value for chip select.
   Here is link to discussion:
   https://lore.kernel.org/linux-mtd/20230510110835.26115-7-AVKrasnov@xxxxxxxxxxxxxx/
 * Pass 1 to 'meson_nfc_queue_rb()' in case of NAND_OP_WAITRDY_INSTR.
   This fixes ONFI page processing during NAND driver initialization.
v4 -> v5:
 * Move update of 'NFC_CMD_RB_INT' to the separate patch.
 * Replace code which uses extra status and READ0 commands for waiting
   command with 'nand_soft_waitrdy()'. In fact this patch adds second
   mode for command waiting by using 'nand_soft_waitrdy()'.
 * For OOB layout patch see changelog in a patch file.
 * For check length patch see changelog in a patch file.

Arseniy Krasnov (6):
  mtd: rawnand: meson: fix ready/busy command
  mtd: rawnand: meson: wait for command in polling mode
  mtd: rawnand: meson: only expose unprotected user OOB bytes
  mtd: rawnand: meson: use macro for OOB area
  mtd: rawnand: meson: check buffer length
  mtd: rawnand: meson: remove unneeded bitwise OR with zeroes

 drivers/mtd/nand/raw/meson_nand.c | 234 +++++++++++++++++++++++-------
 1 file changed, 182 insertions(+), 52 deletions(-)

-- 
2.35.0