[PATCH] mtd: nand: Disable subpage writes for drivers without ecc->hwctl

[Gupta, Pekon]

>From: Helmut Schaa [mailto:helmut.schaa at googlemail.com]
>>On Wed, Apr 9, 2014 at 11:38 AM, Gupta, Pekon <pekon at ti.com> wrote:
[...]
>>
>> (1) if chip->ecc.hwctl() and chip->ecc.calculate are not implemented but you
>>  still want to use subpage write feature, then you need to provide custom
>>  implementation for chip->ecc.write_subpage().
>>  that's same for other interfaces of nand_chip like chip->ecc.write_page().
>
>But these don't cause panics :)
>
because fsl_elbc_nand.c uses custom implementations of chip->ecc.write_page()
	@@ fsl_elbc_chip_init(...)
		chip->ecc.write_page = fsl_elbc_write_page;

Same needs to be done if subpage write is needed. However, as this is
a regression so please check if following patch solves your problem.[1]


>> (2) If you don't want to use subpage write feature then just disable it using
>>         chip->options |= NAND_NO_SUBPAGE_WRITE;
>>
>> Can you please tell which NAND controller driver is causing this ?
>> We need to fix that..
>
>This happens with fsl_elbc_nand (while trying to run ubiformat on a
>mtd dev) but the
>crash was caused by the introduction of nand_write_subpage_hwecc. So, in this
>case I think instead of trying to fix every possible driver we should
>let the nand core
>code handle this issue gracefully. Maybe we could add a WARN_ON_ONCE to
>notice which drivers require adjustments.
>
Yes agree. May be good to keep subpage write disabled by default,
as only handful drivers possibly use that.


[1] ## <not compile tested>
------------
>From bfd39102ed6aa99b7ac2b8394a2d12b879fbb4b7 Mon Sep 17 00:00:00 2001
From: Pekon Gupta <pekon at ti.com>
Date: Wed, 9 Apr 2014 15:51:25 +0530
Subject: [PATCH] mtd: eLBC NAND: disable subpage write support

As fsl_elbc_nand do not implement NAND ECC interfaces (like chip->ecc.hwctl(),
chip->ecc.calculate, and chip->ecc.correct) So it cannot use default
implementation of nand_write_subpage_hwecc() as in nand_base.c.
Hence disabling subpage write support till a custom implementation for
chip->ecc_write_subpage is added.

CC: <stable at vger.kernel.org> # 3.10.x+
Signed-off-by: Pekon Gupta <pekon at ti.com>
---
 drivers/mtd/nand/fsl_elbc_nand.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/mtd/nand/fsl_elbc_nand.c b/drivers/mtd/nand/fsl_elbc_nand.c
index ec549cd..a21252c 100644
--- a/drivers/mtd/nand/fsl_elbc_nand.c
+++ b/drivers/mtd/nand/fsl_elbc_nand.c
@@ -755,6 +755,7 @@ static int fsl_elbc_chip_init(struct fsl_elbc_mtd *priv)

        /* set up nand options */
        chip->bbt_options = NAND_BBT_USE_FLASH;
+       chip->options |= NAND_NO_SUBPAGE_WRITE;

        chip->controller = &elbc_fcm_ctrl->controller;
        chip->priv = priv;
--
1.8.5.1.163.gd7aced9

----------------
(looping possible maintainers of this driver Huang Shijie and Scott Wood)

with regards, pekon