linux-kernel - Re: [PATCH 2/5] mtd: rawnand: qcom: remove driver specific block

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Message-ID: <20180720150348.592c8984@bbrezillon>
Date:   Fri, 20 Jul 2018 15:03:48 +0200
From:   Boris Brezillon <boris.brezillon@...tlin.com>
To:     Abhishek Sahu <absahu@...eaurora.org>
Cc:     Miquel Raynal <miquel.raynal@...tlin.com>,
        David Woodhouse <dwmw2@...radead.org>,
        Brian Norris <computersforpeace@...il.com>,
        Marek Vasut <marek.vasut@...il.com>,
        Richard Weinberger <richard@....at>,
        linux-arm-msm@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-mtd@...ts.infradead.org, Andy Gross <andy.gross@...aro.org>
Subject: Re: [PATCH 2/5] mtd: rawnand: qcom: remove driver specific
 block_markbad function

On Fri, 20 Jul 2018 17:46:38 +0530
Abhishek Sahu <absahu@...eaurora.org> wrote:

> Hi Boris,
> 
> On 2018-07-19 03:13, Boris Brezillon wrote:
> > On Wed, 18 Jul 2018 23:23:50 +0200
> > Miquel Raynal <miquel.raynal@...tlin.com> wrote:
> >   
> >> Boris,
> >> 
> >> Can you please check the change in qcom_nandc_write_oob() is
> >> valid? I think it is but as this is a bit of a hack I prefer double 
> >> checking.  
> > 
> > Indeed, it's hack-ish.
> >   
> >> 
> >> Thanks,
> >> Miquèl
> >> 
> >> 
> >> Abhishek Sahu <absahu@...eaurora.org> wrote on Fri,  6 Jul 2018
> >> 13:21:56 +0530:
> >>   
> >> > The NAND base layer calls write_oob() by setting bytes at
> >> > chip->badblockpos with value non 0xFF for updating bad block status.
> >> > The QCOM NAND controller skips the bad block bytes while doing normal
> >> > write with ECC enabled. When initial support for this driver was
> >> > added, the driver specific function was added temporarily for
> >> > block_markbad() with assumption to change for raw read in NAND base
> >> > layer. Moving to raw read for block_markbad() seems to take more time
> >> > so this patch removes driver specific block_markbad() function by
> >> > using following HACK in write_oob() function.
> >> >
> >> > Check for BBM bytes in OOB and accordingly do raw write for updating
> >> > BBM bytes in NAND flash or normal write for updating available OOB
> >> > bytes.  
> > 
> > Why don't we change that instead of patching the qcom driver to guess
> > when the core tries to mark a block bad? If you're afraid of breaking
> > existing drivers that might rely on the "write/read BBM in non-raw
> > mode" solution (I'm sure some drivers are), you can always add a new
> > flag in chip->options (NAND_ACCESS_BBM_IN_RAW_MODE) and only use raw
> > accessors when this flag is set.
> >   
> 
>   We started with that Only
> 
>   http://patchwork.ozlabs.org/patch/508565/
> 
>   and since we didn't conclude, we went for driver
>   specific bad block check and mark bad block functions.
> 
>   Now, we wanted to get rid of driver specific functions
> 
>   1. For bad block check, we found the way to get the BBM bytes
>      with ECC read. Controller updates BBM in separate register
>      which we can read and update the same in OOB. Patch #1 of
>      series does the same.
> 
>   2. For bad block mark, there is no way to update in ECC mode
>      that's why we went for HACK to get rid of driver specific
>      function.
> 
>   If adding flag is fine now then this HACK won't be required.

Yep. I'm fine with that. Can you rebase the patch you pointed out on top
of nand/next and move the flag to chip->options instead of
chip->bbt_options + prefix it with NAND_ instead of NAND_BBT_?


>   Moving to RAW mode for every one still looks risky.

I agree.