linux-kernel - Re: [PATCH v2 2/2] mtd: spinand: micron: fixing the offset for OOB

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Message-ID: <20230823133956.0a505a20@xps-13>
Date:   Wed, 23 Aug 2023 13:39:56 +0200
From:   Miquel Raynal <miquel.raynal@...tlin.com>
To:     Martin Kurbanov <mmkurbanov@...rdevices.ru>
Cc:     Richard Weinberger <richard@....at>,
        Vignesh Raghavendra <vigneshr@...com>,
        <linux-kernel@...r.kernel.org>, <linux-mtd@...ts.infradead.org>,
        <kernel@...rdevices.ru>
Subject: Re: [PATCH v2 2/2] mtd: spinand: micron: fixing the offset for OOB

Hi Martin,

mmkurbanov@...rdevices.ru wrote on Wed, 23 Aug 2023 14:33:57 +0300:

> Hi Miquel,
> 
> On 23.08.2023 11:41, Miquel Raynal wrote:
> > Hi Martin,
> >
> > I don't think the four bytes have any "bad block specific" meaning. In
> > practice, the datasheet states:
> > 
> > 	Value programmed for bad block at the first byte of spare
> > 	area: 00h
> > 
> > So only the first byte is used to mark the block bad, the rest is
> > probably marked "reserved" for simplicity. I believe we should keep the
> > current layout because it would otherwise break users for no real
> > reason.  
> 
> I agree with you that this can break the work of users who use OOB.
> However, I believe it would be more appropriate to use an offset of 4,
> as the micron chip can use all 4 bytes for additional data about the
> bad block. So, there is a non-zero probability of losing OOB data in
> the reserved area (2 bytes) when the hardware chip attempts to mark
> the block as bad.

Is this really a process the chip can do? Aren't bad blocks factory
marked only?

Then it's mtd's duty to manage them.

Thanks,
Miquèl