linux-kernel - Re: [RESEND PATCH 1/2] mtd: spi-nor: do not touch TB bit without SPI_NOR_HAS

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Message-ID: <758b2772-3c44-1184-066e-df890d05a21a@ti.com>
Date:   Wed, 30 Sep 2020 19:30:28 +0530
From:   Vignesh Raghavendra <vigneshr@...com>
To:     Ivan Mikhaylov <i.mikhaylov@...ro.com>,
        Tudor Ambarus <tudor.ambarus@...rochip.com>,
        Miquel Raynal <miquel.raynal@...tlin.com>,
        Richard Weinberger <richard@....at>
CC:     <linux-mtd@...ts.infradead.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [RESEND PATCH 1/2] mtd: spi-nor: do not touch TB bit without
 SPI_NOR_HAS_TB



On 9/30/20 6:37 PM, Ivan Mikhaylov wrote:
> On Wed, 2020-09-30 at 15:06 +0530, Vignesh Raghavendra wrote:
>>
>> On 9/21/20 4:54 PM, Ivan Mikhaylov wrote:
>>> Some chips like macronix don't have TB(Top/Bottom protection)
>>> bit in the status register. Do not write tb_mask inside status
>>> register, unless SPI_NOR_HAS_TB is present for the chip.
>>>
>>
>> Not entirely accurate.. Macronix chips have TB bit in config register
>> and is OTP and hence should not be touched ideally...
>>
>> You still need to "read" that bit to determine actual scheme (Top vs
>> Bottom). This is needs to be done before 2/2 enables SPI_NOR_HAS_LOCK
>> flag for macronix flashes.
> 
> Vignesh, that's the point about this commit to generalize this part about TB bit
> plus there is already exist SPI_NOR_HAS_TB flag which representing state of TB
> existence. I didn't add any support for macronix's TB bit, that's true but
> that's enough to make macronix chips able to use lock mechanism with default
> 'use_top' or any other chips which doesn't have TB bit.

Right, but 2/2 "enables" locking mechanism for Macronix flashes. Therefore its 
necessary to take TB bit into account so that implementation is correct. 
What if OTP bit is set as "use_bottom"? Although this is non default, 
we need to take care of this case for correctness.

> 
>> I guess macronix does not support SR_SRWD right? This needs special
>> treatment as well.
> 
> It does support SR_SRWD as well. No need any special treatment here.
> 

I did not find it in one Macronix datasheet at least:
https://www.macronix.com/Lists/Datasheet/Attachments/7902/MX25L25673G,%203V,%20256Mb,%20v1.6.pdf

Are you sure all Macronix flashes support SRWD?

> Thanks.
>