linux-kernel - Re: [PATCH] mtd: spi-nor: mt25qu: Ignore 6th ID byte

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Message-ID: <8742b6e8-c26e-47d7-0b77-67137d3de10f@nokia.com>
Date:   Thu, 25 Nov 2021 08:26:59 +0100
From:   Alexander Sverdlin <alexander.sverdlin@...ia.com>
To:     Pratyush Yadav <p.yadav@...com>
Cc:     Michael Walle <michael@...le.cc>, linux-mtd@...ts.infradead.org,
        Tudor Ambarus <tudor.ambarus@...rochip.com>,
        Miquel Raynal <miquel.raynal@...tlin.com>,
        Richard Weinberger <richard@....at>,
        Vignesh Raghavendra <vigneshr@...com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mtd: spi-nor: mt25qu: Ignore 6th ID byte

Hi Pratyush,

thanks for the quick reply!

On 23/11/2021 18:42, Pratyush Yadav wrote:
>> In my opinion, as I look into Micron or Macronix datasheets, write_proto has little to
>> do with erase_proto. (there is currently no separate erase_proto)
> I think this just worked for most flashes since both writes and erases 
> generally use 1-bit mode. 4 or 8 bit modes are generally used for reads 
> only.
> 
>> Before I come up with a totally wrong patch, wanted to ask your opinion, how should
>> it be solved, what do you think?
>>
>> I do not see any erase-related tables for this in JESD216C.
>> I also cannot come up with an example of a chip with erase != 1-1-0.
> See Micron MT35XU512ABA or Cypress S28HS512T (in spansion.c). Both have 
> erase in 8D-8D-8D mode.
> 
>> Shall I hardcode 1-1-0 for erase?
>> Shall I introduce erase_proto? What would be the logic for its setting/discovery?
> I think introducing erase_proto would be the sensible thing. You would 
> have to see if we can discover erase protocol from SFDP. But my question 
> is: is that really worth it? Do you really need that little bit speed 
> boost you'd get by transmitting write data in 4 bit mode, since the 
> large portion of the time would be spent in the chip actually flashing 
> the data.

The problem I have is not speed, but totally not working erase. And I don't want
to downgrade write functionality for other chips.

-- 
Best regards,
Alexander Sverdlin.