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

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Date:   Tue, 30 Nov 2021 15:19:58 +0530
From:   Pratyush Yadav <p.yadav@...com>
To:     Alexander Sverdlin <alexander.sverdlin@...ia.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

On 25/11/21 08:26AM, Alexander Sverdlin wrote:
> 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.

Then you need to introduce erase_proto.

-- 
Regards,
Pratyush Yadav
Texas Instruments Inc.