linux-kernel - Re: [PATCH 3/4] dt-bindings: mtd: macronix,mx25l12833f: add SPI-NOR chip

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Date: Fri, 28 Jun 2024 19:17:42 +0200
From: Erez <erezgeva2@...il.com>
To: Michael Walle <mwalle@...nel.org>
Cc: Conor Dooley <conor@...nel.org>, Erez Geva <erezgeva@...ime.org>, linux-mtd@...ts.infradead.org, 
	Tudor Ambarus <tudor.ambarus@...aro.org>, Pratyush Yadav <pratyush@...nel.org>, 
	linux-kernel@...r.kernel.org, Miquel Raynal <miquel.raynal@...tlin.com>, 
	Richard Weinberger <richard@....at>, Vignesh Raghavendra <vigneshr@...com>, devicetree@...r.kernel.org, 
	Rob Herring <robh@...nel.org>, Krzysztof Kozlowski <krzk+dt@...nel.org>, Conor Dooley <conor+dt@...nel.org>
Subject: Re: [PATCH 3/4] dt-bindings: mtd: macronix,mx25l12833f: add SPI-NOR chip

On Fri, 28 Jun 2024 at 18:51, Michael Walle <mwalle@...nel.org> wrote:
>
> On Fri Jun 28, 2024 at 6:30 PM CEST, Erez wrote:
> > I do not know why they decided to use the same JEDEC ID for two chips.
> > Your guess is as good as mine.
>
> That's a common pattern and we try hard to figure that out during
> probe time instead of hardcoding it. E.g. by looking at the SFDP
> data. Have a look at various fixups in drivers/mtd/spi-nor/.

That's a good approach.
The obsolete mx25l12805d does not support the SFDP table.
The new mx25l12833f does.

What is the kernel policy regarding obsolete flash chips?
Macronix annonce on end of life of mx25l12805d in 2010.
Perhaps we should remove mx25l12805d,
 and leave the mx25l12833f configuration in mtd/spi-nor/macronix.c?

>
> compatibles are really the last resort to distinguish flash devices.

I totally agree. Use JEDEC ID a lot better.
In this case Macronix decided to reuse an obsolete chip ID.

>
> Next time, please mention such information in the commit message,
> please.

Thanks for the tip.
I did write it in the fourth patch, but I can add it in part 3 as well.

> Also please have a look at
> https://docs.kernel.org/driver-api/mtd/spi-nor.html

The new mx25l12833f supports SFDP, the obsolete mx25l12805d does not.
I did manage to read the SFDP, though I do not have a copy of it (I do
not have the hardware any more).
To my best knowledge SFDP table do not contain information on OTP,

Thanks
  Erez Geva

>
> -michael