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

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Message-ID: <2bf37a35-1ccf-f4fa-c999-42b9154a2914@nokia.com>
Date:   Tue, 23 Nov 2021 08:45:49 +0100
From:   Alexander Sverdlin <alexander.sverdlin@...ia.com>
To:     Michael Walle <michael@...le.cc>
Cc:     linux-mtd@...ts.infradead.org,
        Tudor Ambarus <tudor.ambarus@...rochip.com>,
        Pratyush Yadav <p.yadav@...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!

On 22/11/2021 16:05, Michael Walle wrote:
>>>> Ignore 6th ID byte, secure version of mt25qu256a has 0x73 as 6th byte.

...

> Thanks, so that's the SFDP data for the mt25qu256aba8e12-1sit part. and the
> jedec id is 20bb19104473, correct?

Yes!

> You don't have the non-security part by chance?

Unfortunately no. And this is exactly the trigger for this patch:
one can get "secure" parts from Micron even though these "features" are not
required.

> Mh, I'm undecided whether we should just duplicate the entry or if we
> should ignore the last byte ("Device configuration information", where 00h
> is standard). The commit which introduced the flash was 7f412111e276b.
> Vingesh?

Some people ask themselves why this table keeps growing if there is SFDP...
I see the point in fixups, but maybe at some point we will be able to support
some devices just out of the box?

> Can you elaborate on the 0x73? Is that a bitmask? If it was an enumeration,
> I'd assumed it would be 01h (or some smaller value).

This "security addendum" where one need NDA just says "73h = Secure".
There is no explanation for it and no other variants.

I'd really suggest to try to autodetect whatever features are going to be
supported from this chip and only duplicate the entry if this auto-detection
fails.

-- 
Best regards,
Alexander Sverdlin.