linux-kernel - Re: [PATCH] mtd: dc21285: fix bytewise memcpy()

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Message-Id: <bb5c1c40-874a-4b30-b606-1785f00e9be9@app.fastmail.com>
Date: Thu, 07 Aug 2025 13:55:08 +0200
From: "Arnd Bergmann" <arnd@...db.de>
To: "Miquel Raynal" <miquel.raynal@...tlin.com>,
 "Arnd Bergmann" <arnd@...nel.org>
Cc: "Richard Weinberger" <richard@....at>,
 "Vignesh Raghavendra" <vigneshr@...com>,
 "Nathan Chancellor" <nathan@...nel.org>,
 "David Woodhouse" <dwmw2@...radead.org>,
 "Nick Desaulniers" <nick.desaulniers+lkml@...il.com>,
 "Bill Wendling" <morbo@...gle.com>, "Justin Stitt" <justinstitt@...gle.com>,
 linux-mtd@...ts.infradead.org, linux-kernel@...r.kernel.org,
 llvm@...ts.linux.dev
Subject: Re: [PATCH] mtd: dc21285: fix bytewise memcpy()

On Thu, Aug 7, 2025, at 09:54, Miquel Raynal wrote:
>
> On 07/08/2025 at 09:20:34 +02, Arnd Bergmann <arnd@...nel.org> wrote:
>
>> From: Arnd Bergmann <arnd@...db.de>
>>
>> The commit that split up the 8/16/32-bit operations in 2004 seems to have
>> broken the 8-bit case, as clang-21 now points out:
>>
>> drivers/mtd/maps/dc21285.c:129:97: error: parameter 'len' set but not used [-Werror,-Wunused-but-set-parameter]
>>   129 | static void dc21285_copy_to_8(struct map_info *map, unsigned long to, const void *from, ssize_t len)
>>
>> Put back the loop that was in linux-2.6.8 and earlier for this case.
>>
>> Fixes: 67d4878e4e61 ("NOR flash drivers update")
>> Cc: David Woodhouse <dwmw2@...radead.org>
>> Signed-off-by: Arnd Bergmann <arnd@...db.de>
>
> Thanks for the patch, I'll take it, but that probably means few to no
> people still use it, if broken for more than 20 years...

Yes, certainly. I also have a patch to mark the mach-footbridge
platform as deprecated and schedule it for removal, I need to
resend that patch.

What I suspect happened here is that the bug was harmless
because the few boards that use this driver all have
16-bit or 32-bit flashes, while the 8-bit codepath was indeed
unused.

    Arnd