Re: [PATCH 1/2] mtd: spi-nor: Fix RDCR controller capability core check

From: Pratyush Yadav <pratyush@kernel.org>
To: Miquel Raynal <miquel.raynal@bootlin.com>
Cc: Richard Weinberger <richard@nod.at>,
	 Vignesh Raghavendra <vigneshr@ti.com>,
	 Tudor Ambarus <tudor.ambarus@linaro.org>,
	 Pratyush Yadav <pratyush@kernel.org>,
	 Michael Walle <michael@walle.cc>,
	<linux-mtd@lists.infradead.org>,
	 Jakub Czapiga <czapiga@google.com>,
	Thomas Petazzoni <thomas.petazzoni@bootlin.com>,
	 Takahiro Kuwano <takahiro.kuwano@infineon.com>
Subject: Re: [PATCH 1/2] mtd: spi-nor: Fix RDCR controller capability core check
Date: Fri, 13 Mar 2026 11:10:50 +0000	[thread overview]
Message-ID: <2vxz4imkf0hx.fsf@kernel.org> (raw)
In-Reply-To: <873429oxwf.fsf@bootlin.com> (Miquel Raynal's message of "Mon, 09 Mar 2026 15:55:28 +0100")

On Mon, Mar 09 2026, Miquel Raynal wrote:

> Hello SPI NOR folks :-)
>
> + Takahiro
>
> On 08/01/2026 at 13:14:29 +01, Miquel Raynal <miquel.raynal@bootlin.com> wrote:
>
>> Commit 5008c3ec3f89 ("mtd: spi-nor: core: Check read CR support") adds a
>> controller check to make sure the core will not use CR reads on
>> controllers not supporting them. The approach is valid but the fix is
>> incorrect. Unfortunately, the author could not catch it, because the
>> expected behavior was met. The patch indeed drops the RDCR capability,
>> but it does it for all controllers!
>>
>> The issue comes from the use of spi_nor_spimem_check_op() which is an
>> internal helper dedicated to check page operations, ie. it is only used
>> for page reads and page programs (despite its generic name).
>>
>> This helper looks for the biggest number of address bytes that can be
>> used for a page operation and tries 4 then 3. It then calls the usual
>> spi-mem helpers to do the checks. These will always fail because there
>> is now an inconsistency: the address cycles are forced to 4 (then 3)
>> bytes, but the bus width during the address cycles rightfully remains 0:
>> impossible, the operation is invalid.
>>
>> The correct check in this case is to directly call spi_mem_supports_op()
>> which doesn't messes up with the operation content.
>>
>> Fixes: 5008c3ec3f89 ("mtd: spi-nor: core: Check read CR support")
>> Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
>
> These two patches are fixes which need to get in, I'd like to pick them
> for the next fixes MTD PR that I am preparing, but I was expecting some
> kind of acknowledgement on it.

With Tudor's suggestions:

Reviewed-by: Pratyush Yadav <pratyush@kernel.org>

I am going through the SPI NOR patch backlog. Since you plan to take
these directly via mtd/fixes, I'll not queue these.

[...]

-- 
Regards,
Pratyush Yadav

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