Re: [PATCH] spi: fsl-cpm: Check length parity before switching to 16 bit mode

["Sverdlin, Alexander" <alexander.sverdlin@siemens.com>]

Hi Christophe,

just a couple of nitpicks below:

On Sun, 2025-11-09 at 19:55 +0100, Christophe Leroy wrote:
> Commit fc96ec826bce ("spi: fsl-cpm: Use 16 bit mode for large transfers
> with even size") failed to checkout that the size is really even before
                             ^^^^^^^^
check/verify/"make sure"?

> switching to 16 bit mode. Until recently the problem went unnoticed
> because kernfs uses a pre-allocated bounce buffer of size PAGE_SIZE for
> reading eeprom.
          ^^^^^^
EEPROM?

> But commit 8ad6249c51d0 ("eeprom: at25: convert to spi-mem API")
> introduced an additional dynamically allocated bounce buffer whose size
> is exactly the size of the transfer, leading to a buffer overrun in
> the fsl-cpm driver when that size is odd.
> 
> Add the missing length parity verification and remain in 8 bit mode
> when the length is not even.
> 
> Fixes: fc96ec826bce ("spi: fsl-cpm: Use 16 bit mode for large transfers with even size")

Missing Cc: stable@?

> Closes: https://lore.kernel.org/all/638496dd-ec60-4e53-bad7-eb657f67d580@csgroup.eu/
> Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
> ---
>  drivers/spi/spi-fsl-spi.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/spi/spi-fsl-spi.c b/drivers/spi/spi-fsl-spi.c
> index 2f2082652a1a2..e845baa56cc66 100644
> --- a/drivers/spi/spi-fsl-spi.c
> +++ b/drivers/spi/spi-fsl-spi.c
> @@ -335,7 +335,7 @@ static int fsl_spi_prepare_message(struct spi_controller *ctlr,
>  			if (t->bits_per_word == 16 || t->bits_per_word == 32)
>  				t->bits_per_word = 8; /* pretend its 8 bits */
>  			if (t->bits_per_word == 8 && t->len >= 256 &&
> -			    (mpc8xxx_spi->flags & SPI_CPM1))
> +			    ((t->len & 1) == 0) && (mpc8xxx_spi->flags & SPI_CPM1))

could be written as "!(t->len & 1) && "...

>  				t->bits_per_word = 16;
>  		}
>  	}

You can add my RB tag into your v2.

-- 
Alexander Sverdlin
Siemens AG
www.siemens.com