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

[Christophe Leroy]

Le 10/11/2025 à 14:07, Sverdlin, Alexander a écrit :
> 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"?

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?

ack

> > 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@?

Nowadays Fixes: tag seems to be enough to get a fix automagically 
applied to stable branches, but I added it anyway.

> > Closes: https://eur01.safelinks.protection.outlook.com/?url=https%3A%2F%2Flore.kernel.org%2Fall%2F638496dd-ec60-4e53-bad7-eb657f67d580%40csgroup.eu%2F&data=05%7C02%7Cchristophe.leroy%40csgroup.eu%7C5ac2e78d2c44433141df08de205a1e5a%7C8b87af7d86474dc78df45f69a2011bb5%7C0%7C0%7C638983768580305289%7CUnknown%7CTWFpbGZsb3d8eyJFbXB0eU1hcGkiOnRydWUsIlYiOiIwLjAuMDAwMCIsIlAiOiJXaW4zMiIsIkFOIjoiTWFpbCIsIldUIjoyfQ%3D%3D%7C0%7C%7C%7C&sdata=juGQhU%2F%2Fp52t9hPZ5PA0Ka8Ng3ITKNoF%2Bf1%2FP93IkOw%3D&reserved=0
> > Signed-off-by: Christophe Leroy <christophe.leroy@xxxxxxxxxx>
> > ---
> >   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) && "...

Done.

> >   				t->bits_per_word = 16;
> >   		}
> >   	}
>
> You can add my RB tag into your v2.

Thanks
Christophe