Re: [PATCH] mmc: sdio: fix alignment issue in struct sdio_func

Heiner Kallweit
2017-03-29T20:40:18Z

Am 29.03.2017 um 22:17 schrieb Kevin Hilman:
> Heiner Kallweit <hkallweit1@gmail.com> writes:
>
>> Certain 64-bit systems (e.g. Amlogic Meson GX) require buffers to be
>> used for DMA to be 8-byte-aligned. struct sdio_func has an embedded
>> small DMA buffer not meeting this requirement.
>> When testing switching to descriptor chain mode in meson-gx driver
>> SDIO is broken therefore. Fix this by allocating the small DMA buffer
>> separately as kmalloc ensures that the returned memory area is
>> properly aligned for every basic data type.
>>
>> Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
>> Tested-by: Helmut Klein <hgkr.klein@gmail.com>
>
> This should work too, without the need to do a tiny kmalloc.
>
> diff --git a/include/linux/mmc/sdio_func.h b/include/linux/mmc/sdio_func.h
> index aab032a6ae61..071addf23931 100644
> --- a/include/linux/mmc/sdio_func.h
> +++ b/include/linux/mmc/sdio_func.h
> @@ -53,7 +53,7 @@ struct sdio_func {
> unsigned int state; /* function state */
> #define SDIO_STATE_PRESENT (1<<0) /* present in sysfs */
>
> - u8 tmpbuf[4]; /* DMA:able scratch buffer */
> + u8 tmpbuf[4] __aligned(8); /* DMA:able scratch buffer */
>
Yes, that's possible too. Actually I wasn't 100% sure whether the alignment
is applied to each member of the array or the array itself. But after a small
test it seems to be applied to the array.

So let's go with this version, thanks for the hint.

Heiner

> unsigned num_info; /* number of info strings */
> const char **info; /* info strings */
>
> Kevin
>