RE: [PATCH v2] mmc: core: Verify SD bus width

From: Avri Altman
Date: Thu Apr 18 2019 - 02:20:32 EST

> The SD Physical Layer Spec says the following: Since the SD Memory Card
> shall support at least the two bus modes 1-bit or 4-bit width, then any SD
> Card shall set at least bits 0 and 2 (SD_BUS_WIDTH="0101").
> This change verifies the card has specified a bus width.
> AMD SDHC Device 7806 can get into a bad state after a card disconnect
> where anything transferred via the DATA lines will always result in a
> zero filled buffer. Currently the driver will continue without error if
> the HC is in this condition. A block device will be created, but reading
> from it will result in a zero buffer. This makes it seem like the SD
> device has been erased, when in actuality the data is never getting
> copied from the DATA lines to the data buffer.
> SCR is the first command in the SD initialization sequence that uses the
> DATA lines. By checking that the response was invalid, we can abort
> mounting the card.
> Acked-by: Avri Altman <avri.altman@xxxxxxx>
> Signed-off-by: Raul E Rangel <rrangel@xxxxxxxxxxxx>
Reviewed-by: Avri Altman <avri.altman@xxxxxxx>