On Mon, 14 Sep 2009 20:34:35 +0530
"Ghorai, Sukumar" <s-ghorai@xxxxxx> wrote:
> Hello,
>
> I am working in Linux MMC driver.
> Recently I came across one 16GB MMC card where EXT_CSD Register having EXT_CSD_REV[192] field as ZERO, which is valid according to Specification. But card is not working due to following reason -
>
> 1. As we know there are two fields in Extended CSD Register - CSD_STRUCTURE Version[194] & EXT_CSD_REV Revision [192].
>
>
> 1. In mmc.c/ mmc_read_ext_csd ()
> * Implementation expecting EXT_CSD_REV non zero (e.g. >3 in current code)
> * I think it could be checking for CSD_STRUCTURE version.
> * Because EXT_CSD_REV having Zero is the valid Field.
> * This is the way it's done in other OS too.
The opposite, it expects the version to be below 3 as those are the
only ones it knows about. Checking the CSD version for the EXT_CSD
would just be silly.
>
>
> 1. To check the high capacity card.
> * We could check in access mode from OCR. This is not in Linux exactly and steps to check the EXT_CSD_REV.
> * This is done in some other OS too.
>
Checking the OCR is insufficient if I remember the spec correctly, so
we ignore it completely. The EXT_CSD needs to be correct for high
capacity to work anyway.
> So do you think we can update the code to check the CSD_STRUCTURE Version? Please let us know your opinion.
No, as that would violate the spec and possibly misinterpret some cards
as high-capacity.
To handle your card you would have to build some kind of quirks system
so that the kernel can identify that this card is buggy and compensate
for it.
Rgds
--
-- Pierre Ossman
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