[PATCH RFC] MMC card of Size > 4GB support in Linu

Pierre Ossman pierre at ossman.eu
Wed Sep 23 02:06:52 EDT 2009

On Sat, 19 Sep 2009 17:52:23 +0530
"Ghorai, Sukumar" <s-ghorai at ti.com> wrote:

> IV). And what I understood from MMCA specification is that - 
> EXT_CSD[EXT_CSD_REV]: Defines the fixed parameters and related to the EXT_CSD register, according to its revision. And it's nothing to do with MMCA specification version or to support > 4GB card.
> V). But in current Linux MMC code it's expecting EXT_CSD_REV should be >=2; 
> And if any card of size >= 4GB and EXT_CSD_REV field value is <2, 
> And MMC card won't work.
> I have seen cards which having EXT_CSD_REV is <2 and working in other OS.
> So, Here I am sending the possible solution. `

We've been over this already. Your card is broken. Making the stack
misbehave for not only your card, but every card, is not a good

The SEC_COUNT field wasn't added until MMC v4.2, and they changed the
EXT_CSD_REV to 1.2 to indicate this new format. You're suggesting that
we ignore the revision field and just read undefined bits, hoping that
they are meaningful. Nobody can consider that a reliable system.

> diff --git a/include/linux/mmc/mmc.h b/include/linux/mmc/mmc.h
> index 14b81f3..c4e97a9 100644
> --- a/include/linux/mmc/mmc.h
> +++ b/include/linux/mmc/mmc.h
> @@ -252,6 +252,7 @@ struct _mmc_csd {
>  #define EXT_CSD_BUS_WIDTH      183     /* R/W */
>  #define EXT_CSD_HS_TIMING      185     /* R/W */
>  #define EXT_CSD_CARD_TYPE      196     /* RO */
> +#define EXT_CSD_STRUCT_REV 194     /* RO */
>  #define EXT_CSD_REV            192     /* RO */
>  #define EXT_CSD_SEC_CNT                212     /* RO, 4 bytes */

And this is just even more wrong. You're telling the stack to check the
revision of the CSD, a completely different structure, for what fields
are valid in the EXT_CSD.

     -- Pierre Ossman

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