Re: PXA27x SD/MMC card CRC errors - only sometimes

Richard Purdie wrote:
> On Sat, 2005-12-17 at 13:12 -0700, Matthew Mastracci wrote:
>
> > I tried clocking it down below 19.5MHz (to avoid the PXA27x errata that 
> > indicates that some cards might be a problem at that speed), but that 
> > didn't seem to have any effect.
>
> I have no answer but there are other people seeing issues. There was
> mention of this on linus-arm-kernel:
>
> http://lists.arm.linux.org.uk/pipermail/linux-arm-kernel/2005-December/032798.html
>
> In the followup, I suggested trying lowering the clock speed which
> helped but didn't cure the problem.
>
> It looks like there are some bugs somewhere, perhaps in the timeout
> handling of the pxa driver although there may be more than one issue
> here.

It turns out that this 2GB SD card has a block_size of 10 bits (1024) 
and some part of the block read function is incorrectly setting one of 
the registers.

When I hardcoded the device's blocksize to 9 bits, everything started 
working as expected (though this is obviously not the correct fix):

static void mmc_decode_csd(struct mmc_card *card)
...
+       csd->capacity <<= (csd->read_blkbits - 9);
+       csd->read_blkbits = 9;

I think the problem is basically that mmc_block seems tailored towards 
512-byte sector cards, even though it seems to use csd->read_blkbits in 
a number of places.

Should the mmc layer just always use a 512 byte sector?  This would 
certainly solve this problem.

Matt.