Re: [PATCH v2] EmbeddedPkg/MmcDxe: Add alignment for ECSD data

[Leif Lindholm <leif.lindholm@linaro.org>]

On Tue, Jun 13, 2017 at 10:14:34AM +0800, Jun Nie wrote:
> 2017-06-12 23:53 GMT+08:00 Leif Lindholm <leif.lindholm@linaro.org>:
> > On Mon, Jun 12, 2017 at 09:59:28AM +0800, Jun Nie wrote:
> >> Add alignment for ECSD data for DMA access. Otherwise
> >> the data is corrupted on Sanechips platform.
> >
> > I never did see a reply to my proposed solution, and the below is not
> > it. Can you explain why you prefer this one?
> 
> Sorry, just see your email because that thread is not highlighted for
> new email in gmail for unknown reason.
> I have concern that "UINT64 VENDOR_SPECIFIC_FIELD[8]" cannot secure
> the ECSD alignment because it is not the first member.

It being the first member or not has no relevance.
By my count, it starts at offset 64, with all preceding entries being
UINT8.

> Changing the first member to "UINT64 RESERVED_1[2]" shall secure the
> alignment.

Relying on a reserved field for setting alignment constraints risks
having to find an alternative method at some point in the future, so I
agree this is not a preferred solution.

> But I preferred Pad method. It is more readable if all ECSD member
> are UINT8 type.

I confess am not familiar enough with eMMC to make a clean call here,
but if real alignment constrains exist, using UINT8 is actively
misleading, not to mention incorrect. If there is no real alignment
constraint, this is not the code that needs fixing.

> It is also more clear to add alignment info in
> CARD_INFO, just before ECSD member.

Why is it more clear to apply alignment constraints at point of use
instead of point of definition?

Is there any chance you can share the EFI_MMC_HOST_PROTOCOL
implementation that triggers this error?

/
    Leif

> I do not get point of Andrew, maybe he share the same concern.
> 
> Jun
> 
> >
> >> Contributed-under: TianoCore Contribution Agreement 1.0
> >> Signed-off-by: Jun Nie <jun.nie@linaro.org>
> >> ---
> >>  EmbeddedPkg/Universal/MmcDxe/Mmc.h | 1 +
> >>  1 file changed, 1 insertion(+)
> >>
> >> diff --git a/EmbeddedPkg/Universal/MmcDxe/Mmc.h b/EmbeddedPkg/Universal/MmcDxe/Mmc.h
> >> index 8a7d5a3..6e3ab17 100644
> >> --- a/EmbeddedPkg/Universal/MmcDxe/Mmc.h
> >> +++ b/EmbeddedPkg/Universal/MmcDxe/Mmc.h
> >> @@ -319,6 +319,7 @@ typedef struct  {
> >>    OCR       OCRData;
> >>    CID       CIDData;
> >>    CSD       CSDData;
> >> +  UINT64    Pad;                              // For 8 bytes alignment of ECSDData
> >>    ECSD      ECSDData;                         // MMC V4 extended card specific
> >>  } CARD_INFO;
> >>
> >> --
> >> 1.9.1
> >>