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

[Jun Nie <jun.nie@linaro.org>]

2017-06-13 17:18 GMT+08:00 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.

  Maybe you are right. I had have concern that if preceding member of ECSDData,
CSDData, is not 8 bytes aligned in the tail, UINT8 RESERVED_1[] may start from
non 8 bytes aligned address.

>
>> 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.

512 bytes ECSD data may be read either by CPU or DMA via dedicated
 eMMC command. DMA may require alignment for the structure and
DMA on different SoC may require different alignment. Hikey DMA is
OK with 4 bytes alignment, while ZTE SoC require 8 bytes alignment.
And pad must not be added in the 512 bytes structure body by compiler.
So all members in ECSD are defined as UINT8 is safe.

>
>> 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?

Adding alignment attribute in definition is best way for the constraint, but I
 do not know how to make all compilers happy, just like my version 1 patch.
It is more or less obscure to change VENDOR_SPECIFIC_FIELD or RESERVED_1
to type UINT64.

I confess that adding a pad before ECSD usage is compromised method. It
serve as a reminder for developers too, and allow all members of ECSD are
defined with UINT8.

Another method is to define ECSDData as a pointer and allocate buffer for it.
Which method do you prefer?

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

DWMMC controller on ZTE/Sanchip SoC will read corrupted data with current
DwMmc driver in edk2 96boards git repo. I just add several small patches to
enable it on new SoC. I will send all these changes in near future. Or
what detail
information do you need? I can share it here.

Jun

>
> /
>     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
>> >>