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

[Andrew Fish <afish@apple.com>]

> On Jun 12, 2017, at 7:14 PM, Jun Nie <jun.nie@linaro.org> 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?
>> 
>> /
>>    Leif
> 
> 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. Changing the
> first member to "UINT64 RESERVED_1[2]" shall secure the alignment. But
> I preferred Pad method. It is more readable if all ECSD member are
> UINT8 type. It is also more clear to add alignment info in CARD_INFO,
> just before ECSD member.
> I do not get point of Andrew, maybe he share the same concern.
> 

Jun

typedef enum {
  UNKNOWN_CARD,
  MMC_CARD,              //MMC card
  MMC_CARD_HIGH,         //MMC Card with High capacity
  EMMC_CARD,             //eMMC 4.41 card
  SD_CARD,               //SD 1.1 card
  SD_CARD_2,             //SD 2.0 or above standard card
  SD_CARD_2_HIGH         //SD 2.0 or above high capacity card
} CARD_TYPE;

Per C spec sizeof(CARD_TYPE) can be 1, 2, 4, or 8 (64-bit integer), and it is legal for the compiler to pick any of these. So it is not portable C code to use an enum in a data structure when layout maters.

Thanks,

Andrew Fish


> 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
>>> 
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