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

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

2017-06-13 12:01 GMT+08:00 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

CARD_TYPE CardType is 2nd member of CARD_INFO, while ECSDData is the
last member and I just want to align it to 8 bytes. I had assume pad
will be added automatically by compiler if CARD_TYPE is not 8 bytes
aligned and UNIT64 type appear in following member. Does enum will
impact the later member alignment? Could you help elaborate more about
this?

Thank you!
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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>