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

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

2017-06-13 12:25 GMT+08:00 Andrew Fish <afish@apple.com>:
>
> On Jun 12, 2017, at 9:13 PM, Jun Nie <jun.nie@linaro.org> wrote:
>
> 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?
>
>
> Sure
>
> type struct {
>   UINT16 RCA;
>   UINT8   CardType;
>   UINT32 OCRData;
> ...
>
> Has different alignment than:
> type struct {
>   UINT16 RCA;
>   UINT32 CardType;
>   UINT32 OCRData;
> ...
>
> Both are legal things for the C compiler to due given the type is an enum.
> 1st example OCRData starts at offset 4
> 2nd example OCRData starts at offset 8
>
> An integer type is not an int.
>
> Thanks,
>
> Andrew Fish

But I do not care about OCRData. I just care the alignment of
ECSDData, which is the last member and I assume it shall be impacted
just by the previous member alignment. Does ECSDData alignment cannot
be secured with Pad change if enum is the 2nd member? If so, is it
safe if I make sure the first member in ECSDData is UINT64?

 typedef struct  {
  UINT16 RCA;
  UINT8   CardType;
  OCR       OCRData;
  CID       CIDData;
  CSD       CSDData;
+  UINT64    Pad;                              // For 8 bytes
alignment of ECSDData
   ECSD      ECSDData;                         // MMC V4 extended card specific
 } CARD_INFO;

Thanks!
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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