Re: [PATCH] MMC-4.5 Data Tag Support

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On 21 December 2011 16:23, Girish K S <girish.shivananjappa@xxxxxxxxxx> wrote:
> On 21 December 2011 13:09, Saugata Das <saugata.das@xxxxxxxxxxxxxx> wrote:
>> From: Saugata Das <saugata.das@xxxxxxxxxx>
>>
>> MMC-4.5 data tag feature will be used to store the file system meta-data in the
>> tagged region of eMMC. This will improve the write and subsequent read transfer
>> time for the meta data.
>>
>> Signed-off-by: Saugata Das <saugata.das@xxxxxxxxxx>
>> ---
>>  drivers/mmc/card/block.c |   17 +++++++++++++++--
>>  drivers/mmc/core/mmc.c   |   14 ++++++++++++++
>>  include/linux/mmc/card.h |    2 ++
>>  include/linux/mmc/mmc.h  |    3 +++
>>  4 files changed, 34 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/mmc/card/block.c b/drivers/mmc/card/block.c
>> index a1cb21f..af3b6c3 100644
>> --- a/drivers/mmc/card/block.c
>> +++ b/drivers/mmc/card/block.c
>> @@ -995,6 +995,7 @@ static void mmc_blk_rw_rq_prep(struct mmc_queue_req *mqrq,
>>        struct mmc_blk_request *brq = &mqrq->brq;
>>        struct request *req = mqrq->req;
>>        struct mmc_blk_data *md = mq->data;
>> +       bool do_data_tag;
>>
>>        /*
>>         * Reliable writes are used to implement Forced Unit Access and
>> @@ -1071,6 +1072,16 @@ static void mmc_blk_rw_rq_prep(struct mmc_queue_req *mqrq,
>>                mmc_apply_rel_rw(brq, card, req);
>>
>>        /*
>> +        * Data tag is used only during writing meta data to speed
>> +        * up write and any subsequent read of this meta data
>> +        */
>> +       do_data_tag = (card->ext_csd.data_tag_unit_size) &&
>> +               (req->cmd_flags & REQ_META) &&
>> +               (rq_data_dir(req) == WRITE) &&
>> +               ((brq->data.blocks * brq->data.blksz) >=
>> +               card->ext_csd.data_tag_unit_size) ;
>> +
>> +       /*
>>         * Pre-defined multi-block transfers are preferable to
>>         * open ended-ones (and necessary for reliable writes).
>>         * However, it is not sufficient to just send CMD23,
>> @@ -1091,10 +1102,12 @@ static void mmc_blk_rw_rq_prep(struct mmc_queue_req *mqrq,
>>
>>        if ((md->flags & MMC_BLK_CMD23) &&
>>            mmc_op_multi(brq->cmd.opcode) &&
>> -           (do_rel_wr || !(card->quirks & MMC_QUIRK_BLK_NO_CMD23))) {
>> +           (do_rel_wr || !(card->quirks & MMC_QUIRK_BLK_NO_CMD23) ||
>> +               do_data_tag)) {
>>                brq->sbc.opcode = MMC_SET_BLOCK_COUNT;
>>                brq->sbc.arg = brq->data.blocks |
>> -                       (do_rel_wr ? (1 << 31) : 0);
>> +                       (do_rel_wr ? (1 << 31) : 0) |
>> +                       (do_data_tag ? (1 << 29) : 0);
>>                brq->sbc.flags = MMC_RSP_R1 | MMC_CMD_AC;
>>                brq->mrq.sbc = &brq->sbc;
>>        }
>> diff --git a/drivers/mmc/core/mmc.c b/drivers/mmc/core/mmc.c
>> index dbf421a..244049b 100644
>> --- a/drivers/mmc/core/mmc.c
>> +++ b/drivers/mmc/core/mmc.c
>> @@ -488,6 +488,20 @@ static int mmc_read_ext_csd(struct mmc_card *card, u8 *ext_csd)
>>                        ext_csd[EXT_CSD_CACHE_SIZE + 1] << 8 |
>>                        ext_csd[EXT_CSD_CACHE_SIZE + 2] << 16 |
>>                        ext_csd[EXT_CSD_CACHE_SIZE + 3] << 24;
>> +
>> +               if (ext_csd[EXT_CSD_DATA_SECTOR_SIZE] == 1)
>> +                       card->ext_csd.data_sector_size = 4096;
>> +               else
>> +                       card->ext_csd.data_sector_size = 512;
>> +
>> +               if ((ext_csd[EXT_CSD_DATA_TAG_SUPPORT] & 1) &&
>> +                       (ext_csd[EXT_CSD_TAG_UNIT_SIZE] <= 8)) {
>> +                       card->ext_csd.data_tag_unit_size =
>> +                       ((unsigned int) 1 << ext_csd[EXT_CSD_TAG_UNIT_SIZE]) *
>> +                       (card->ext_csd.data_sector_size);
>> +               } else {
>> +                       card->ext_csd.data_tag_unit_size = 0;
>> +               }
>>        }
>>
>>  out:
>> diff --git a/include/linux/mmc/card.h b/include/linux/mmc/card.h
>> index 415f2db..a55668d 100644
>> --- a/include/linux/mmc/card.h
>> +++ b/include/linux/mmc/card.h
>> @@ -71,6 +71,8 @@ struct mmc_ext_csd {
>>        bool                    hpi_en;                 /* HPI enablebit */
>>        bool                    hpi;                    /* HPI support bit */
>>        unsigned int            hpi_cmd;                /* cmd used as HPI */
>> +       unsigned int            data_sector_size;       /* 512Bytes or 4KB */
>> +       unsigned int            data_tag_unit_size;     /* DATA TAG UNIT size */
>>        u8                      raw_partition_support;  /* 160 */
>>        u8                      raw_erased_mem_count;   /* 181 */
>>        u8                      raw_ext_csd_structure;  /* 194 */
>> diff --git a/include/linux/mmc/mmc.h b/include/linux/mmc/mmc.h
>> index 0e71356..e076f7f 100644
>> --- a/include/linux/mmc/mmc.h
>> +++ b/include/linux/mmc/mmc.h
>> @@ -273,6 +273,7 @@ struct _mmc_csd {
>>  #define EXT_CSD_FLUSH_CACHE            32      /* W */
>>  #define EXT_CSD_CACHE_CTRL             33      /* R/W */
>>  #define EXT_CSD_POWER_OFF_NOTIFICATION 34      /* R/W */
>> +#define EXT_CSD_DATA_SECTOR_SIZE       61      /* R */
>>  #define EXT_CSD_GP_SIZE_MULT           143     /* R/W */
>>  #define EXT_CSD_PARTITION_ATTRIBUTE    156     /* R/W */
>>  #define EXT_CSD_PARTITION_SUPPORT      160     /* RO */
>> @@ -313,6 +314,8 @@ struct _mmc_csd {
>>  #define EXT_CSD_POWER_OFF_LONG_TIME    247     /* RO */
>>  #define EXT_CSD_GENERIC_CMD6_TIME      248     /* RO */
>>  #define EXT_CSD_CACHE_SIZE             249     /* RO, 4 bytes */
>> +#define EXT_CSD_TAG_UNIT_SIZE          498     /* RO */
>> +#define EXT_CSD_DATA_TAG_SUPPORT       499     /* RO */
>>  #define EXT_CSD_HPI_FEATURES           503     /* RO */
>>
>>  /*
>
> TAG_RES_SIZE in the extended csd register mentions about the resource
> size utilised by the device to keep data tag.
> This can be used to avoid the data exhaustion case.
>

Once the tag resource is exhausted, the further tag data writes will
be ignored by eMMC and those will be written to the non-tagged or
default area of eMMC (ref to section 6.6.25 in 4.5 spec : "The data
shall still be written to the device regardless of the resources
exhaustion; however, it may not have the improved characteristics").
So, host driver need not do additional tracking of the amount of data
written using tag option.


>> --
>> 1.7.4.3
>>
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