linux/Documentation/mmc/mmc-dev-attrs.txt
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   1SD and MMC Block Device Attributes
   2==================================
   3
   4These attributes are defined for the block devices associated with the
   5SD or MMC device.
   6
   7The following attributes are read/write.
   8
   9        force_ro                Enforce read-only access even if write protect switch is off.
  10
  11SD and MMC Device Attributes
  12============================
  13
  14All attributes are read-only.
  15
  16        cid                     Card Identifaction Register
  17        csd                     Card Specific Data Register
  18        scr                     SD Card Configuration Register (SD only)
  19        date                    Manufacturing Date (from CID Register)
  20        fwrev                   Firmware/Product Revision (from CID Register) (SD and MMCv1 only)
  21        hwrev                   Hardware/Product Revision (from CID Register) (SD and MMCv1 only)
  22        manfid                  Manufacturer ID (from CID Register)
  23        name                    Product Name (from CID Register)
  24        oemid                   OEM/Application ID (from CID Register)
  25        prv                     Product Revision (from CID Register) (SD and MMCv4 only)
  26        serial                  Product Serial Number (from CID Register)
  27        erase_size              Erase group size
  28        preferred_erase_size    Preferred erase size
  29        raw_rpmb_size_mult      RPMB partition size
  30        rel_sectors             Reliable write sector count
  31
  32Note on Erase Size and Preferred Erase Size:
  33
  34        "erase_size" is the  minimum size, in bytes, of an erase
  35        operation.  For MMC, "erase_size" is the erase group size
  36        reported by the card.  Note that "erase_size" does not apply
  37        to trim or secure trim operations where the minimum size is
  38        always one 512 byte sector.  For SD, "erase_size" is 512
  39        if the card is block-addressed, 0 otherwise.
  40
  41        SD/MMC cards can erase an arbitrarily large area up to and
  42        including the whole card.  When erasing a large area it may
  43        be desirable to do it in smaller chunks for three reasons:
  44                1. A single erase command will make all other I/O on
  45                the card wait.  This is not a problem if the whole card
  46                is being erased, but erasing one partition will make
  47                I/O for another partition on the same card wait for the
  48                duration of the erase - which could be a several
  49                minutes.
  50                2. To be able to inform the user of erase progress.
  51                3. The erase timeout becomes too large to be very
  52                useful.  Because the erase timeout contains a margin
  53                which is multiplied by the size of the erase area,
  54                the value can end up being several minutes for large
  55                areas.
  56
  57        "erase_size" is not the most efficient unit to erase
  58        (especially for SD where it is just one sector),
  59        hence "preferred_erase_size" provides a good chunk
  60        size for erasing large areas.
  61
  62        For MMC, "preferred_erase_size" is the high-capacity
  63        erase size if a card specifies one, otherwise it is
  64        based on the capacity of the card.
  65
  66        For SD, "preferred_erase_size" is the allocation unit
  67        size specified by the card.
  68
  69        "preferred_erase_size" is in bytes.
  70
  71Note on raw_rpmb_size_mult:
  72        "raw_rpmb_size_mult" is a mutliple of 128kB block.
  73        RPMB size in byte is calculated by using the following equation:
  74        RPMB partition size = 128kB x raw_rpmb_size_mult
  75
  76SD/MMC/SDIO Clock Gating Attribute
  77==================================
  78
  79Read and write access is provided to following attribute.
  80This attribute appears only if CONFIG_MMC_CLKGATE is enabled.
  81
  82        clkgate_delay   Tune the clock gating delay with desired value in milliseconds.
  83
  84echo <desired delay> > /sys/class/mmc_host/mmcX/clkgate_delay
  85
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