1SD and MMC Block Device Attributes
   4These attributes are defined for the block devices associated with the
   5SD or MMC device.
   7The following attributes are read/write.
   9        force_ro                Enforce read-only access even if write protect switch is off.
  11SD and MMC Device Attributes
  14All attributes are read-only.
  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        serial                  Product Serial Number (from CID Register)
  26        erase_size              Erase group size
  27        preferred_erase_size    Preferred erase size
  29Note on Erase Size and Preferred Erase Size:
  31        "erase_size" is the  minimum size, in bytes, of an erase
  32        operation.  For MMC, "erase_size" is the erase group size
  33        reported by the card.  Note that "erase_size" does not apply
  34        to trim or secure trim operations where the minimum size is
  35        always one 512 byte sector.  For SD, "erase_size" is 512
  36        if the card is block-addressed, 0 otherwise.
  38        SD/MMC cards can erase an arbitrarily large area up to and
  39        including the whole card.  When erasing a large area it may
  40        be desirable to do it in smaller chunks for three reasons:
  41                1. A single erase command will make all other I/O on
  42                the card wait.  This is not a problem if the whole card
  43                is being erased, but erasing one partition will make
  44                I/O for another partition on the same card wait for the
  45                duration of the erase - which could be a several
  46                minutes.
  47                2. To be able to inform the user of erase progress.
  48                3. The erase timeout becomes too large to be very
  49                useful.  Because the erase timeout contains a margin
  50                which is multiplied by the size of the erase area,
  51                the value can end up being several minutes for large
  52                areas.
  54        "erase_size" is not the most efficient unit to erase
  55        (especially for SD where it is just one sector),
  56        hence "preferred_erase_size" provides a good chunk
  57        size for erasing large areas.
  59        For MMC, "preferred_erase_size" is the high-capacity
  60        erase size if a card specifies one, otherwise it is
  61        based on the capacity of the card.
  63        For SD, "preferred_erase_size" is the allocation unit
  64        size specified by the card.
  66        "preferred_erase_size" is in bytes.
  68SD/MMC/SDIO Clock Gating Attribute
  71Read and write access is provided to following attribute.
  72This attribute appears only if CONFIG_MMC_CLKGATE is enabled.
  74        clkgate_delay   Tune the clock gating delay with desired value in milliseconds.
  76echo <desired delay> > /sys/class/mmc_host/mmcX/clkgate_delay
  77 kindly hosted by Redpill Linpro AS, provider of Linux consulting and operations services since 1995.