Documentation/mmc/mmc-dev-attrs.txt

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