Documentation/driver-api/mmc/mmc-dev-attrs.rst

   1 ==================================
   2 SD and MMC Block Device Attributes
   3 ==================================
   4
   5 These attributes are defined for the block devices associated with the
   6 SD or MMC device.
   7
   8 The following attributes are read/write.
   9
  10         ========                ===============================================
  11         force_ro                Enforce read-only access even if write protect                                  switch is off.
  12         ========                ===============================================
  13
  14 SD and MMC Device Attributes
  15 ============================
  16
  17 All attributes are read-only.
  18
  19         ======================  ===============================================
  20         cid                     Card Identification Register
  21         csd                     Card Specific Data Register
  22         scr                     SD Card Configuration Register (SD only)
  23         date                    Manufacturing Date (from CID Register)
  24         fwrev                   Firmware/Product Revision (from CID Register)
  25                                 (SD and MMCv1 only)
  26         hwrev                   Hardware/Product Revision (from CID Register)
  27                                 (SD and MMCv1 only)
  28         manfid                  Manufacturer ID (from CID Register)
  29         name                    Product Name (from CID Register)
  30         oemid                   OEM/Application ID (from CID Register)
  31         prv                     Product Revision (from CID Register)
  32                                 (SD and MMCv4 only)
  33         serial                  Product Serial Number (from CID Register)
  34         erase_size              Erase group size
  35         preferred_erase_size    Preferred erase size
  36         raw_rpmb_size_mult      RPMB partition size
  37         rel_sectors             Reliable write sector count
  38         ocr                     Operation Conditions Register
  39         dsr                     Driver Stage Register
  40         cmdq_en                 Command Queue enabled:
  41
  42                                         1 => enabled, 0 => not enabled
  43         ======================  ===============================================
  44
  45 Note on Erase Size and Preferred Erase Size:
  46
  47         "erase_size" is the  minimum size, in bytes, of an erase
  48         operation.  For MMC, "erase_size" is the erase group size
  49         reported by the card.  Note that "erase_size" does not apply
  50         to trim or secure trim operations where the minimum size is
  51         always one 512 byte sector.  For SD, "erase_size" is 512
  52         if the card is block-addressed, 0 otherwise.
  53
  54         SD/MMC cards can erase an arbitrarily large area up to and
  55         including the whole card.  When erasing a large area it may
  56         be desirable to do it in smaller chunks for three reasons:
  57
  58              1. A single erase command will make all other I/O on
  59                 the card wait.  This is not a problem if the whole card
  60                 is being erased, but erasing one partition will make
  61                 I/O for another partition on the same card wait for the
  62                 duration of the erase - which could be a several
  63                 minutes.
  64              2. To be able to inform the user of erase progress.
  65              3. The erase timeout becomes too large to be very
  66                 useful.  Because the erase timeout contains a margin
  67                 which is multiplied by the size of the erase area,
  68                 the value can end up being several minutes for large
  69                 areas.
  70
  71         "erase_size" is not the most efficient unit to erase
  72         (especially for SD where it is just one sector),
  73         hence "preferred_erase_size" provides a good chunk
  74         size for erasing large areas.
  75
  76         For MMC, "preferred_erase_size" is the high-capacity
  77         erase size if a card specifies one, otherwise it is
  78         based on the capacity of the card.
  79
  80         For SD, "preferred_erase_size" is the allocation unit
  81         size specified by the card.
  82
  83         "preferred_erase_size" is in bytes.
  84
  85 Note on raw_rpmb_size_mult:
  86
  87         "raw_rpmb_size_mult" is a multiple of 128kB block.
  88
  89         RPMB size in byte is calculated by using the following equation:
  90
  91                 RPMB partition size = 128kB x raw_rpmb_size_mult