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+SD and MMC Block Device Attributes
+These attributes are defined for the block devices associated with the
+SD or MMC device.
+The following attributes are read/write.
+ force_ro Enforce read-only access even if write protect switch is off.
+SD and MMC Device Attributes
+All attributes are read-only.
+ cid Card Identifaction Register
+ csd Card Specific Data Register
+ scr SD Card Configuration Register (SD only)
+ date Manufacturing Date (from CID Register)
+ fwrev Firmware/Product Revision (from CID Register) (SD and MMCv1 only)
+ hwrev Hardware/Product Revision (from CID Register) (SD and MMCv1 only)
+ manfid Manufacturer ID (from CID Register)
+ name Product Name (from CID Register)
+ oemid OEM/Application ID (from CID Register)
+ serial Product Serial Number (from CID Register)
+ erase_size Erase group size
+ preferred_erase_size Preferred erase size
+ raw_rpmb_size_mult RPMB partition size
+ rel_sectors Reliable write sector count
+Note on Erase Size and Preferred Erase Size:
+ "erase_size" is the minimum size, in bytes, of an erase
+ operation. For MMC, "erase_size" is the erase group size
+ reported by the card. Note that "erase_size" does not apply
+ to trim or secure trim operations where the minimum size is
+ always one 512 byte sector. For SD, "erase_size" is 512
+ if the card is block-addressed, 0 otherwise.
+ SD/MMC cards can erase an arbitrarily large area up to and
+ including the whole card. When erasing a large area it may
+ be desirable to do it in smaller chunks for three reasons:
+ 1. A single erase command will make all other I/O on
+ the card wait. This is not a problem if the whole card
+ is being erased, but erasing one partition will make
+ I/O for another partition on the same card wait for the
+ duration of the erase - which could be a several
+ minutes.
+ 2. To be able to inform the user of erase progress.
+ 3. The erase timeout becomes too large to be very
+ useful. Because the erase timeout contains a margin
+ which is multiplied by the size of the erase area,
+ the value can end up being several minutes for large
+ areas.
+ "erase_size" is not the most efficient unit to erase
+ (especially for SD where it is just one sector),
+ hence "preferred_erase_size" provides a good chunk
+ size for erasing large areas.
+ For MMC, "preferred_erase_size" is the high-capacity
+ erase size if a card specifies one, otherwise it is
+ based on the capacity of the card.
+ For SD, "preferred_erase_size" is the allocation unit
+ size specified by the card.
+ "preferred_erase_size" is in bytes.
+Note on raw_rpmb_size_mult:
+ "raw_rpmb_size_mult" is a mutliple of 128kB block.
+ RPMB size in byte is calculated by using the following equation:
+ RPMB partition size = 128kB x raw_rpmb_size_mult
+SD/MMC/SDIO Clock Gating Attribute
+Read and write access is provided to following attribute.
+This attribute appears only if CONFIG_MMC_CLKGATE is enabled.
+ clkgate_delay Tune the clock gating delay with desired value in milliseconds.
+echo <desired delay> > /sys/class/mmc_host/mmcX/clkgate_delay