Initial import

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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)
+	prv			Product Revision (from CID Register) (SD and MMCv4 only)
+	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