Documentation/mmc/mmc-dev-attrs.txt

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.

	num_wr_reqs_to_start_packing 	This attribute is used to determine
	the trigger for activating the write packing, in case the write
	packing control feature is enabled.

	When the MMC manages to reach a point where num_wr_reqs_to_start_packing
	write requests could be packed, it enables the write packing feature.
	This allows us to start the write packing only when it is beneficial
	and has minimum affect on the read latency.

	The number of potential packed requests that will trigger the packing
	can be configured via sysfs by writing the required value to:
	/sys/block/<block_dev_name>/num_wr_reqs_to_start_packing.

	The default value of num_wr_reqs_to_start_packing was determined by
	running parallel lmdd write and lmdd read operations and calculating
	the max number of packed writes requests.

	min_sectors_to_check_bkops_status	This attribute is used to
	determine whether the status bit that indicates the need for BKOPS
	should be checked. The value is stored in this attribute represents
	the minimum number of sectors that needs to be changed in the device
	(written or discarded) in order to require the status-bit of BKOPS
	to be checked. The value can modified via sysfs by writing the
	required value to:
	/sys/block/<block_dev_name>/min_sectors_to_check_bkops_status

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

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.

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