xref: /openbmc/linux/Documentation/driver-api/mmc/mmc-dev-attrs.rst (revision 19024c09)

==================================
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 Identification 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
	ocr 			Operation Conditions Register
	dsr			Driver Stage Register
	cmdq_en			Command Queue enabled:

					1 => enabled, 0 => not enabled
	======================	===============================================

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 multiple of 128kB block.

	RPMB size in byte is calculated by using the following equation:

		RPMB partition size = 128kB x raw_rpmb_size_mult