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