1SD and MMC Block Device Attributes
2==================================
3
4These attributes are defined for the block devices associated with the
5SD or MMC device.
6
7The following attributes are read/write.
8
9	force_ro		Enforce read-only access even if write protect switch is off.
10
11SD and MMC Device Attributes
12============================
13
14All attributes are read-only.
15
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	serial			Product Serial Number (from CID Register)
26	erase_size		Erase group size
27	preferred_erase_size	Preferred erase size
28
29Note on Erase Size and Preferred Erase Size:
30
31	"erase_size" is the  minimum size, in bytes, of an erase
32	operation.  For MMC, "erase_size" is the erase group size
33	reported by the card.  Note that "erase_size" does not apply
34	to trim or secure trim operations where the minimum size is
35	always one 512 byte sector.  For SD, "erase_size" is 512
36	if the card is block-addressed, 0 otherwise.
37
38	SD/MMC cards can erase an arbitrarily large area up to and
39	including the whole card.  When erasing a large area it may
40	be desirable to do it in smaller chunks for three reasons:
41		1. A single erase command will make all other I/O on
42		the card wait.  This is not a problem if the whole card
43		is being erased, but erasing one partition will make
44		I/O for another partition on the same card wait for the
45		duration of the erase - which could be a several
46		minutes.
47		2. To be able to inform the user of erase progress.
48		3. The erase timeout becomes too large to be very
49		useful.  Because the erase timeout contains a margin
50		which is multiplied by the size of the erase area,
51		the value can end up being several minutes for large
52		areas.
53
54	"erase_size" is not the most efficient unit to erase
55	(especially for SD where it is just one sector),
56	hence "preferred_erase_size" provides a good chunk
57	size for erasing large areas.
58
59	For MMC, "preferred_erase_size" is the high-capacity
60	erase size if a card specifies one, otherwise it is
61	based on the capacity of the card.
62
63	For SD, "preferred_erase_size" is the allocation unit
64	size specified by the card.
65
66	"preferred_erase_size" is in bytes.
67
68SD/MMC/SDIO Clock Gating Attribute
69==================================
70
71Read and write access is provided to following attribute.
72This attribute appears only if CONFIG_MMC_CLKGATE is enabled.
73
74	clkgate_delay	Tune the clock gating delay with desired value in milliseconds.
75
76echo <desired delay> > /sys/class/mmc_host/mmcX/clkgate_delay
77