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Documentation / mmc / mmc-dev-attrs.txt




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Based on kernel version 3.13. Page generated on 2014-01-20 22:03 EST.

1	SD and MMC Block Device Attributes
2	==================================
3	
4	These attributes are defined for the block devices associated with the
5	SD or MMC device.
6	
7	The following attributes are read/write.
8	
9		force_ro		Enforce read-only access even if write protect switch is off.
10	
11	SD and MMC Device Attributes
12	============================
13	
14	All 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		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
31	
32	Note on Erase Size and Preferred Erase Size:
33	
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.
40	
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.
56	
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.
61	
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.
65	
66		For SD, "preferred_erase_size" is the allocation unit
67		size specified by the card.
68	
69		"preferred_erase_size" is in bytes.
70	
71	Note 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
75	
76	SD/MMC/SDIO Clock Gating Attribute
77	==================================
78	
79	Read and write access is provided to following attribute.
80	This attribute appears only if CONFIG_MMC_CLKGATE is enabled.
81	
82		clkgate_delay	Tune the clock gating delay with desired value in milliseconds.
83	
84	echo <desired delay> > /sys/class/mmc_host/mmcX/clkgate_delay
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