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Andrei Warkentin371a6892011-04-11 18:10:25 -05001SD 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
Adrian Hunterdfe86cb2010-08-11 14:17:46 -070011SD 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.
Sujit Reddy Thumma597dd9d792011-11-14 13:53:29 +053067
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
Stephen Boyd4137e502011-12-05 10:28:44 -080074 clkgate_delay Tune the clock gating delay with desired value in milliseconds.
Sujit Reddy Thumma597dd9d792011-11-14 13:53:29 +053075
76echo <desired delay> > /sys/class/mmc_host/mmcX/clkgate_delay