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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 raw_rpmb_size_mult RPMB partition size
29 rel_sectors Reliable write sector count
30
31Note on Erase Size and Preferred Erase Size:
32
33 "erase_size" is the minimum size, in bytes, of an erase
34 operation. For MMC, "erase_size" is the erase group size
35 reported by the card. Note that "erase_size" does not apply
36 to trim or secure trim operations where the minimum size is
37 always one 512 byte sector. For SD, "erase_size" is 512
38 if the card is block-addressed, 0 otherwise.
39
40 SD/MMC cards can erase an arbitrarily large area up to and
41 including the whole card. When erasing a large area it may
42 be desirable to do it in smaller chunks for three reasons:
43 1. A single erase command will make all other I/O on
44 the card wait. This is not a problem if the whole card
45 is being erased, but erasing one partition will make
46 I/O for another partition on the same card wait for the
47 duration of the erase - which could be a several
48 minutes.
49 2. To be able to inform the user of erase progress.
50 3. The erase timeout becomes too large to be very
51 useful. Because the erase timeout contains a margin
52 which is multiplied by the size of the erase area,
53 the value can end up being several minutes for large
54 areas.
55
56 "erase_size" is not the most efficient unit to erase
57 (especially for SD where it is just one sector),
58 hence "preferred_erase_size" provides a good chunk
59 size for erasing large areas.
60
61 For MMC, "preferred_erase_size" is the high-capacity
62 erase size if a card specifies one, otherwise it is
63 based on the capacity of the card.
64
65 For SD, "preferred_erase_size" is the allocation unit
66 size specified by the card.
67
68 "preferred_erase_size" is in bytes.
69
70Note on raw_rpmb_size_mult:
71 "raw_rpmb_size_mult" is a mutliple of 128kB block.
72 RPMB size in byte is calculated by using the following equation:
73 RPMB partition size = 128kB x raw_rpmb_size_mult
74
75SD/MMC/SDIO Clock Gating Attribute
76==================================
77
78Read and write access is provided to following attribute.
79This attribute appears only if CONFIG_MMC_CLKGATE is enabled.
80
81 clkgate_delay Tune the clock gating delay with desired value in milliseconds.
82
83echo <desired delay> > /sys/class/mmc_host/mmcX/clkgate_delay