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371a689f AW |
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 | ||
dfe86cba AH |
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 | serial Product Serial Number (from CID Register) | |
26 | erase_size Erase group size | |
27 | preferred_erase_size Preferred erase size | |
28 | ||
29 | Note 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. | |
597dd9d7 SRT |
67 | |
68 | SD/MMC/SDIO Clock Gating Attribute | |
69 | ================================== | |
70 | ||
71 | Read and write access is provided to following attribute. | |
72 | This attribute appears only if CONFIG_MMC_CLKGATE is enabled. | |
73 | ||
4137e504 | 74 | clkgate_delay Tune the clock gating delay with desired value in milliseconds. |
597dd9d7 SRT |
75 | |
76 | echo <desired delay> > /sys/class/mmc_host/mmcX/clkgate_delay |