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Diffstat (limited to 'Documentation/mmc/mmc-dev-attrs.txt')
| -rw-r--r-- | Documentation/mmc/mmc-dev-attrs.txt | 56 |
1 files changed, 56 insertions, 0 deletions
diff --git a/Documentation/mmc/mmc-dev-attrs.txt b/Documentation/mmc/mmc-dev-attrs.txt new file mode 100644 index 000000000000..ff2bd685bced --- /dev/null +++ b/Documentation/mmc/mmc-dev-attrs.txt @@ -0,0 +1,56 @@ +SD and MMC Device Attributes +============================ + +All attributes are read-only. + + cid Card Identifaction Register + csd Card Specific Data Register + scr SD Card Configuration Register (SD only) + date Manufacturing Date (from CID Register) + fwrev Firmware/Product Revision (from CID Register) (SD and MMCv1 only) + hwrev Hardware/Product Revision (from CID Register) (SD and MMCv1 only) + manfid Manufacturer ID (from CID Register) + name Product Name (from CID Register) + oemid OEM/Application ID (from CID Register) + serial Product Serial Number (from CID Register) + erase_size Erase group size + preferred_erase_size Preferred erase size + +Note on Erase Size and Preferred Erase Size: + + "erase_size" is the minimum size, in bytes, of an erase + operation. For MMC, "erase_size" is the erase group size + reported by the card. Note that "erase_size" does not apply + to trim or secure trim operations where the minimum size is + always one 512 byte sector. For SD, "erase_size" is 512 + if the card is block-addressed, 0 otherwise. + + SD/MMC cards can erase an arbitrarily large area up to and + including the whole card. When erasing a large area it may + be desirable to do it in smaller chunks for three reasons: + 1. A single erase command will make all other I/O on + the card wait. This is not a problem if the whole card + is being erased, but erasing one partition will make + I/O for another partition on the same card wait for the + duration of the erase - which could be a several + minutes. + 2. To be able to inform the user of erase progress. + 3. The erase timeout becomes too large to be very + useful. Because the erase timeout contains a margin + which is multiplied by the size of the erase area, + the value can end up being several minutes for large + areas. + + "erase_size" is not the most efficient unit to erase + (especially for SD where it is just one sector), + hence "preferred_erase_size" provides a good chunk + size for erasing large areas. + + For MMC, "preferred_erase_size" is the high-capacity + erase size if a card specifies one, otherwise it is + based on the capacity of the card. + + For SD, "preferred_erase_size" is the allocation unit + size specified by the card. + + "preferred_erase_size" is in bytes. |