| SD and MMC Block Device Attributes |
| ================================== |
| |
| These attributes are defined for the block devices associated with the |
| SD or MMC device. |
| |
| The following attributes are read/write. |
| |
| force_ro Enforce read-only access even if write protect switch is off. |
| |
| 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. |
| |
| SD/MMC/SDIO Clock Gating Attribute |
| ================================== |
| |
| Read and write access is provided to following attribute. |
| This attribute appears only if CONFIG_MMC_CLKGATE is enabled. |
| |
| clkgate_delay Tune the clock gating delay with desired value in milliseconds. |
| |
| echo <desired delay> > /sys/class/mmc_host/mmcX/clkgate_delay |
