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 raw_rpmb_size_mult RPMB partition size rel_sectors Reliable write sector count 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. Note on raw_rpmb_size_mult: "raw_rpmb_size_mult" is a mutliple of 128kB block. RPMB size in byte is calculated by using the following equation: RPMB partition size = 128kB x raw_rpmb_size_mult 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 > /sys/class/mmc_host/mmcX/clkgate_delay