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 Identification 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) prv Product Revision (from CID Register) (SD and MMCv4 only) 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 ocr Operation Conditions Register dsr Driver Stage Register cmdq_en
Command Queue enabled:1 => enabled, 0 => not enabled
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:
- 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.
- To be able to inform the user of erase progress.
- 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 multiple of 128kB block.
RPMB size in byte is calculated by using the following equation:RPMB partition size = 128kB x raw_rpmb_size_mult