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. num_wr_reqs_to_start_packing This attribute is used to determine the trigger for activating the write packing, in case the write packing control feature is enabled. When the MMC manages to reach a point where num_wr_reqs_to_start_packing write requests could be packed, it enables the write packing feature. This allows us to start the write packing only when it is beneficial and has minimum affect on the read latency. The number of potential packed requests that will trigger the packing can be configured via sysfs by writing the required value to: /sys/block//num_wr_reqs_to_start_packing. The default value of num_wr_reqs_to_start_packing was determined by running parallel lmdd write and lmdd read operations and calculating the max number of packed writes requests. 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 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 SD/MMC/SDIO Clock Scaling Attributes ==================================== Read and write accesses are provided to following attributes. polling_interval Measured in milliseconds, this attribute defines how often we need to check the card usage and make decisions on frequency scaling. up_threshold This attribute defines what should be the average card usage between the polling interval for the mmc core to make a decision on whether it should increase the frequency. For example when it is set to '35' it means that between the checking intervals the card needs to be on average more than 35% in use to scale up the frequency. The value should be between 0 - 100 so that it can be compared against load percentage. down_threshold Similar to up_threshold, but on lowering the frequency. For example, when it is set to '2' it means that between the checking intervals the card needs to be on average less than 2% in use to scale down the clocks to minimum frequency. The value should be between 0 - 100 so that it can be compared against load percentage. enable Enable clock scaling for hosts (and cards) that support ultrahigh speed modes (SDR104, DDR50, HS200). echo > /sys/class/mmc_host/mmcX/clk_scaling/polling_interval echo > /sys/class/mmc_host/mmcX/clk_scaling/up_threshold echo > /sys/class/mmc_host/mmcX/clk_scaling/down_threshold echo > /sys/class/mmc_host/mmcX/clk_scaling/enable