140 lines
5.4 KiB
Text
140 lines
5.4 KiB
Text
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SD and MMC Block Device Attributes
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==================================
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These attributes are defined for the block devices associated with the
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SD or MMC device.
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The following attributes are read/write.
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force_ro Enforce read-only access even if write protect switch is off.
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num_wr_reqs_to_start_packing This attribute is used to determine
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the trigger for activating the write packing, in case the write
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packing control feature is enabled.
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When the MMC manages to reach a point where num_wr_reqs_to_start_packing
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write requests could be packed, it enables the write packing feature.
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This allows us to start the write packing only when it is beneficial
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and has minimum affect on the read latency.
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The number of potential packed requests that will trigger the packing
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can be configured via sysfs by writing the required value to:
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/sys/block/<block_dev_name>/num_wr_reqs_to_start_packing.
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The default value of num_wr_reqs_to_start_packing was determined by
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running parallel lmdd write and lmdd read operations and calculating
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the max number of packed writes requests.
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SD and MMC Device Attributes
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============================
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All attributes are read-only.
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cid Card Identification Register
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csd Card Specific Data Register
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scr SD Card Configuration Register (SD only)
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date Manufacturing Date (from CID Register)
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fwrev Firmware/Product Revision (from CID Register) (SD and MMCv1 only)
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hwrev Hardware/Product Revision (from CID Register) (SD and MMCv1 only)
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manfid Manufacturer ID (from CID Register)
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name Product Name (from CID Register)
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oemid OEM/Application ID (from CID Register)
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prv Product Revision (from CID Register) (SD and MMCv4 only)
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serial Product Serial Number (from CID Register)
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erase_size Erase group size
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preferred_erase_size Preferred erase size
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raw_rpmb_size_mult RPMB partition size
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rel_sectors Reliable write sector count
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Note on Erase Size and Preferred Erase Size:
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"erase_size" is the minimum size, in bytes, of an erase
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operation. For MMC, "erase_size" is the erase group size
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reported by the card. Note that "erase_size" does not apply
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to trim or secure trim operations where the minimum size is
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always one 512 byte sector. For SD, "erase_size" is 512
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if the card is block-addressed, 0 otherwise.
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SD/MMC cards can erase an arbitrarily large area up to and
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including the whole card. When erasing a large area it may
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be desirable to do it in smaller chunks for three reasons:
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1. A single erase command will make all other I/O on
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the card wait. This is not a problem if the whole card
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is being erased, but erasing one partition will make
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I/O for another partition on the same card wait for the
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duration of the erase - which could be a several
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minutes.
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2. To be able to inform the user of erase progress.
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3. The erase timeout becomes too large to be very
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useful. Because the erase timeout contains a margin
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which is multiplied by the size of the erase area,
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the value can end up being several minutes for large
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areas.
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"erase_size" is not the most efficient unit to erase
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(especially for SD where it is just one sector),
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hence "preferred_erase_size" provides a good chunk
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size for erasing large areas.
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For MMC, "preferred_erase_size" is the high-capacity
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erase size if a card specifies one, otherwise it is
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based on the capacity of the card.
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For SD, "preferred_erase_size" is the allocation unit
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size specified by the card.
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"preferred_erase_size" is in bytes.
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Note on raw_rpmb_size_mult:
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"raw_rpmb_size_mult" is a mutliple of 128kB block.
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RPMB size in byte is calculated by using the following equation:
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RPMB partition size = 128kB x raw_rpmb_size_mult
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SD/MMC/SDIO Clock Gating Attribute
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==================================
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Read and write access is provided to following attribute.
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This attribute appears only if CONFIG_MMC_CLKGATE is enabled.
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clkgate_delay Tune the clock gating delay with desired value in milliseconds.
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echo <desired delay> > /sys/class/mmc_host/mmcX/clkgate_delay
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SD/MMC/SDIO Clock Scaling Attributes
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====================================
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Read and write accesses are provided to following attributes.
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polling_interval Measured in milliseconds, this attribute
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defines how often we need to check the card
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usage and make decisions on frequency scaling.
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up_threshold This attribute defines what should be the
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average card usage between the polling
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interval for the mmc core to make a decision
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on whether it should increase the frequency.
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For example when it is set to '35' it means
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that between the checking intervals the card
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needs to be on average more than 35% in use to
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scale up the frequency. The value should be
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between 0 - 100 so that it can be compared
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against load percentage.
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down_threshold Similar to up_threshold, but on lowering the
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frequency. For example, when it is set to '2'
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it means that between the checking intervals
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the card needs to be on average less than 2%
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in use to scale down the clocks to minimum
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frequency. The value should be between 0 - 100
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so that it can be compared against load
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percentage.
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enable Enable clock scaling for hosts (and cards)
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that support ultrahigh speed modes
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(SDR104, DDR50, HS200).
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echo <desired value> > /sys/class/mmc_host/mmcX/clk_scaling/polling_interval
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echo <desired value> > /sys/class/mmc_host/mmcX/clk_scaling/up_threshold
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echo <desired value> > /sys/class/mmc_host/mmcX/clk_scaling/down_threshold
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echo <desired value> > /sys/class/mmc_host/mmcX/clk_scaling/enable
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