597dd9d79c
Current clock gating framework disables the MCI clock as soon as the request is completed and enables it when a request arrives. This aggressive clock gating framework, when enabled, cause following issues: When there are back-to-back requests from the Queue layer, we unnecessarily end up disabling and enabling the clocks between these requests since 8MCLK clock cycles is a very short duration compared to the time delay between back to back requests reaching the MMC layer. This overhead can effect the overall performance depending on how long the clock enable and disable calls take which is platform dependent. For example on some platforms we can have clock control not on the local processor, but on a different subsystem and the time taken to perform the clock enable/disable can add significant overhead. Also if the host controller driver decides to disable the host clock too when mmc_set_ios function is called with ios.clock=0, it adds additional delay and it is highly possible that the next request had already arrived and unnecessarily blocked in enabling the clocks. This is seen frequently when the processor is executing at high speeds and in multi-core platforms thus reduces the overall throughput compared to if clock gating is disabled. Fix this by delaying turning off the clocks by posting request on delayed workqueue. Also cancel the unscheduled pending work, if any, when there is access to card. sysfs entry is provided to tune the delay as needed, default value set to 200ms. Signed-off-by: Sujit Reddy Thumma <sthumma@codeaurora.org> Acked-by: Linus Walleij <linus.walleij@linaro.org> Signed-off-by: Chris Ball <cjb@laptop.org>
76 lines
2.8 KiB
Text
76 lines
2.8 KiB
Text
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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SD and MMC Device Attributes
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============================
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All attributes are read-only.
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cid Card Identifaction 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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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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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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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 milli seconds.
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echo <desired delay> > /sys/class/mmc_host/mmcX/clkgate_delay
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