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authorSujit Reddy Thumma <sthumma@codeaurora.org>2011-11-14 13:53:29 +0530
committerChris Ball <cjb@laptop.org>2012-01-11 23:58:41 -0500
commit597dd9d79cfbbb1636d00a7fd0880355d9b20c41 (patch)
tree12911a3daaa38018d7ca1678fb28bb8c72536b68 /Documentation/mmc
parentc59d44739a8519cb7abdcd7cb7fd88f807dec9fd (diff)
downloadlinux-linaro-stable-597dd9d79cfbbb1636d00a7fd0880355d9b20c41.tar.gz
mmc: core: Use delayed work in clock gating framework
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>
Diffstat (limited to 'Documentation/mmc')
-rw-r--r--Documentation/mmc/mmc-dev-attrs.txt10
1 files changed, 10 insertions, 0 deletions
diff --git a/Documentation/mmc/mmc-dev-attrs.txt b/Documentation/mmc/mmc-dev-attrs.txt
index 8898a95b41e5..b0245565875a 100644
--- a/Documentation/mmc/mmc-dev-attrs.txt
+++ b/Documentation/mmc/mmc-dev-attrs.txt
@@ -64,3 +64,13 @@ Note on Erase Size and Preferred Erase Size:
size specified by the card.
"preferred_erase_size" is in bytes.
+
+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 milli seconds.
+
+echo <desired delay> > /sys/class/mmc_host/mmcX/clkgate_delay