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Documentation: mmc: sdhci-of-arasan: Add ability to export card clock

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Some SD/eMMC PHYs (like the PHY from Arasan that is designed to work
with arasan,sdhci-5.1) need to know the card clock frequency in order to
function properly.  Physically in a SoC this clock is exported from the
SDHCI IP block to the PHY IP block and the PHY needs to know the speed.
Let's export the SDHCI card clock using a standard device tree mechanism
so that the PHY can get access to it and query the card clock frequency.

Signed-off-by: Douglas Anderson <dianders@chromium.org>
Acked-by: Rob Herring <robh@kernel.org>
Reviewed-by: Heiko Stuebner <heiko@sntech.de>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
This commit is contained in:
Douglas Anderson 2016-06-20 10:56:49 -07:00 committed by Ulf Hansson
parent 3ea4666e8d
commit 6db90c5976
1 changed files with 8 additions and 0 deletions
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8
Documentation/devicetree/bindings/mmc/arasan,sdhci.txt
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@ -30,6 +30,12 @@ Optional Properties:
- arasan,soc-ctl-syscon: A phandle to a syscon device (see ../mfd/syscon.txt)
used to access core corecfg registers. Offsets of registers in this
syscon are determined based on the main compatible string for the device.
- clock-output-names: If specified, this will be the name of the card clock
which will be exposed by this device. Required if #clock-cells is
specified.
- #clock-cells: If specified this should be the value <0>. With this property
in place we will export a clock representing the Card Clock. This clock
is expected to be consumed by our PHY. You must also specify
Example:
sdhci@e0100000 {
@ -61,7 +67,9 @@ Example:
arasan,soc-ctl-syscon = <&grf>;
assigned-clocks = <&cru SCLK_EMMC>;
assigned-clock-rates = <200000000>;
clock-output-names = "emmc_cardclock";
phys = <&emmc_phy>;
phy-names = "phy_arasan";
#clock-cells = <0>;
status = "disabled";
};