dt-bindings: mmc: sdhci-msm: Add clk scaling dt parameters

Add SD/eMMC clock scaling DT parameters.

Change-Id: I7a196deffa2f6ae582a882189efb79bb435a931d

bindings/mmc/sdhci-msm.txt

@@ -39,6 +39,21 @@ Required properties:
 	"cal"	- reference clock for RCLK delay calibration (optional)
 	"sleep"	- sleep clock for RCLK delay calibration (optional)
 
+Optional properties:
+- devfreq,freq-table - specifies supported frequencies for clock scaling.
+	Clock scaling logic shall toggle between these frequencies based
+	on card load. In case the defined frequencies are over or below
+	the supported card frequencies, they will be overridden
+	during card init. In case this entry is not supplied,
+	the driver will construct one based on the card
+	supported max and min frequencies.
+	The frequencies must be ordered from lowest to highest.
+
+- scaling-lower-bus-speed-mode - Few hosts can support DDR52 mode at the
+	same lower system voltage corner as high-speed mode. In such
+	cases, it is always better to put it in DDR  mode which will
+	improve the performance without any power impact.
+
 Example:
 
 	sdhc_1: sdhci@f9824900 {
@@ -73,4 +88,7 @@ Example:
 
 		clocks = <&gcc GCC_SDCC2_APPS_CLK>, <&gcc GCC_SDCC2_AHB_CLK>;
 		clock-names = "core", "iface";
+
+		qcom,devfreq,freq-table = <50000000 200000000>;
+		qcom,scaling-lower-bus-speed-mode = "DDR52";
 	};