dt-bindings: Add Tegra SDHCI pad pdpu offset bindings

Add bindings documentation for pad pull up and pull down offset values to be
programmed before executing automatic pad drive strength calibration.
Signed-off-by: NAapo Vienamo <avienamo@nvidia.com>
Reviewed-by: NRob Herring <robh@kernel.org>
Acked-by: NThierry Reding <treding@nvidia.com>
Signed-off-by: NUlf Hansson <ulf.hansson@linaro.org>

Documentation/devicetree/bindings/mmc/nvidia,tegra20-sdhci.txt

@@ -45,6 +45,37 @@ Optional properties for Tegra210 and Tegra186:
   for controllers supporting multiple voltage levels. The order of names
   should correspond to the pin configuration states in pinctrl-0 and
   pinctrl-1.
+- nvidia,only-1-8-v : The presence of this property indicates that the
+  controller operates at a 1.8 V fixed I/O voltage.
+- nvidia,pad-autocal-pull-up-offset-3v3,
+  nvidia,pad-autocal-pull-down-offset-3v3 : Specify drive strength
+  calibration offsets for 3.3 V signaling modes.
+- nvidia,pad-autocal-pull-up-offset-1v8,
+  nvidia,pad-autocal-pull-down-offset-1v8 : Specify drive strength
+  calibration offsets for 1.8 V signaling modes.
+- nvidia,pad-autocal-pull-up-offset-3v3-timeout,
+  nvidia,pad-autocal-pull-down-offset-3v3-timeout : Specify drive
+  strength used as a fallback in case the automatic calibration times
+  out on a 3.3 V signaling mode.
+- nvidia,pad-autocal-pull-up-offset-1v8-timeout,
+  nvidia,pad-autocal-pull-down-offset-1v8-timeout : Specify drive
+  strength used as a fallback in case the automatic calibration times
+  out on a 1.8 V signaling mode.
+- nvidia,pad-autocal-pull-up-offset-sdr104,
+  nvidia,pad-autocal-pull-down-offset-sdr104 : Specify drive strength
+  calibration offsets for SDR104 mode.
+- nvidia,pad-autocal-pull-up-offset-hs400,
+  nvidia,pad-autocal-pull-down-offset-hs400 : Specify drive strength
+  calibration offsets for HS400 mode.
+
+  Notes on the pad calibration pull up and pulldown offset values:
+    - The property values are drive codes which are programmed into the
+      PD_OFFSET and PU_OFFSET sections of the
+      SDHCI_TEGRA_AUTO_CAL_CONFIG register.
+    - A higher value corresponds to higher drive strength. Please refer
+      to the reference manual of the SoC for correct values.
+    - The SDR104 and HS400 timing specific values are used in
+      corresponding modes if specified.
 
 Example:
 sdhci@700b0000 {
@@ -58,5 +89,9 @@ sdhci@700b0000 {
 	pinctrl-names = "sdmmc-3v3", "sdmmc-1v8";
 	pinctrl-0 = <&sdmmc1_3v3>;
 	pinctrl-1 = <&sdmmc1_1v8>;
+	nvidia,pad-autocal-pull-up-offset-3v3 = <0x00>;
+	nvidia,pad-autocal-pull-down-offset-3v3 = <0x7d>;
+	nvidia,pad-autocal-pull-up-offset-1v8 = <0x7b>;
+	nvidia,pad-autocal-pull-down-offset-1v8 = <0x7b>;
 	status = "disabled";
 };