mmc: dw_mmc: Add support for IMG Pistachio

Add support for the DW MMC host found on the Imagination Pistachio SoC.
Like the DW MMC hosts found on SOCFPGA and Rockchip SoCs, the DW MMC
host on Pistachio requires the use of SDMMC_CMD_USE_HOLD_REG.
Signed-off-by: Andrew Bresticker <abrestic@chromium.org>
Reviewed-by: Doug Anderson <dianders@chromium.org>
Acked-by: Jaehoon Chung <jh80.chung@samsung.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>

Documentation/devicetree/bindings/mmc/img-dw-mshc.txt

+* Imagination specific extensions to the Synopsys Designware Mobile Storage
+  Host Controller
+
+The Synopsys designware mobile storage host controller is used to interface
+a SoC with storage medium such as eMMC or SD/MMC cards. This file documents
+differences between the core Synopsys dw mshc controller properties described
+by synopsys-dw-mshc.txt and the properties used by the Imagination specific
+extensions to the Synopsys Designware Mobile Storage Host Controller.
+
+Required Properties:
+
+* compatible: should be
+	- "img,pistachio-dw-mshc": for Pistachio SoCs
+
+Example:
+
+	mmc@18142000 {
+		compatible = "img,pistachio-dw-mshc";
+		reg = <0x18142000 0x400>;
+		interrupts = <GIC_SHARED 39 IRQ_TYPE_LEVEL_HIGH>;
+
+		clocks = <&system_clk>, <&sdhost_clk>;
+		clock-names = "biu", "ciu";
+
+		fifo-depth = <0x20>;
+		bus-width = <4>;
+		num-slots = <1>;
+		disable-wp;
+	};

drivers/mmc/host/dw_mmc-pltfm.c

@@ -35,6 +35,10 @@ static const struct dw_mci_drv_data socfpga_drv_data = {
 	.prepare_command	= dw_mci_pltfm_prepare_command,
 };
 
+static const struct dw_mci_drv_data pistachio_drv_data = {
+	.prepare_command	= dw_mci_pltfm_prepare_command,
+};
+
 int dw_mci_pltfm_register(struct platform_device *pdev,
 			  const struct dw_mci_drv_data *drv_data)
 {
@@ -90,6 +94,8 @@ static const struct of_device_id dw_mci_pltfm_match[] = {
 	{ .compatible = "snps,dw-mshc", },
 	{ .compatible = "altr,socfpga-dw-mshc",
 		.data = &socfpga_drv_data },
+	{ .compatible = "img,pistachio-dw-mshc",
+		.data = &pistachio_drv_data },
 	{},
 };
 MODULE_DEVICE_TABLE(of, dw_mci_pltfm_match);