arm64: dts: rockchip: Fix sdmmc access on rk3308-rock-s0 v1.1 boards

BootROM leave GPIO4_D6 configured as SDMMC_PWREN function and DW MCI
driver set PRWEN high on MMC_POWER_UP and low on MMC_POWER_OFF.
Similarly U-Boot also set PRWEN high before accessing mmc.

However, HW revision prior to v1.2 must pull GPIO4_D6 low to access
sdmmc. For HW revision v1.2 the state of GPIO4_D6 has no impact.

Model an always-on active low fixed regulator using GPIO4_D6 to fix
use of sdmmc on older HW revisions of the board.

Fixes: adeb5d2a4ba4 ("arm64: dts: rockchip: Add Radxa ROCK S0")
Signed-off-by: Jonas Karlman <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Heiko Stuebner <[email protected]>

[ upstream commit: 26c100232b09ced0857306ac9831a4fa9c9aa231 ]

(cherry picked from commit ca8e0bedbc790b19b11efc223677d178b8eeb74e)
Signed-off-by: Jonas Karlman <[email protected]>

Author: Kwiboo

dts/upstream/src/arm64/rockchip/rk3308-rock-s0.dts

@@ -74,6 +74,23 @@
 		vin-supply = <&vcc5v0_sys>;
 	};
 
+	/*
+	 * HW revision prior to v1.2 must pull GPIO4_D6 low to access sdmmc.
+	 * This is modeled as an always-on active low fixed regulator.
+	 */
+	vcc_sd: regulator-3v3-vcc-sd {
+		compatible = "regulator-fixed";
+		gpios = <&gpio4 RK_PD6 GPIO_ACTIVE_LOW>;
+		pinctrl-names = "default";
+		pinctrl-0 = <&sdmmc_2030>;
+		regulator-name = "vcc_sd";
+		regulator-always-on;
+		regulator-boot-on;
+		regulator-min-microvolt = <3300000>;
+		regulator-max-microvolt = <3300000>;
+		vin-supply = <&vcc_io>;
+	};
+
 	vcc5v0_sys: regulator-5v0-vcc-sys {
 		compatible = "regulator-fixed";
 		regulator-name = "vcc5v0_sys";
@@ -181,6 +198,12 @@
 		};
 	};
 
+	sdmmc {
+		sdmmc_2030: sdmmc-2030 {
+			rockchip,pins = <4 RK_PD6 RK_FUNC_GPIO &pcfg_pull_none>;
+		};
+	};
+
 	wifi {
 		wifi_reg_on: wifi-reg-on {
 			rockchip,pins = <0 RK_PA2 RK_FUNC_GPIO &pcfg_pull_none>;
@@ -233,7 +256,7 @@
 	cap-mmc-highspeed;
 	cap-sd-highspeed;
 	disable-wp;
-	vmmc-supply = <&vcc_io>;
+	vmmc-supply = <&vcc_sd>;
 	status = "okay";
 };