[PATCH v6] arm64: dts: rockchip: Fix SD card init on rk3399-nanopi4

[Christian Kohlschütter]

mmc/SD-card initialization may fail on NanoPi R4S with
"mmc1: problem reading SD Status register" /
"mmc1: error -110 whilst initialising SD card"
either on cold boot or after a reboot.

Moreover, the system would also sometimes hang upon reboot.

This is caused by vcc3v0-sd's "regulator-always-on", which triggers
an erroneous double-initialization of the regulator. This causes
voltage fluctuations that can, depending on timing, prevent the
SD card from initializing correctly.

Adding some liberal delay via "off-on-delay-us" is ineffective since
that codepath is skipped as long "regulator-always-on" is set.

Removing "regulator-always-on" alone is not sufficient because that
would allow the system to set GPIO0_A1 to LOW upon reboot, which may
cause the system to hang.

In order to allow the system to set GPIO0_A1 to HIGH upon initialization
but prevent it from changing it back to LOW, this patch increases the
usage count of vcc3v0-sd from 1 to 2, whereas the additional reference,
"vcc1v8_s3", is marked as "always-on", causing permanent retention.

Signed-off-by: Christian Kohlschütter <christian at kohlschutter.com>
---
arch/arm64/boot/dts/rockchip/rk3399-nanopi4.dtsi | 13 +++++++++++--
1 file changed, 11 insertions(+), 2 deletions(-)

diff --git a/arch/arm64/boot/dts/rockchip/rk3399-nanopi4.dtsi b/arch/arm64/boot/dts/rockchip/rk3399-nanopi4.dtsi
index 8c0ff6c96e03..38507a6e3046 100644
--- a/arch/arm64/boot/dts/rockchip/rk3399-nanopi4.dtsi
+++ b/arch/arm64/boot/dts/rockchip/rk3399-nanopi4.dtsi
@@ -61,7 +61,17 @@ vcc1v8_s3: vcc1v8-s3 {
		regulator-min-microvolt = <1800000>;
		regulator-max-microvolt = <1800000>;
		regulator-name = "vcc1v8_s3";
-		vin-supply = <&vcc_1v8>;
+
+		/*
+		 * Workaround to skip setting gpio0 RK_PA1 to LOW upon reboot,
+		 * which may freeze the system.
+		 *
+		 * Adding a reference to vcc3v0_sd increases its num_users
+		 * count to 2, preventing deactivation since this regulator is
+		 * marked "always-on".
+		 */
+		// vin-supply = <&vcc_1v8>; // actual supply
+		vin-supply = <&vcc3v0_sd>;
	};

	vcc3v0_sd: vcc3v0-sd {
@@ -70,7 +80,6 @@ vcc3v0_sd: vcc3v0-sd {
		gpio = <&gpio0 RK_PA1 GPIO_ACTIVE_HIGH>;
		pinctrl-names = "default";
		pinctrl-0 = <&sdmmc0_pwr_h>;
-		regulator-always-on;
		regulator-min-microvolt = <3000000>;
		regulator-max-microvolt = <3000000>;
		regulator-name = "vcc3v0_sd";
-- 
2.36.1