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Subject: [PATCH v5] arm64: dts: rockchip: Fix SD card init on rk3399-nanopi4
Date:   Sat, 16 Jul 2022 21:43:46 +0200
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To:     Robin Murphy <robin.murphy@arm.com>, wens@kernel.org,
        =?utf-8?Q?Heiko_St=C3=BCbner?= <heiko@sntech.de>,
        Markus Reichl <m.reichl@fivetechno.de>,
        linux-arm-kernel <linux-arm-kernel@lists.infradead.org>,
        "open list:ARM/Rockchip SoC..." <linux-rockchip@lists.infradead.org>,
        linux-kernel <linux-kernel@vger.kernel.org>,
        Linux MMC List <linux-mmc@vger.kernel.org>
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Precedence: bulk

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.

As a welcome side-effect, this change allows the SD card voltage to be
set back to 3.0V upon reboot, allowing bootloaders to use the card right
away, obsoleting further patching.

Signed-off-by: Christian Kohlsch=C3=BCtter <christian@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 =3D <1800000>;
 		regulator-max-microvolt =3D <1800000>;
 		regulator-name =3D "vcc1v8_s3";
-		vin-supply =3D <&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 =3D <&vcc_1v8>; // actual supply
+		vin-supply =3D <&vcc3v0_sd>;
 	};
=20
 	vcc3v0_sd: vcc3v0-sd {
@@ -70,7 +80,6 @@ vcc3v0_sd: vcc3v0-sd {
 		gpio =3D <&gpio0 RK_PA1 GPIO_ACTIVE_HIGH>;
 		pinctrl-names =3D "default";
 		pinctrl-0 =3D <&sdmmc0_pwr_h>;
-		regulator-always-on;
 		regulator-min-microvolt =3D <3000000>;
 		regulator-max-microvolt =3D <3000000>;
 		regulator-name =3D "vcc3v0_sd";
--=20
2.36.1