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Subject: [PATCH v3] arm64: dts: rockchip: Fix SD card init on rk3399-nanopi4
From:   =?utf-8?Q?Christian_Kohlsch=C3=BCtter?= 
        <christian@kohlschutter.com>
In-Reply-To: <502b3fbe-3077-407e-6010-a8cb3ffce7d6@arm.com>
Date:   Fri, 15 Jul 2022 19:01:02 +0200
Cc:     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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Message-Id: <449292CA-CE60-4B90-90F7-295FBFEAB3F8@kohlschutter.com>
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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>
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 prevented by setting an explicit undervoltage protection limit
for the SD-card-specific vcc3v0_sd voltage regulator.

While using a limit of 3V seems to work, an additional safety buffer
should prevent accidental tripping, preventing a system hang.

Set the undervoltage protection limit to 2.7V, which is the minimum
permissible SD card operating voltage.

Signed-off-by: Christian Kohlsch=C3=BCtter <christian@kohlschutter.com>
---
 arch/arm64/boot/dts/rockchip/rk3399-nanopi4.dtsi | 4 ++++
 1 file changed, 4 insertions(+)
 mode change 100644 =3D> 100755 =
arch/arm64/boot/dts/rockchip/rk3399-nanopi4.dtsi

diff --git a/arch/arm64/boot/dts/rockchip/rk3399-nanopi4.dtsi =
b/arch/arm64/boot/dts/rockchip/rk3399-nanopi4.dtsi
old mode 100644
new mode 100755
index 8c0ff6c96e03..669c74ce4d13
--- a/arch/arm64/boot/dts/rockchip/rk3399-nanopi4.dtsi
+++ b/arch/arm64/boot/dts/rockchip/rk3399-nanopi4.dtsi
@@ -73,6 +73,10 @@ vcc3v0_sd: vcc3v0-sd {
 		regulator-always-on;
 		regulator-min-microvolt =3D <3000000>;
 		regulator-max-microvolt =3D <3000000>;
+
+		// must be initialized or SD card may fail to initialize =
/ system may hang
+		regulator-uv-protection-microvolt =3D <2700000>;
+
 		regulator-name =3D "vcc3v0_sd";
 		vin-supply =3D <&vcc3v3_sys>;
 	};
--=20
2.36.1