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Subject: Re: [PATCH v4] arm64: dts: rockchip: Fix SD card init on
 rk3399-nanopi4
From:   =?utf-8?Q?Christian_Kohlsch=C3=BCtter?= 
        <christian@kohlschutter.com>
In-Reply-To: <73F9AED0-D2A8-4294-B6E1-1B92D2A36529@kohlschutter.com>
Date:   Fri, 15 Jul 2022 19:16:20 +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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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

OK, this took me a while to figure out.

When no undervoltage limit is configured, I can reliably trigger the =
initialization bug upon boot.
When the limit is set to 3.0V, it rarely occurs, but just after I send =
the v3 patch, I was able to reproduce...

> Am 15.07.2022 um 19:12 schrieb Christian Kohlsch=C3=BCtter =
<christian@kohlschutter.com>:
>=20
> 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.
>=20
> Moreover, the system would also sometimes hang upon reboot.
>=20
> This is prevented by setting an explicit undervoltage protection limit
> for the SD-card-specific vcc3v0_sd voltage regulator.
>=20
> Set the undervoltage protection limit to 2.7V, which is the minimum
> permissible SD card operating voltage.
>=20
> 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
>=20
> 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 configured or SD card may fail to initialize =
occasionally
> +		regulator-uv-protection-microvolt =3D <2700000>;
> +
> 		regulator-name =3D "vcc3v0_sd";
> 		vin-supply =3D <&vcc3v3_sys>;
> 	};
> --=20
> 2.36.1