Re: [PATCH v4] arm64: dts: rockchip: Fix SD card init on rk3399-nanopi4

[Robin Murphy]

On 2022-07-15 18:16, Christian Kohlschütter wrote:
> 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...

Well this has to be in the running for "weirdest placebo ever"... :/

All it actually seems to achieve is printing an error[1] (this is after 
all a tiny 5-pin fixed-voltage LDO regulator, not an intelligent PMIC), 
and if that makes an appreciable difference then there has to be some 
kind of weird timing condition at play. Maybe regulator_register() ends 
up turning it off and on again rapidly enough that the card sees a 
voltage brownout and glitches, and adding more delay by printing to the 
console somewhere in the middle gives it enough time to act as a proper 
power cycle with no ill effect?

If you just whack something like an mdelay(500) at around that point in 
set_machine_constraints(), without the DT property, does it have the 
same effect?

Robin.

[1] 
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/regulator/core.c#n1521

> > Am 15.07.2022 um 19:12 schrieb Christian Kohlschütter <christian@xxxxxxxxxxxxxxxx>:
> >
> > 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.
> >
> > Set the undervoltage protection limit to 2.7V, which is the minimum
> > permissible SD card operating voltage.
> >
> > Signed-off-by: Christian Kohlschütter <christian@xxxxxxxxxxxxxxxx>
> > ---
> > arch/arm64/boot/dts/rockchip/rk3399-nanopi4.dtsi | 4 ++++
> > 1 file changed, 4 insertions(+)
> > mode change 100644 => 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 = <3000000>;
> > 		regulator-max-microvolt = <3000000>;
> > +
> > +		// must be configured or SD card may fail to initialize occasionally
> > +		regulator-uv-protection-microvolt = <2700000>;
> > +
> > 		regulator-name = "vcc3v0_sd";
> > 		vin-supply = <&vcc3v3_sys>;
> > 	};
> > --
> > 2.36.1