Messages in this thread | | | Date | Fri, 15 Jul 2022 19:11:39 +0100 | Subject | Re: [PATCH v4] arm64: dts: rockchip: Fix SD card init on rk3399-nanopi4 | From | Robin Murphy <> |
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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@kohlschutter.com>: >> >> 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@kohlschutter.com> >> --- >> 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 >
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