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

[Robin Murphy <robin.murphy@arm.com>]

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On 2022-07-15 19:11, Robin Murphy wrote:
> 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?

...and apparently the answer is yes, it seems to be doing exactly that 
(see attached). But seemingly my SD cards don't mind, or maybe my T4 
board happens to have more capacitance than Christian's R4S so my 
voltage dip isn't as bad, or both.

So it seems like the solution here might indeed simply be to remove the 
regulator-always-on which doesn't seem to have any reason to be here 
anyway. Without that, the enable stays low until the MMC driver probes 
and claims it, which is then massively longer than the time it takes for 
VCC3V0_SD to ramp down completely.

Robin.

> 
> 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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