linux-kernel - Re: [PATCH] arm64: dts: qcom: sdm845-db845c: Move LVS regulator nodes up

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Message-ID: <55f07600-3fa5-f3c2-eb3e-e87a57244812@linaro.org>
Date:   Wed, 7 Jun 2023 12:16:55 +0200
From:   Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To:     Amit Pundir <amit.pundir@...aro.org>
Cc:     Doug Anderson <dianders@...omium.org>,
        Mark Brown <broonie@...nel.org>,
        Bjorn Andersson <andersson@...nel.org>,
        Andy Gross <agross@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Konrad Dybcio <konrad.dybcio@...aro.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Caleb Connolly <caleb.connolly@...aro.org>,
        Conor Dooley <conor+dt@...nel.org>,
        regressions <regressions@...ts.linux.dev>,
        linux-arm-msm <linux-arm-msm@...r.kernel.org>,
        dt <devicetree@...r.kernel.org>,
        lkml <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] arm64: dts: qcom: sdm845-db845c: Move LVS regulator nodes
 up

On 07/06/2023 11:17, Amit Pundir wrote:
> On Wed, 7 Jun 2023 at 13:19, Krzysztof Kozlowski
> <krzysztof.kozlowski@...aro.org> wrote:
>>
>> On 07/06/2023 01:34, Doug Anderson wrote:
>>> Hi,
>>>
>>> On Fri, Jun 2, 2023 at 9:12 AM Amit Pundir <amit.pundir@...aro.org> wrote:
>>>>
>>>> Move lvs1 and lvs2 regulator nodes up in the rpmh-regulators
>>>> list to workaround a boot regression uncovered by the upstream
>>>> commit ad44ac082fdf ("regulator: qcom-rpmh: Revert "regulator:
>>>> qcom-rpmh: Use PROBE_FORCE_SYNCHRONOUS"").
>>>>
>>>> Without this fix DB845c fail to boot at times because one of the
>>>> lvs1 or lvs2 regulators fail to turn ON in time.
>>>>
>>>> Link: https://lore.kernel.org/all/CAMi1Hd1avQDcDQf137m2auz2znov4XL8YGrLZsw5edb-NtRJRw@mail.gmail.com/
>>>> Signed-off-by: Amit Pundir <amit.pundir@...aro.org>
>>>> ---
>>>>  arch/arm64/boot/dts/qcom/sdm845-db845c.dts | 24 +++++++++++-----------
>>>>  1 file changed, 12 insertions(+), 12 deletions(-)
>>>>
>>>> diff --git a/arch/arm64/boot/dts/qcom/sdm845-db845c.dts b/arch/arm64/boot/dts/qcom/sdm845-db845c.dts
>>>> index e14fe9bbb386..df2fde9063dc 100644
>>>> --- a/arch/arm64/boot/dts/qcom/sdm845-db845c.dts
>>>> +++ b/arch/arm64/boot/dts/qcom/sdm845-db845c.dts
>>>> @@ -301,6 +301,18 @@ regulators-0 {
>>>>                 vdd-l26-supply = <&vreg_s3a_1p35>;
>>>>                 vin-lvs-1-2-supply = <&vreg_s4a_1p8>;
>>>>
>>>> +               vreg_lvs1a_1p8: lvs1 {
>>>> +                       regulator-min-microvolt = <1800000>;
>>>> +                       regulator-max-microvolt = <1800000>;
>>>> +                       regulator-always-on;
>>>> +               };
>>>> +
>>>> +               vreg_lvs2a_1p8: lvs2 {
>>>> +                       regulator-min-microvolt = <1800000>;
>>>> +                       regulator-max-microvolt = <1800000>;
>>>> +                       regulator-always-on;
>>>> +               };
>>>> +
>>>>                 vreg_s3a_1p35: smps3 {
>>>>                         regulator-min-microvolt = <1352000>;
>>>>                         regulator-max-microvolt = <1352000>;
>>>> @@ -381,18 +393,6 @@ vreg_l26a_1p2: ldo26 {
>>>>                         regulator-max-microvolt = <1200000>;
>>>>                         regulator-initial-mode = <RPMH_REGULATOR_MODE_HPM>;
>>>>                 };
>>>> -
>>>> -               vreg_lvs1a_1p8: lvs1 {
>>>> -                       regulator-min-microvolt = <1800000>;
>>>> -                       regulator-max-microvolt = <1800000>;
>>>> -                       regulator-always-on;
>>>> -               };
>>>> -
>>>> -               vreg_lvs2a_1p8: lvs2 {
>>>> -                       regulator-min-microvolt = <1800000>;
>>>> -                       regulator-max-microvolt = <1800000>;
>>>> -                       regulator-always-on;
>>>> -               };
>>>
>>> This is a hack, but it at least feels less bad than reverting the
>>> async probe patch. I'll leave it to Bjorn to decide if he's OK with
>>> it. Personally, it feels like this would deserve a comment in the dts
>>> to document that these regulators need to be listed first.
>>>
>>> Ideally, we could still work towards a root cause. I added a few more
>>> ideas to help with root causing in reply to the original thread about
>>> this.
>>>
>>> https://lore.kernel.org/r/CAD=FV=UKyjRNZG-ED2meUAR9aXdco+AbUTHiKixTzjCkaJbjTg@mail.gmail.com/
>>
>> We do not shape DTS based on given OS behavior. AOSP needs this, BSD
>> needs that and Linux needs something else. Next time someone will move
>> these regulators down because on his system probing is from end of list,
>> not beginning and he has the same problem.
>>
>> No, really, are we going to reshuffle nodes because AOSP needs it?
> 
> Hi, other than the fact that I reproduced it on AOSP, there is nothing
> AOSP specific in this patch. I'm sure there may be another
> platforms/OS (which load kernel modules from a ramdisk) that may trip
> on this bug. But I can try reproducing it on an OS of your choice if
> it helps.

I wrote earlier imaginary system where RPM driver loads the regulators
from the end. It would require re-shuffling to previous order of the
nodes. Feel free to change the RPM drivers to simulate it and you should
see that your patch stops helping.

The problem looks like in missing consumers, missing probe dependencies
or something in the driver how it handles these.

DTS should not be used for solving OS related problems.

Best regards,
Krzysztof