linux-kernel - Re: [PATCH] ARM: multi_v7_defconfig: switch CONFIG_PWM

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Message-ID: <7hk1kv79at.fsf@baylibre.com>
Date:   Thu, 29 Nov 2018 15:28:42 -0800
From:   Kevin Hilman <khilman@...libre.com>
To:     Martin Blumenstingl <martin.blumenstingl@...glemail.com>
Cc:     linux-amlogic@...ts.infradead.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux@...linux.org.uk
Subject: Re: [PATCH] ARM: multi_v7_defconfig: switch CONFIG_PWM_MESON to built-in

Martin Blumenstingl <martin.blumenstingl@...glemail.com> writes:

> Hi Kevin,
>
> On Thu, Nov 29, 2018 at 1:30 AM Kevin Hilman <khilman@...libre.com> wrote:
>>
>> Martin Blumenstingl <martin.blumenstingl@...glemail.com> writes:
>>
>> > Some Meson8b boards (Odroid-C1, EC-100) use a PWM regulator which is the
>> > voltage supply of the CPU cores (this regulator is typically called
>> > "VCCK").
>> > Now that we are preparing support for CPU frequency scaling on Meson8,
>> > Meson8b and Meson8m2 we should build the pwm-meson driver into the
>> > kernel so we can configure the CPU voltage early in the boot process.
>>
>> Can you explain a little more why the configuration of CPU voltage
>> cannot wait a bit so this could be properly probed?
>
> I was under the impression that cpufreq-dt would still initialize even
> if the regulator is not ready yet. however (after reading the code
> again) this is clearly NOT the case.

Hmm, a quick look at cpufreq-dt suggests that it should -EPROBE_DEFER if
the regulator isn't ready yet.  Why doesn't that work?

> there's still a benefit with this change: your Odroid-C1 in your
> KernelCI lab would also be able to change the CPU frequency (so in
> case something breaks we could spot it there).
> will you accept this patch after I updated the description to mention
> that it's for KernelCI test coverage?

Possibly, but I'd still rather see the dependencies worked out correctly
so that this can be module, and cpufreq-dt would defer until it's ready.

Kevin