linux-kernel - Re: [PATCH v8 4/8] dt-bindings: pwm: Support new PWM_USAGE

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Message-ID: <YHmzNaxMjPJMcPmK@workstation.tuxnet>
Date:   Fri, 16 Apr 2021 17:54:29 +0200
From:   Clemens Gruber <clemens.gruber@...ruber.com>
To:     Thierry Reding <thierry.reding@...il.com>
Cc:     Rob Herring <robh+dt@...nel.org>, linux-pwm@...r.kernel.org,
        Sven Van Asbroeck <TheSven73@...il.com>,
        Uwe Kleine-König 
        <u.kleine-koenig@...gutronix.de>, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v8 4/8] dt-bindings: pwm: Support new PWM_USAGE_POWER flag

On Fri, Apr 16, 2021 at 03:55:11PM +0200, Thierry Reding wrote:
> On Mon, Apr 12, 2021 at 03:27:41PM +0200, Clemens Gruber wrote:
> > Add the flag and corresponding documentation for PWM_USAGE_POWER.
> > 
> > Cc: Rob Herring <robh+dt@...nel.org>
> > Signed-off-by: Clemens Gruber <clemens.gruber@...ruber.com>
> > ---
> >  Documentation/devicetree/bindings/pwm/pwm.txt | 3 +++
> >  include/dt-bindings/pwm/pwm.h                 | 1 +
> >  2 files changed, 4 insertions(+)
> 
> Rob, what are your thoughts on this? I've been thinking about this some
> more and I'm having second thoughts about putting this into device tree
> because it doesn't actually describe a property of the PWM hardware but
> rather a use-case specific hint. It's a bit of a gray area because this
> is just part of the PWM specifier which already has use-case specific
> "configuration", such as the period and the polarity.
> 
> Perhaps a better place for this is within the PWM API? We could add the
> same information into struct pwm_state and then consumers that don't
> care about specifics of the signal (such as pwm-backlight) can set that
> flag when they request a state to be applied.

I just want to note that in my opinion, this is not a flag that is
changed often, so is it really a good idea to require setting this
wherever PWM state is applied? Also, this can't be read-out in
.get_state.

Thierry: If this discussion carries on and a v10 is required: Could you
maybe merge the uncontroversial patches 1 to 3 of v9 separately and
maybe get those in 5.12 ? Patches 4 to 8 can probably wait for 5.13 and
have some time in linux-next.

Thanks,
Clemens