From: Thierry Reding <thierry.reding@gmail.com>
To: "Uwe Kleine-König" <u.kleine-koenig@pengutronix.de>
Cc: Clemens Gruber <clemens.gruber@pqgruber.com>,
linux-pwm@vger.kernel.org,
Sven Van Asbroeck <TheSven73@gmail.com>,
devicetree@vger.kernel.org, linux-kernel@vger.kernel.org,
Rob Herring <robh+dt@kernel.org>
Subject: Re: [PATCH v8 4/8] dt-bindings: pwm: Support new PWM_USAGE_POWER flag
Date: Tue, 13 Apr 2021 13:51:15 +0200 [thread overview]
Message-ID: <YHWFs1f0XHkqbddp@orome.fritz.box> (raw)
In-Reply-To: <20210412162723.7hlhgqp6wlfbkeky@pengutronix.de>
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On Mon, Apr 12, 2021 at 06:27:23PM +0200, Uwe Kleine-König wrote:
> On Mon, Apr 12, 2021 at 03:27:41PM +0200, Clemens Gruber wrote:
> > Add the flag and corresponding documentation for PWM_USAGE_POWER.
>
> My concern here in the previous round was that PWM_USAGE_POWER isn't a
> name that intuitively suggests its semantic. Do you disagree?
I suggested PWM_USAGE_POWER because I think it accurately captures what
we want here.
> > Cc: Rob Herring <robh+dt@kernel.org>
> > Signed-off-by: Clemens Gruber <clemens.gruber@pqgruber.com>
> > ---
> > Documentation/devicetree/bindings/pwm/pwm.txt | 3 +++
> > include/dt-bindings/pwm/pwm.h | 1 +
> > 2 files changed, 4 insertions(+)
> >
> > diff --git a/Documentation/devicetree/bindings/pwm/pwm.txt b/Documentation/devicetree/bindings/pwm/pwm.txt
> > index 084886bd721e..fe3a28f887c0 100644
> > --- a/Documentation/devicetree/bindings/pwm/pwm.txt
> > +++ b/Documentation/devicetree/bindings/pwm/pwm.txt
> > @@ -46,6 +46,9 @@ period in nanoseconds.
> > Optionally, the pwm-specifier can encode a number of flags (defined in
> > <dt-bindings/pwm/pwm.h>) in a third cell:
> > - PWM_POLARITY_INVERTED: invert the PWM signal polarity
> > +- PWM_USAGE_POWER: Only care about the power output of the signal. This
> > + allows drivers (if supported) to optimize the signals, for example to
> > + improve EMI and reduce current spikes.
>
> IMHO there are too many open questions about which freedom this gives to
> the lowlevel driver. If the consumer requests .duty_cycle = 25ns +
> .period = 100ns, can the driver provide .duty_cycle = 25s + .period =
> 100s which nominally has the same power output? Let's not introduce more
> ambiguity than there already is.
The freedom given to the driver should be to adjust the signal within
reasonable bounds. Changing the time unit by a factor of 1000000000 is
not within reason, and I doubt anyone would interpret it that way, even
if we didn't document this at all.
To be frank I think that quest of yours to try and rid the PWM API of
all ambiguity is futile. I've been trying to be lenient because you seem
motivated, but I think you're taking this too far. There are always
going to be cases that aren't completely clear-cut and where drivers
need the flexibility to cheat in order to be useful at all. If we get to
a point where everything needs to be 100% accurate, the majority of the
PWM controllers won't be usable at all.
Don't let perfect be the enemy of good.
Thierry
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next prev parent reply other threads:[~2021-04-13 11:50 UTC|newest]
Thread overview: 42+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-04-12 13:27 [PATCH v8 1/8] pwm: pca9685: Switch to atomic API Clemens Gruber
2021-04-12 13:27 ` [PATCH v8 2/8] pwm: pca9685: Support hardware readout Clemens Gruber
2021-04-12 16:21 ` Uwe Kleine-König
2021-04-12 13:27 ` [PATCH v8 3/8] pwm: pca9685: Improve runtime PM behavior Clemens Gruber
2021-04-12 13:27 ` [PATCH v8 4/8] dt-bindings: pwm: Support new PWM_USAGE_POWER flag Clemens Gruber
2021-04-12 16:27 ` Uwe Kleine-König
2021-04-12 16:46 ` Clemens Gruber
2021-04-13 11:38 ` Uwe Kleine-König
2021-04-13 11:41 ` Thierry Reding
2021-04-13 11:51 ` Thierry Reding [this message]
2021-04-13 17:56 ` Uwe Kleine-König
2021-04-15 16:27 ` Thierry Reding
2021-04-16 9:32 ` Uwe Kleine-König
2021-04-16 10:45 ` Thierry Reding
2021-04-18 13:30 ` Uwe Kleine-König
2021-04-16 13:55 ` Thierry Reding
2021-04-16 15:39 ` Rob Herring
2021-04-16 15:54 ` Clemens Gruber
2021-04-17 15:44 ` Uwe Kleine-König
2021-04-12 13:27 ` [PATCH v8 5/8] pwm: core: " Clemens Gruber
2021-04-12 13:27 ` [PATCH v8 6/8] pwm: pca9685: " Clemens Gruber
2021-04-12 16:30 ` Uwe Kleine-König
2021-04-12 17:11 ` Clemens Gruber
2021-04-13 10:34 ` Uwe Kleine-König
2021-04-12 13:27 ` [PATCH v8 7/8] pwm: pca9685: Restrict period change for enabled PWMs Clemens Gruber
2021-04-17 15:46 ` Uwe Kleine-König
2021-04-12 13:27 ` [PATCH v8 8/8] pwm: pca9685: Add error messages for failed regmap calls Clemens Gruber
2021-04-17 15:47 ` Uwe Kleine-König
2021-04-12 16:18 ` [PATCH v8 1/8] pwm: pca9685: Switch to atomic API Uwe Kleine-König
2021-04-12 16:39 ` Clemens Gruber
2021-04-12 20:10 ` Uwe Kleine-König
2021-04-13 12:11 ` Clemens Gruber
2021-04-13 12:17 ` Clemens Gruber
2021-04-13 12:37 ` Thierry Reding
2021-04-13 13:06 ` Clemens Gruber
2021-04-13 19:38 ` Uwe Kleine-König
2021-04-14 12:09 ` Clemens Gruber
2021-04-14 19:21 ` Uwe Kleine-König
2021-04-14 19:45 ` Clemens Gruber
2021-04-15 6:48 ` Uwe Kleine-König
2021-04-17 15:37 ` Uwe Kleine-König
2021-04-17 16:40 ` Clemens Gruber
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