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

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Message-ID: <20210412162723.7hlhgqp6wlfbkeky@pengutronix.de>
Date:   Mon, 12 Apr 2021 18:27:23 +0200
From:   Uwe Kleine-König <u.kleine-koenig@...gutronix.de>
To:     Clemens Gruber <clemens.gruber@...ruber.com>
Cc:     linux-pwm@...r.kernel.org,
        Thierry Reding <thierry.reding@...il.com>,
        Sven Van Asbroeck <TheSven73@...il.com>,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        Rob Herring <robh+dt@...nel.org>
Subject: Re: [PATCH v8 4/8] dt-bindings: pwm: Support new PWM_USAGE_POWER flag

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?

> 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(+)
> 
> 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.

This is a NAck.

Best regards
Uwe

-- 
Pengutronix e.K.                           | Uwe Kleine-König            |
Industrial Linux Solutions                 | https://www.pengutronix.de/ |

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