linux-kernel - Re: [PATCH v3 05/10] pwm: add PWM mode to pwm

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Date:   Mon, 26 Feb 2018 11:57:25 +0200
From:   Jani Nikula <jani.nikula@...ux.intel.com>
To:     Daniel Thompson <daniel.thompson@...aro.org>,
        Claudiu Beznea <claudiu.beznea@...rochip.com>
Cc:     thierry.reding@...il.com, shc_work@...l.ru, kgene@...nel.org,
        krzk@...nel.org, linux@...linux.org.uk, mturquette@...libre.com,
        sboyd@...eaurora.org, joonas.lahtinen@...ux.intel.com,
        rodrigo.vivi@...el.com, airlied@...ux.ie, kamil@...as.org,
        b.zolnierkie@...sung.com, jdelvare@...e.com, linux@...ck-us.net,
        dmitry.torokhov@...il.com, rpurdie@...ys.net,
        jacek.anaszewski@...il.com, pavel@....cz, mchehab@...nel.org,
        sean@...s.org, lee.jones@...aro.org, jingoohan1@...il.com,
        milo.kim@...com, robh+dt@...nel.org, mark.rutland@....com,
        corbet@....net, nicolas.ferre@...rochip.com,
        alexandre.belloni@...e-electrons.com, linux-pwm@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-samsung-soc@...r.kernel.org, linux-clk@...r.kernel.org,
        intel-gfx@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org,
        linux-hwmon@...r.kernel.org, linux-input@...r.kernel.org,
        linux-leds@...r.kernel.org, linux-media@...r.kernel.org,
        linux-fbdev@...r.kernel.org, devicetree@...r.kernel.org,
        linux-doc@...r.kernel.org
Subject: Re: [PATCH v3 05/10] pwm: add PWM mode to pwm_config()

On Thu, 22 Feb 2018, Daniel Thompson <daniel.thompson@...aro.org> wrote:
> On Thu, Feb 22, 2018 at 02:01:16PM +0200, Claudiu Beznea wrote:
>> Add PWM mode to pwm_config() function. The drivers which uses pwm_config()
>> were adapted to this change.
>> 
>> Signed-off-by: Claudiu Beznea <claudiu.beznea@...rochip.com>
>> ---
>>  arch/arm/mach-s3c24xx/mach-rx1950.c  | 11 +++++++++--
>>  drivers/bus/ts-nbus.c                |  2 +-
>>  drivers/clk/clk-pwm.c                |  3 ++-
>>  drivers/gpu/drm/i915/intel_panel.c   | 17 ++++++++++++++---
>>  drivers/hwmon/pwm-fan.c              |  2 +-
>>  drivers/input/misc/max77693-haptic.c |  2 +-
>>  drivers/input/misc/max8997_haptic.c  |  6 +++++-
>>  drivers/leds/leds-pwm.c              |  5 ++++-
>>  drivers/media/rc/ir-rx51.c           |  5 ++++-
>>  drivers/media/rc/pwm-ir-tx.c         |  5 ++++-
>>  drivers/video/backlight/lm3630a_bl.c |  4 +++-
>>  drivers/video/backlight/lp855x_bl.c  |  4 +++-
>>  drivers/video/backlight/lp8788_bl.c  |  5 ++++-
>>  drivers/video/backlight/pwm_bl.c     | 11 +++++++++--
>>  drivers/video/fbdev/ssd1307fb.c      |  3 ++-
>>  include/linux/pwm.h                  |  6 ++++--
>>  16 files changed, 70 insertions(+), 21 deletions(-)
>> 
>> diff --git a/drivers/video/backlight/lm3630a_bl.c b/drivers/video/backlight/lm3630a_bl.c
>> index 2030a6b77a09..696fa25dafd2 100644
>> --- a/drivers/video/backlight/lm3630a_bl.c
>> +++ b/drivers/video/backlight/lm3630a_bl.c
>> @@ -165,8 +165,10 @@ static void lm3630a_pwm_ctrl(struct lm3630a_chip *pchip, int br, int br_max)
>>  {
>>  	unsigned int period = pchip->pdata->pwm_period;
>>  	unsigned int duty = br * period / br_max;
>> +	struct pwm_caps caps = { };
>>  
>> -	pwm_config(pchip->pwmd, duty, period);
>> +	pwm_get_caps(pchip->pwmd->chip, pchip->pwmd, &caps);
>> +	pwm_config(pchip->pwmd, duty, period, BIT(ffs(caps.modes) - 1));
>
> Well... I admit I've only really looked at the patches that impact 
> backlight but dispersing this really odd looking bit twiddling 
> throughout the kernel doesn't strike me a great API design.
>
> IMHO callers should not be required to find the first set bit in
> some specially crafted set of capability bits simply to get sane 
> default behaviour.

Agreed. IMHO the regular use case becomes rather tedious, ugly, and
error prone.

BR,
Jani.


-- 
Jani Nikula, Intel Open Source Technology Center