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

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Message-ID: <3a70b89c-b470-3723-760c-5294d0a75230@microchip.com>
Date:   Mon, 26 Feb 2018 16:24:15 +0200
From:   Claudiu Beznea <Claudiu.Beznea@...rochip.com>
To:     Jani Nikula <jani.nikula@...ux.intel.com>,
        Daniel Thompson <daniel.thompson@...aro.org>
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 26.02.2018 11:57, Jani Nikula wrote:
> 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.

Using simply PWM_MODE(NORMAL) instead of BIT(ffs(caps.modes) - 1) would be OK
from your side?

Or, what about using a function like pwm_mode_first() to get the first supported
mode by PWM channel?

Or, would you prefer to solve this inside pwm_config() function, let's say, in
case an invalid mode is passed as argument, to let pwm_config() to choose the
first available PWM mode for PWM channel passed as argument?

Thank you,
Claudiu Beznea

> 
> BR,
> Jani.
> 
>