lkml.org 
[lkml]   [2018]   [Feb]   [27]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
SubjectRe: [PATCH v3 05/10] pwm: add PWM mode to pwm_config()
From
Date


On 27.02.2018 12:54, Daniel Thompson wrote:
> On Mon, Feb 26, 2018 at 04:24:15PM +0200, Claudiu Beznea wrote:
>> On 26.02.2018 11:57, Jani Nikula wrote:
>>> On Thu, 22 Feb 2018, Daniel Thompson <daniel.thompson@linaro.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@microchip.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?
>
> What is it that actually needs solving?
>
> If a driver requests normal mode and the PWM driver cannot support it
> why not just return an error an move on.
Because, simply, I wasn't aware of what these PWM client drivers needs for.

>
> Put another way, what is the use case for secretly adopting a mode the
> caller didn't want? Under what circumstances is this a good thing?
No one... But I wasn't aware of what the PWM clients needs for from their PWM
controllers. At this moment having BIT(ffs(caps.modes)) instead of
PWM_MODE(NORMAL) is mostly the same since all the driver that has not explicitly
registered PWM caps will use PWM normal mode.

I will use PWM_MODE(NORMAL) instead of this in all the cases if this is OK from
your side.

Thank you,
Claudiu Beznea
>
>
> Daniel.
>

\
 
 \ /
  Last update: 2018-02-27 12:41    [W:0.093 / U:0.232 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site