* [PATCH] backlight: pwm_bl: disable PWM when 'duty_cycle' is zero
@ 2016-06-06 10:44 Lothar Waßmann
2016-06-06 12:02 ` Tomi Valkeinen
0 siblings, 1 reply; 4+ messages in thread
From: Lothar Waßmann @ 2016-06-06 10:44 UTC (permalink / raw)
To: Jean-Christophe Plagniol-Villard, Jingoo Han, Lee Jones,
Thierry Reding, Tomi Valkeinen, linux-fbdev, linux-kernel,
linux-pwm
Cc: Lothar Waßmann
'brightness' is usually an index into a table of duty_cycle values,
where the value at index 0 may well be non-zero
(tegra30-apalis-eval.dts and tegra30-colibri-eval-v3.dts are real-life
examples).
Thus brightness == 0 does not necessarily mean that the PWM output
will be inactive.
Check for 'duty_cycle == 0' rather than 'brightness == 0' to decide
whether to disable the PWM.
Signed-off-by: Lothar Waßmann <LW@KARO-electronics.de>
---
drivers/video/backlight/pwm_bl.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/drivers/video/backlight/pwm_bl.c b/drivers/video/backlight/pwm_bl.c
index b2b366b..80b2b52 100644
--- a/drivers/video/backlight/pwm_bl.c
+++ b/drivers/video/backlight/pwm_bl.c
@@ -103,8 +103,8 @@ static int pwm_backlight_update_status(struct backlight_device *bl)
if (pb->notify)
brightness = pb->notify(pb->dev, brightness);
- if (brightness > 0) {
- duty_cycle = compute_duty_cycle(pb, brightness);
+ duty_cycle = compute_duty_cycle(pb, brightness);
+ if (duty_cycle > 0) {
pwm_config(pb->pwm, duty_cycle, pb->period);
pwm_backlight_power_on(pb, brightness);
} else
--
2.1.4
^ permalink raw reply related [flat|nested] 4+ messages in thread
* Re: [PATCH] backlight: pwm_bl: disable PWM when 'duty_cycle' is zero
2016-06-06 10:44 [PATCH] backlight: pwm_bl: disable PWM when 'duty_cycle' is zero Lothar Waßmann
@ 2016-06-06 12:02 ` Tomi Valkeinen
2016-06-07 6:49 ` Lothar Waßmann
0 siblings, 1 reply; 4+ messages in thread
From: Tomi Valkeinen @ 2016-06-06 12:02 UTC (permalink / raw)
To: Lothar Waßmann, Jean-Christophe Plagniol-Villard,
Jingoo Han, Lee Jones, Thierry Reding, linux-fbdev, linux-kernel,
linux-pwm
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Hi,
On 06/06/16 13:44, Lothar Waßmann wrote:
> 'brightness' is usually an index into a table of duty_cycle values,
> where the value at index 0 may well be non-zero
> (tegra30-apalis-eval.dts and tegra30-colibri-eval-v3.dts are real-life
> examples).
> Thus brightness == 0 does not necessarily mean that the PWM output
> will be inactive.
> Check for 'duty_cycle == 0' rather than 'brightness == 0' to decide
> whether to disable the PWM.
The binding doc does say:
- brightness-levels: Array of distinct brightness levels. Typically these
are in the range from 0 to 255, but any range starting at 0 will do.
The actual brightness level (PWM duty cycle) will be interpolated
from these values. 0 means a 0% duty cycle (darkest/off), while the
last value in the array represents a 100% duty cycle (brightest).
Tomi
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^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH] backlight: pwm_bl: disable PWM when 'duty_cycle' is zero
2016-06-06 12:02 ` Tomi Valkeinen
@ 2016-06-07 6:49 ` Lothar Waßmann
2016-06-07 8:02 ` Tomi Valkeinen
0 siblings, 1 reply; 4+ messages in thread
From: Lothar Waßmann @ 2016-06-07 6:49 UTC (permalink / raw)
To: Tomi Valkeinen
Cc: Jean-Christophe Plagniol-Villard, Jingoo Han, Lee Jones,
Thierry Reding, linux-fbdev, linux-kernel, linux-pwm
Hi,
On Mon, 6 Jun 2016 15:02:21 +0300 Tomi Valkeinen wrote:
> Hi,
>
> On 06/06/16 13:44, Lothar Waßmann wrote:
> > 'brightness' is usually an index into a table of duty_cycle values,
> > where the value at index 0 may well be non-zero
> > (tegra30-apalis-eval.dts and tegra30-colibri-eval-v3.dts are real-life
> > examples).
> > Thus brightness == 0 does not necessarily mean that the PWM output
> > will be inactive.
> > Check for 'duty_cycle == 0' rather than 'brightness == 0' to decide
> > whether to disable the PWM.
>
> The binding doc does say:
>
> - brightness-levels: Array of distinct brightness levels. Typically these
> are in the range from 0 to 255, but any range starting at 0 will do.
> The actual brightness level (PWM duty cycle) will be interpolated
> from these values. 0 means a 0% duty cycle (darkest/off), while the
> last value in the array represents a 100% duty cycle (brightest).
>
So, what should I do, when I need a range of levels that doesn't start
at 0? E.g. if the brightness is inverse proportional to the PWM duty
cycle.
Lothar Waßmann
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH] backlight: pwm_bl: disable PWM when 'duty_cycle' is zero
2016-06-07 6:49 ` Lothar Waßmann
@ 2016-06-07 8:02 ` Tomi Valkeinen
0 siblings, 0 replies; 4+ messages in thread
From: Tomi Valkeinen @ 2016-06-07 8:02 UTC (permalink / raw)
To: Lothar Waßmann
Cc: Jean-Christophe Plagniol-Villard, Jingoo Han, Lee Jones,
Thierry Reding, linux-fbdev, linux-kernel, linux-pwm
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On 07/06/16 09:49, Lothar Waßmann wrote:
> Hi,
>
> On Mon, 6 Jun 2016 15:02:21 +0300 Tomi Valkeinen wrote:
>> Hi,
>>
>> On 06/06/16 13:44, Lothar Waßmann wrote:
>>> 'brightness' is usually an index into a table of duty_cycle values,
>>> where the value at index 0 may well be non-zero
>>> (tegra30-apalis-eval.dts and tegra30-colibri-eval-v3.dts are real-life
>>> examples).
>>> Thus brightness == 0 does not necessarily mean that the PWM output
>>> will be inactive.
>>> Check for 'duty_cycle == 0' rather than 'brightness == 0' to decide
>>> whether to disable the PWM.
>>
>> The binding doc does say:
>>
>> - brightness-levels: Array of distinct brightness levels. Typically these
>> are in the range from 0 to 255, but any range starting at 0 will do.
>> The actual brightness level (PWM duty cycle) will be interpolated
>> from these values. 0 means a 0% duty cycle (darkest/off), while the
>> last value in the array represents a 100% duty cycle (brightest).
>>
> So, what should I do, when I need a range of levels that doesn't start
> at 0? E.g. if the brightness is inverse proportional to the PWM duty
> cycle.
That's a question to the PWM/backlight maintainers, but I think in the
addition of your patch, the binding doc needs to be changed, as it
doesn't hold true after your patch.
Tomi
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^ permalink raw reply [flat|nested] 4+ messages in thread
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2016-06-06 10:44 [PATCH] backlight: pwm_bl: disable PWM when 'duty_cycle' is zero Lothar Waßmann
2016-06-06 12:02 ` Tomi Valkeinen
2016-06-07 6:49 ` Lothar Waßmann
2016-06-07 8:02 ` Tomi Valkeinen
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