RE: [PATCH v3] pwm_backlight: Add device tree support for LowThreshold Brightness

From: Philip, Avinash
Date: Thu Oct 11 2012 - 04:33:51 EST


On Fri, Sep 28, 2012 at 11:15:48, Thierry Reding wrote:
> On Thu, Sep 27, 2012 at 02:33:09PM -0700, Andrew Morton wrote:
> > On Wed, 26 Sep 2012 20:17:07 +0530
> > "Philip, Avinash" <avinashphilip@xxxxxx> wrote:
> >
> > > Some back lights perform poorly when driven by a PWM with a short
> > > duty-cycle. For such devices, the low threshold can be used to specify a
> > > lower bound for the duty-cycle and should be chosen to exclude the
> > > problematic range.
> > >
> > > Add device tree probing support for lth_brightness putting
> > > low-threshold-brightness as optional property.
> > >
> > > ...
> > >
> > > --- a/Documentation/devicetree/bindings/video/backlight/pwm-backlight.txt
> > > +++ b/Documentation/devicetree/bindings/video/backlight/pwm-backlight.txt
> > > @@ -14,6 +14,15 @@ Required properties:
> > > Optional properties:
> > > - pwm-names: a list of names for the PWM devices specified in the
> > > "pwms" property (see PWM binding[0])
> > > + - low-threshold-brightness: brightness threshold low level. Low threshold
> > > + brightness set to value so that backlight present on low end of
> > > + brightness.
> > > + Some panels, backlight would absent if duty percentage of PWM wave is less
> > > + than certain level (say 20%). By setting low-threshold-brightness to a
> > > + value above (percentage of brightness-levels max) 50 (20% of 255, if 255
> > > + is max). On setting low-threshold-brightness, range of brightness-levels
> > > + is calculated in a region of low-threshold-brightness to brightness-levels
> > > + max.
> >
> > hoo boy, that's hard to follow. How does this look?
> >
> > --- a/Documentation/devicetree/bindings/video/backlight/pwm-backlight.txt~pwm_backlight-add-device-tree-support-for-low-threshold-brightness-fix
> > +++ a/Documentation/devicetree/bindings/video/backlight/pwm-backlight.txt
> > @@ -14,15 +14,15 @@ Required properties:
> > Optional properties:
> > - pwm-names: a list of names for the PWM devices specified in the
> > "pwms" property (see PWM binding[0])
> > - - low-threshold-brightness: brightness threshold low level. Low threshold
> > - brightness set to value so that backlight present on low end of
> > - brightness.
> > - Some panels, backlight would absent if duty percentage of PWM wave is less
> > - than certain level (say 20%). By setting low-threshold-brightness to a
> > - value above (percentage of brightness-levels max) 50 (20% of 255, if 255
> > - is max). On setting low-threshold-brightness, range of brightness-levels
> > - is calculated in a region of low-threshold-brightness to brightness-levels
> > - max.
> > + - low-threshold-brightness: brightness threshold low level. Sets the lowest
> > + brightness value.
> > + On some panels the backlight misbehaves if the duty cycle percentage of the
> > + PWM wave is less than a certain level (say 20%). In this example the user
> > + can set low-threshold-brightness to a value above 50 (ie, 20% of 255), thus
> > + preventing the PWM duty cycle from going too low.
> > + On setting low-threshold-brightness the range of brightness levels is
> > + calculated in the range low-threshold-brightness to the maximum value in
> > + brightness-levels, described above.
> >
> > [0]: Documentation/devicetree/bindings/pwm/pwm.txt
> >
> >
> >
> > Also, I'm wondering if we really needed a new property - couldn't one
> > do this simply by setting brightness-levels to 50..255?
>
> Yes. This was discussed in the thread that followed the posting of this
> patch's v2. We've decided to drop it and go with brightness-levels only
> for device tree data. Eventually all existing users should convert to
> that as well so we can remove some of the cruft from the platform data
> up.

Andrew/Thierry,

It was decided that patch as dropped and still see it in linux-next.
http://git.kernel.org/?p=linux/kernel/git/next/linux-next.git;a=commit;h=1801ff7f87131190b0a469c26bd7c829601e198c

Thanks
Avinash

>
> Thierry
>

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/