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| Started by | Maxime Ripard <maxime.ripard@free-electrons.com> |
|---|---|
| First post | 2017-05-29 09:50 +0200 |
| Last post | 2017-05-29 11:30 +0200 |
| Articles | 3 — 2 participants |
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Re: [PATCH 3/3] ARM: sun8i: v3s: add backlight device node for Lichee Pi Zero LCD Maxime Ripard <maxime.ripard@free-electrons.com> - 2017-05-29 09:50 +0200
Re: [PATCH 3/3] ARM: sun8i: v3s: add backlight device node for Lichee Pi Zero LCD Chen-Yu Tsai <wens@csie.org> - 2017-05-29 10:20 +0200
Re: [PATCH 3/3] ARM: sun8i: v3s: add backlight device node for Lichee Pi Zero LCD Maxime Ripard <maxime.ripard@free-electrons.com> - 2017-05-29 11:30 +0200
| From | Maxime Ripard <maxime.ripard@free-electrons.com> |
|---|---|
| Date | 2017-05-29 09:50 +0200 |
| Subject | Re: [PATCH 3/3] ARM: sun8i: v3s: add backlight device node for Lichee Pi Zero LCD |
| Message-ID | <tMnB8-56h-15@gated-at.bofh.it> |
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Hi,
On Wed, May 24, 2017 at 08:13:20PM +0800, Icenowy Zheng wrote:
> The 40-pin LCD connector on Lichee Pi Zero has backlight pins, which is
> controlled by the PWM0 controller of the V3s SoC, and the controlling
> part is on the board.
>
> Add the PWM and backlight device nodes in the device tree file, but
> leave them disabled, as they can only be useful when the LCD is
> attached. The LCD device tree overlay files can enable these controllers
> and make use of them.
>
> Signed-off-by: Icenowy Zheng <icenowy@aosc.io>
> ---
> arch/arm/boot/dts/sun8i-v3s-licheepi-zero.dts | 14 ++++++++++++++
> 1 file changed, 14 insertions(+)
>
> diff --git a/arch/arm/boot/dts/sun8i-v3s-licheepi-zero.dts b/arch/arm/boot/dts/sun8i-v3s-licheepi-zero.dts
> index 387fc2aa546d..e0721bf725d1 100644
> --- a/arch/arm/boot/dts/sun8i-v3s-licheepi-zero.dts
> +++ b/arch/arm/boot/dts/sun8i-v3s-licheepi-zero.dts
> @@ -52,6 +52,14 @@
> serial0 = &uart0;
> };
>
> + backlight: backlight {
> + compatible = "pwm-backlight";
> + pwms = <&pwm 0 50000 0>;
> + brightness-levels = <0 10 20 30 40 50 60 70 80 90 100>;
This is unlikely, the perceived brightness by the human eye is not
linear, and is actually much closer to a logarithmic function, which
means you should have use an exponential function here in order to
appear that your brightness increase is linear.
Maxime
--
Maxime Ripard, Free Electrons
Embedded Linux and Kernel engineering
http://free-electrons.com
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| From | Chen-Yu Tsai <wens@csie.org> |
|---|---|
| Date | 2017-05-29 10:20 +0200 |
| Subject | Re: [PATCH 3/3] ARM: sun8i: v3s: add backlight device node for Lichee Pi Zero LCD |
| Message-ID | <tMo49-5yh-7@gated-at.bofh.it> |
| In reply to | #1652260 |
On Mon, May 29, 2017 at 3:41 PM, Maxime Ripard
<maxime.ripard@free-electrons.com> wrote:
> Hi,
>
> On Wed, May 24, 2017 at 08:13:20PM +0800, Icenowy Zheng wrote:
>> The 40-pin LCD connector on Lichee Pi Zero has backlight pins, which is
>> controlled by the PWM0 controller of the V3s SoC, and the controlling
>> part is on the board.
>>
>> Add the PWM and backlight device nodes in the device tree file, but
>> leave them disabled, as they can only be useful when the LCD is
>> attached. The LCD device tree overlay files can enable these controllers
>> and make use of them.
>>
>> Signed-off-by: Icenowy Zheng <icenowy@aosc.io>
>> ---
>> arch/arm/boot/dts/sun8i-v3s-licheepi-zero.dts | 14 ++++++++++++++
>> 1 file changed, 14 insertions(+)
>>
>> diff --git a/arch/arm/boot/dts/sun8i-v3s-licheepi-zero.dts b/arch/arm/boot/dts/sun8i-v3s-licheepi-zero.dts
>> index 387fc2aa546d..e0721bf725d1 100644
>> --- a/arch/arm/boot/dts/sun8i-v3s-licheepi-zero.dts
>> +++ b/arch/arm/boot/dts/sun8i-v3s-licheepi-zero.dts
>> @@ -52,6 +52,14 @@
>> serial0 = &uart0;
>> };
>>
>> + backlight: backlight {
>> + compatible = "pwm-backlight";
>> + pwms = <&pwm 0 50000 0>;
>> + brightness-levels = <0 10 20 30 40 50 60 70 80 90 100>;
>
> This is unlikely, the perceived brightness by the human eye is not
> linear, and is actually much closer to a logarithmic function, which
> means you should have use an exponential function here in order to
> appear that your brightness increase is linear.
I think the backlight is a functional part of the panel. It probably
belongs in the panel's overlay.
ChenYu
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| From | Maxime Ripard <maxime.ripard@free-electrons.com> |
|---|---|
| Date | 2017-05-29 11:30 +0200 |
| Message-ID | <tMp9V-6ft-37@gated-at.bofh.it> |
| In reply to | #1652274 |
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On Mon, May 29, 2017 at 04:16:51PM +0800, Chen-Yu Tsai wrote:
> On Mon, May 29, 2017 at 3:41 PM, Maxime Ripard
> <maxime.ripard@free-electrons.com> wrote:
> > Hi,
> >
> > On Wed, May 24, 2017 at 08:13:20PM +0800, Icenowy Zheng wrote:
> >> The 40-pin LCD connector on Lichee Pi Zero has backlight pins, which is
> >> controlled by the PWM0 controller of the V3s SoC, and the controlling
> >> part is on the board.
> >>
> >> Add the PWM and backlight device nodes in the device tree file, but
> >> leave them disabled, as they can only be useful when the LCD is
> >> attached. The LCD device tree overlay files can enable these controllers
> >> and make use of them.
> >>
> >> Signed-off-by: Icenowy Zheng <icenowy@aosc.io>
> >> ---
> >> arch/arm/boot/dts/sun8i-v3s-licheepi-zero.dts | 14 ++++++++++++++
> >> 1 file changed, 14 insertions(+)
> >>
> >> diff --git a/arch/arm/boot/dts/sun8i-v3s-licheepi-zero.dts b/arch/arm/boot/dts/sun8i-v3s-licheepi-zero.dts
> >> index 387fc2aa546d..e0721bf725d1 100644
> >> --- a/arch/arm/boot/dts/sun8i-v3s-licheepi-zero.dts
> >> +++ b/arch/arm/boot/dts/sun8i-v3s-licheepi-zero.dts
> >> @@ -52,6 +52,14 @@
> >> serial0 = &uart0;
> >> };
> >>
> >> + backlight: backlight {
> >> + compatible = "pwm-backlight";
> >> + pwms = <&pwm 0 50000 0>;
> >> + brightness-levels = <0 10 20 30 40 50 60 70 80 90 100>;
> >
> > This is unlikely, the perceived brightness by the human eye is not
> > linear, and is actually much closer to a logarithmic function, which
> > means you should have use an exponential function here in order to
> > appear that your brightness increase is linear.
>
> I think the backlight is a functional part of the panel. It probably
> belongs in the panel's overlay.
Yeah, that's also true.
Maxime
--
Maxime Ripard, Free Electrons
Embedded Linux and Kernel engineering
http://free-electrons.com
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