Re: [RFC 1/2] arm64: dts: qcom: x1e78100-t14s: Add LCD variant with backlight support

[Sebastian Reichel]

Hi,

On Sun, Mar 09, 2025 at 11:19:52AM +0200, Abel Vesa wrote:
> On 25-03-08 01:01:31, Sebastian Reichel wrote:
> > Hi,
> > 
> > On Thu, Mar 06, 2025 at 11:05:02AM +0200, Abel Vesa wrote:
> > > Due to the fact that Lenovo Thinkpad T14s Gen6 is available with both
> > > OLED and LCD, the backlight control differs HW-wise. For the LCD variant,
> > > the panel's backlight is controlled via one of the PWMs provided by the
> > > PMK8550 PMIC. For the OLED variant, the backlight is internal to the
> > > panel and therefore it is not described in devicetree.
> > > 
> > > For this reason, create a generic dtsi for the T14s by renaming the
> > > existing dts. While at it, add a node name to panel and drop the enable
> > > gpio and pinctrl properties from the panel node. Then add the LCD variant
> > > dts file with the old name and describe all backlight related nodes.
> > > 
> > > So the existing dts will now be used for LCD variant while for OLED new
> > > dts will be added.
> > > 
> > > Signed-off-by: Abel Vesa <abel.vesa@xxxxxxxxxx>
> > > ---
> > > [...]
> > > +	backlight: backlight {
> > > +		compatible = "pwm-backlight";
> > > +		pwms = <&pmk8550_pwm 0 5000000>;
> > 
> > I've tried this patch series together with the fix series [0], but
> > without the duty cycle calculation change [1]. Instead I changed the
> > period from 5000000 to 4266667. With that everything works as
> > expected for me.
> > 
> > [0] https://lore.kernel.org/all/20250305-leds-qcom-lpg-fix-max-pwm-on-hi-res-v4-0-bfe124a53a9f@xxxxxxxxxx/
> > [1] https://lore.kernel.org/all/20250303-leds-qcom-lpg-compute-pwm-value-using-period-v1-1-833e729e3da2@xxxxxxxxxx/
> 
> Yes, I forgot to squash in the correct period.
> 
> The period should actually be 4266537. This is because the max PWM value
> is actually BIT(resolution) - 1.

For the version with 4266537:

Tested-by: Sebastian Reichel <sre@xxxxxxxxxx>

-- Sebastian

> 
> Will update in next version.
> 
> The [1] patch was basically NACKed by Uwe. It is not needed if we set
> the period to 4266537 in DT.
> 
> > 
> > Greetings,
> > 
> > -- Sebastian
> 
>

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