Re: [PATCH] arm64: dts: rockchip: Add DSI LCD display on rk3576-evb1

On Wed, Jul 29, 2026 at 6:46 PM Heiko Stübner <[email protected]> wrote:
>
> Am Montag, 20. Oktober 2025, 14:31:12 Mitteleuropäische Sommerzeit schrieb Heiko Stuebner:
> > Am Montag, 20. Oktober 2025, 10:50:58 Mitteleuropäische Sommerzeit schrieb Alexey Charkov:
> > >
> > > On Mon, Oct 20, 2025 at 12:31 PM Heiko Stuebner <[email protected]> wrote:
> > > >
> > > > Am Montag, 20. Oktober 2025, 10:19:51 Mitteleuropäische Sommerzeit schrieb Alexey Charkov:
> > > > > On Thu, Sep 25, 2025 at 12:38 AM Alexey Charkov <[email protected]> wrote:
> > > > > >
> > > > > > Add support for the Rockchip W552793DBA-V10 LCD+touchscreen assembly which
> > > > > > comes physically attached to Rockchip RK3576 EVB1 boards.
> > > > > >
> > > > > > The display part is driven by the on-chip MIPI DSI controller, and the
> > > > > > touchscreen is connected over I2C.
> > > > > >
> > > > > > Signed-off-by: Alexey Charkov <[email protected]>
> > > > > > ---
> > > > > > Note that backlight support is left out for now, as it depends on PWM
> > > > > > support [0] which has not yet been merged.
> > > > > >
> > > > > > A workaround is simply `gpioset -c 0 13=1` to set the respective GPIO
> > > > > > pin high and thus to light up the display unconditionally.
> > > > > >
> > > > > > [0] https://lore.kernel.org/lkml/[email protected]/
> > > > > > ---
> > > > > >  arch/arm64/boot/dts/rockchip/rk3576-evb1-v10.dts | 89 ++++++++++++++++++++++++
> > > > > >  1 file changed, 89 insertions(+)
> > > > >
> > > > > Hi Heiko,
> > > > >
> > > > > Any thoughts about this one? Can we perhaps get it merged for -next?
> > > >
> > > > Does the gpio-backlight work on that device?
> > > > That would make the gpioset hack unnecessary.
> > >
> > > I've got a local patch using pwm-gpio and pwm-backlight as a stop-gap
> > > solution, but I don't think it's worth merging upstream, because the
> > > backlight is supposed to be driven by the hardware PWM on the same pin
> > > (not bit-banging the GPIO line). After all, Nicolas has been working on
> > > adding a proper hardware PWM driver for RK3576.
> > >
> > > The display itself works without PWM support, and so does the touchscreen.
> >
> > Right now, I don't think we have an actual timeline if/when Nicolas will
> > be able to work on the pwm again. So my idea was if we want to
> > integrate the baclight as you described below, to have an actual usable
> > display and then when the new pwm has landed switch over to that one?
>
> With the ELCE around the corner we're nearing the year-mark here ;-)
> (And I'm surprised, I remembered this pending patch)

I've been hoping that Nicolas' PWM series gets further along in the meantime :)

> So how about integrating your gpio-pwm backlight for the time being?

Could do that, but I'm worried if it would immediately become set in
stone because DT is ABI, making it hard to switch to a "proper"
hardware-driven PWM once Nicolas' series lands.

> Or alternatively just going with a gpio-backlight, like the Anbernic Vita did:
>
>         /*
>          * LEDs and Backlights can be controlled as a PWM, but PWM
>          * support is not yet available.
>          */
>         gpio_backlight: backlight {
>                 compatible = "gpio-backlight";
>                 gpios = <&gpio2 RK_PC4 GPIO_ACTIVE_HIGH>;
>                 pinctrl-0 = <&led_backlight_h>;
>                 pinctrl-names = "default";
>         };

In the case of RK3576 EVB1 enabling it at full power is eye-burning
bright, so some sort of PWM is definitely warranted.

Best regards,
Alexey

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