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

["Heiko Stübner" <heiko@sntech.de>]

Am Mittwoch, 29. Juli 2026, 18:32:08 Mitteleuropäische Sommerzeit schrieb Alexey Charkov:
> On Wed, Jul 29, 2026 at 6:46 PM Heiko Stübner <heiko@sntech.de> 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 <heiko@sntech.de> 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 <alchark@gmail.com> 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 <alchark@gmail.com>
> > > > > > > ---
> > > > > > > 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/20250602-rk3576-pwm-v2-0-a6434b0ce60c@collabora.com/
> > > > > > > ---
> > > > > > >  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.

The backlight subsystem is using dev_name() to name the sysfs node.
So if you keep the node name to "backlight", the backlight device stays the
same.

I guess the question is if you also consider the brightness levels as
unchangeable, though I would assume any sane system should just read
max_brightness and adjust accordingly.

Also this is an eval-board ... so you won't have any actual real-world
users :-) .

So, personally I don't see the big hickup here, but we'll do what you
think best.


Heiko

> > 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
>