Re: [PATCH v2 2/4] arm64: dts: qcom: shikra-cqm-evk: Enable display and add ili7807s panel

[Dmitry Baryshkov]

On Mon, Jul 20, 2026 at 05:37:25PM +0530, Arpit Saini wrote:
> Hi Konrad,
> 
> On 7/16/2026 11:21 PM, Konrad Dybcio wrote:
> > On 7/14/26 9:21 AM, Arpit Saini wrote:
> >> Hi Dmitry,Konrad
> >>
> >> On 7/10/2026 6:09 PM, Dmitry Baryshkov wrote:
> >>> On Fri, Jul 10, 2026 at 05:28:04PM +0530, Arpit Saini wrote:
> >>>> Hi Konrad,
> >>>>
> >>>> On 7/10/2026 2:31 PM, Arpit Saini wrote:
> > 
> > [...]
> > 
> >>>> Normally the backlight EN pin is controlled by a backlight driver.
> >>>>
> >>>> However, this panel uses MIPI DCS based backlight control with no
> >>>>
> >>>> separate backlight driver. Since there is no driver to assert gpio91,
> >>>>
> >>>> we control it via the panel's pinctrl default state..
> >>>>
> >>>> So this is platform specific pin , we need this to enable/disable
> >>>>
> >>>> the backlight.
> >>>
> >>> Handle it from the panel driver. Also please fix your editor to prevent
> >>> it from inserting extra empty lines.
> >>>
> >>
> >> Earlier I handled it through panel driver, but this GPIO is specific to our
> >> Qualcomm Daughter Card, it is not going to the panel connector.
> > 
> > So is it an enable pin of a voltage regulator maybe? I'm having trouble
> > understanding how this is all tied together, given the panel driver
> > uses DCS commands to control the backlight status
> > 
> > Konrad
> 
> No, it is not a voltage regulator enable.
> GPIO91 (WLED_P1_EN) is the enable pin of the WLED driver IC on the Qualcomm daughter card.
> The WLED driver is a boost LED driver that powers the backlight LEDs.
> The backlight control works in two parts:

_that powers the backlight LEDs_.

So it is a power supply.

> 
> 1. GPIO91 must be asserted to enable the WLED driver IC itself.
> 2. The panel's CABC output (a PWM signal) is connected to the WLED driver's PWM input
> and controls the actual brightness.
> This CABC output is driven by the DCS set_display_brightness command sent from the panel driver.
> 
> So the DCS commands control brightness via the panel's PWM/CABC output,
> but the WLED driver IC needs to be enabled first via GPIO91.
> 
> Since GPIO91 is on the Qualcomm daughter card and not on the panel connector.
> 
> Dmitry suggested , it is not appropriate to model it in the panel binding.
> The current approach of asserting it via pinctrl default state in the board DTS keeps it board-specific.
> 
> If you have a better suggestion for modelling this, I'm happy to follow your guidance.
> 
> SoC (ITP Baseband Card)
>  ├── GPIO91 (WLED_P1_EN) ─────────────────────────────────────┐
>  │                                                            │
>  └── DSI ──────────────────────────────────────────────────┐  │
>                                                            │  │
> ┌──────────────────────────────────────────────────────────┼──┼──────────────────────────────────┐
> │ Qualcomm Display Daughter Card                           │  │                                  │
> │                                                          │  │                                  │
> │  ┌─────────────────────────────────┐                     │  │   ┌──────────────────────┐       │
> │  │  DLC DLC0697 Panel (ILI7807S)   │◄────────────────────┘  │   │  WLED Driver IC      │       │
> │  │                                 │                        |   │                      │       │
> │  │  DCS set_display_brightness()   │                        └──►│  EN                  │       │
> │  │        │                        │                            │                      │       │
> │  │        ▼                        │                            │                      │       │
> │  │  CABC output ───────────────────┼───────────────────────────►│  PWM                 │       │
> │  │                                 │                            │                      │       │
> │  │                                 │                            │  LED outputs ────────┼──► Backlight LEDs
> │  └─────────────────────────────────┘                            └──────────────────────┘       │
> │                                                                                                │
> └────────────────────────────────────────────────────────────────────────────────────────────────┘

This is a nice diagram, but it shows backlight LEDs as something
completely separate. Usually they are a part of the panel. Are they not
in this case?

I'd be more interested in a different representation of the information.
What are the _actual_ panel inputs? Decribe those (and only those) in
the panel bindings.

-- 
With best wishes
Dmitry