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

[Arpit Saini <arpit.saini@oss.qualcomm.com>]

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:

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
│  └─────────────────────────────────┘                            └──────────────────────┘       │
│                                                                                                │
└────────────────────────────────────────────────────────────────────────────────────────────────┘

Thanks,
Arpit