Re: [PATCH v2 2/4] arm64: dts: qcom: shikra-cqm-evk: Enable display and add ili7807s panel
From: Arpit Saini
Date: Tue Jul 21 2026 - 05:13:01 EST
Hi Dmitry,
On 7/20/2026 6:35 PM, Dmitry Baryshkov wrote:
> 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.
>
No , Backlight LEDs are part of the panel, I will correct the diagram for that,
and regards panel bindings, I modeled only the actual panel inputs.
Hopefully, this diagram will clear this.
┌─────────────────┐ ┌───────────────────────────────────────────────────────────────────────────────────────────┐
│ SOC Card │ │ Display DC │
│ │ │ ┌──────────────────────────────┐ │
│ DSI0 │ │ │ DLC Display CONN │ │
│ ├─ DSICLK_P/M ─┼─────────┼────────────────────────────────────────────────────────┼──► DSICLK_P/M │ │
│ ├─ DSILN0_P/M ─┼─────────┼────────────────────────────────────────────────────────┼──► DSILN0_P/M │ │
│ ├─ DSILN1_P/M ─┼─────────┼────────────────────────────────────────────────────────┼──► DSILN1_P/M │ │
│ ├─ DSILN2_P/M ─┼─────────┼────────────────────────────────────────────────────────┼──► DSILN2_P/M │ │
│ └─ DSILN3_P/M ─┼─────────┼────────────────────────────────────────────────────────┼──► DSILN3_P/M │ │
│ │ │ │ │ │
│ 1.8V ──────────┼─────────┼──────────────────────────────────── vddi ──────────────┼──► vddi │ │
│ │ │ │ │ │
│ VSYS_PWR ──────┼─────────┼──────┐ │ │ │
│ │ │ │ │ │ │
│ LCD_BIAS_EN ───┼─────────┼──────┼──► ┌──────────────────┐ │ │ │
│ │ │ ├───►│ LCD BIAS DRIVER ├──── VREG_DISP_P (+5.5V)┼──► VREG_DISP_P (+5.5V) │ │
│ │ │ │ └──────────────────┘──── VREG_DISP_N (-5.5V)─┼──► VREG_DISP_N (-5.5V) │ │
│ │ │ │ │ │ │
│ LCD_BKLT_EN ───┼─────────┼──────┼──► ┌──────────────────┐ │ │ │
│ | | | │ WLED DRIVER ├──── VREG_WLED ──────────┼──► VREG_WLED │ │
│ │ │ └───►│ ├──── WLED_SIN1 ─────────┼──► WLED_SIN1 │ │
│ │ │ │ ├──── WLED_SIN2 ─────────┼──► WLED_SIN2 │ │
│ │ │ │ ◄─PWM─┤◄───────────────────────┼◄── CABC │ │
│ │ │ └──────────────────┘ │ │ │
│ MDP_VSYNC_P ───┼─────────┼────────────────────────────────────────────────────────┼──► MDP_VSYNC_P │ │
│ │ │ │ │ │
│ DISP_RST ──────┼─────────┼────────────────────────────────────────────────────────┼──► DISP_RST │ │
│ │ │ │ │ │
│ Touch ─//──────┼─────────┼────────────────────────────────────────────────────────┼──► Touch signals │ │
│ signals │ │ └──────────────────────────────┘ │
└─────────────────┘ └───────────────────────────────────────────────────────────────────────────────────────────┘
Thanks,
Arpit