[PATCH 0/2] drm/panel: add WLED supply support

[PATCH 0/2] drm/panel: add WLED supply support

[Arpit Saini]

This is a follow-up to the applied ILI7807S panel support series.

Link: https://lore.kernel.org/all/20260701-ili7807s-v4-0-c7d76d4780a5@oss.qualcomm.com/

Some boards, such as the Qualcomm Shikra CQS EVK and Shikra CQM EVK,
drive the panel's backlight from an external WLED driver whose enable
input is wired through a supply, typically modeled as a fixed
regulator (e.g. vreg_wled).

Platforms without this hardware may omit wled-supply and
use the existing DCS or external backlight handling.

Signed-off-by: Arpit Saini <arpit.saini@oss.qualcomm.com>
---
Arpit Saini (2):
      dt-bindings: display: panel: add optional wled-supply
      drm/panel: ili7807s: Add WLED supply

 .../devicetree/bindings/display/panel/ilitek,ili7807s.yaml   | 12 ++++++++++++
 drivers/gpu/drm/panel/panel-ilitek-ili7807s.c                |  1 +
 2 files changed, 13 insertions(+)
---
base-commit: 6375e61c01e93e35ee7acd336a689ac1fae4b509
change-id: 20260929-wled-supply-series-e10b2c5d5103

Best regards,
-- 
Arpit Saini <arpit.saini@oss.qualcomm.com>

[PATCH 1/2] dt-bindings: display: panel: add optional wled-supply

[Arpit Saini]

Some boards drive the ILI7807S panel's backlight from an external
WLED driver whose enable input is wired to a GPIO, typically modeled
as a fixed regulator (e.g. vreg_wled).

Document the optional wled-supply property for the ILI7807S panel
binding. When present, the supply can be used to control the enable
input of the external WLED driver.

Platforms without an external WLED enable supply can omit this
property and continue to use the existing backlight handling.

Fixes: 447a76a99e24 ("dt-bindings: display: panel: add Ilitek ILI7807S panel controller")
Signed-off-by: Arpit Saini <arpit.saini@oss.qualcomm.com>
---
 .../devicetree/bindings/display/panel/ilitek,ili7807s.yaml   | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/Documentation/devicetree/bindings/display/panel/ilitek,ili7807s.yaml b/Documentation/devicetree/bindings/display/panel/ilitek,ili7807s.yaml
index ba8c5bbf8ffc..8d56b74a962a 100644
--- a/Documentation/devicetree/bindings/display/panel/ilitek,ili7807s.yaml
+++ b/Documentation/devicetree/bindings/display/panel/ilitek,ili7807s.yaml
@@ -34,6 +34,10 @@ properties:
     description: Negative LCD bias supply (AVEE), typically -5.5V
       (range -6.3V to -4.5V)
 
+  wled-supply:
+    description: Optional Supply for the WLED driver that provides the
+      panel backlight
+
 required:
   - compatible
   - reg
@@ -49,6 +53,13 @@ examples:
   - |
     #include <dt-bindings/gpio/gpio.h>
 
+    vreg_wled: regulator-wled {
+        compatible = "regulator-fixed";
+        regulator-name = "vreg_wled";
+        gpio = <&tlmm 91 GPIO_ACTIVE_HIGH>;
+        enable-active-high;
+    };
+
     dsi {
         #address-cells = <1>;
         #size-cells = <0>;
@@ -61,6 +72,7 @@ examples:
             vddi-supply = <&pm4125_l15>;
             avdd-supply = <&avdd>;
             avee-supply = <&avee>;
+            wled-supply = <&vreg_wled>;
 
             port {
                 panel_in: endpoint {

-- 
2.34.1

[PATCH 2/2] drm/panel: ili7807s: Add WLED supply

[Arpit Saini]

Some boards drive the panel's backlight from an external WLED driver
whose enable input is wired through a supply, typically modeled as a
fixed regulator (e.g. vreg_wled).

Add the WLED supply to the panel's bulk regulator list so it can be
enabled/disabled along with the other panel supplies.

Fixes: dd7ec83f4567 ("drm/panel: add Ilitek ILI7807S panel driver")
Signed-off-by: Arpit Saini <arpit.saini@oss.qualcomm.com>
---
 drivers/gpu/drm/panel/panel-ilitek-ili7807s.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/gpu/drm/panel/panel-ilitek-ili7807s.c b/drivers/gpu/drm/panel/panel-ilitek-ili7807s.c
index 12b491b0bca4..eba74f2677ed 100644
--- a/drivers/gpu/drm/panel/panel-ilitek-ili7807s.c
+++ b/drivers/gpu/drm/panel/panel-ilitek-ili7807s.c
@@ -38,6 +38,7 @@ static const struct regulator_bulk_data ili7807s_supplies[] = {
 	{ .supply = "vddi" },
 	{ .supply = "avdd" },
 	{ .supply = "avee" },
+	{ .supply = "wled" },
 };
 
 static inline struct ili7807s *to_ili7807s(struct drm_panel *panel)

-- 
2.34.1

Re: [PATCH 1/2] dt-bindings: display: panel: add optional wled-supply

[Krzysztof Kozlowski]

On Tue, Sep 29, 2026 at 06:42:20PM +0530, Arpit Saini wrote:
> Some boards drive the ILI7807S panel's backlight from an external
> WLED driver whose enable input is wired to a GPIO, typically modeled
> as a fixed regulator (e.g. vreg_wled).

You describe something else. What's fixed regulator should not matter
here. Which pin is it in ILI7807S?

It seems you just want to represent GPIO with a regulator. This is just
confusing and typical downstream workaround.

> 
> Document the optional wled-supply property for the ILI7807S panel
> binding. When present, the supply can be used to control the enable
> input of the external WLED driver.
> 
> Platforms without an external WLED enable supply can omit this
> property and continue to use the existing backlight handling.
> 
> Fixes: 447a76a99e24 ("dt-bindings: display: panel: add Ilitek ILI7807S panel controller")
> Signed-off-by: Arpit Saini <arpit.saini@oss.qualcomm.com>
> ---
>  .../devicetree/bindings/display/panel/ilitek,ili7807s.yaml   | 12 ++++++++++++
>  1 file changed, 12 insertions(+)
> 
> diff --git a/Documentation/devicetree/bindings/display/panel/ilitek,ili7807s.yaml b/Documentation/devicetree/bindings/display/panel/ilitek,ili7807s.yaml
> index ba8c5bbf8ffc..8d56b74a962a 100644
> --- a/Documentation/devicetree/bindings/display/panel/ilitek,ili7807s.yaml
> +++ b/Documentation/devicetree/bindings/display/panel/ilitek,ili7807s.yaml
> @@ -34,6 +34,10 @@ properties:
>      description: Negative LCD bias supply (AVEE), typically -5.5V
>        (range -6.3V to -4.5V)
>  
> +  wled-supply:
> +    description: Optional Supply for the WLED driver that provides the
> +      panel backlight
> +
>  required:
>    - compatible
>    - reg
> @@ -49,6 +53,13 @@ examples:
>    - |
>      #include <dt-bindings/gpio/gpio.h>
>  
> +    vreg_wled: regulator-wled {
> +        compatible = "regulator-fixed";
> +        regulator-name = "vreg_wled";
> +        gpio = <&tlmm 91 GPIO_ACTIVE_HIGH>;
> +        enable-active-high;
> +    };

Irrelevant here

Best regards,
Krzysztof

Re: [PATCH 1/2] dt-bindings: display: panel: add optional wled-supply

[Krzysztof Kozlowski]

On 01/10/2026 08:55, Krzysztof Kozlowski wrote:
> On Tue, Sep 29, 2026 at 06:42:20PM +0530, Arpit Saini wrote:
>> Some boards drive the ILI7807S panel's backlight from an external
>> WLED driver whose enable input is wired to a GPIO, typically modeled
>> as a fixed regulator (e.g. vreg_wled).
> 
> You describe something else. What's fixed regulator should not matter
> here. Which pin is it in ILI7807S?
> 
> It seems you just want to represent GPIO with a regulator. This is just
> confusing and typical downstream workaround.

What's more, you basically REVERT the review YOU RECEIVED in v1. Really,
just sneak the same stuff 3 months after like the review never happened.

NAK

Best regards,
Krzysztof

Re: [PATCH 2/2] drm/panel: ili7807s: Add WLED supply

[Krzysztof Kozlowski]

On 29/09/2026 15:12, Arpit Saini wrote:
> Some boards drive the panel's backlight from an external WLED driver
> whose enable input is wired through a supply, typically modeled as a
> fixed regulator (e.g. vreg_wled).
> 
> Add the WLED supply to the panel's bulk regulator list so it can be
> enabled/disabled along with the other panel supplies.
> 
> Fixes: dd7ec83f4567 ("drm/panel: add Ilitek ILI7807S panel driver")

Not a fix. Read review you already received four months ago.

Best regards,
Krzysztof

Re: [PATCH 1/2] dt-bindings: display: panel: add optional wled-supply

[Dmitry Baryshkov]

On Thu, Oct 01, 2026 at 08:57:52AM +0200, Krzysztof Kozlowski wrote:
> On 01/10/2026 08:55, Krzysztof Kozlowski wrote:
> > On Tue, Sep 29, 2026 at 06:42:20PM +0530, Arpit Saini wrote:
> >> Some boards drive the ILI7807S panel's backlight from an external
> >> WLED driver whose enable input is wired to a GPIO, typically modeled
> >> as a fixed regulator (e.g. vreg_wled).
> > 
> > You describe something else. What's fixed regulator should not matter
> > here. Which pin is it in ILI7807S?
> > 
> > It seems you just want to represent GPIO with a regulator. This is just
> > confusing and typical downstream workaround.
> 
> What's more, you basically REVERT the review YOU RECEIVED in v1. Really,
> just sneak the same stuff 3 months after like the review never happened.
> 
> NAK

After discussing this offline with Krzysztof. It's not a supply (my
fault), it's an LCD driver. So, the best way to handle your displaycard
seems to add a gpio-backlight, reference it from the panel and then in
the driver check for the backlight's max_brightness level. If it's 1,
then you have to send extra DCS commands to control PWM. If it's
higher, use normal backlight class controls.

-- 
With best wishes
Dmitry

Re: [PATCH 1/2] dt-bindings: display: panel: add optional wled-supply

[Arpit Saini]

On 10/1/2026 3:25 PM, Dmitry Baryshkov wrote:
> On Thu, Oct 01, 2026 at 08:57:52AM +0200, Krzysztof Kozlowski wrote:
>> On 01/10/2026 08:55, Krzysztof Kozlowski wrote:
>>> On Tue, Sep 29, 2026 at 06:42:20PM +0530, Arpit Saini wrote:
>>>> Some boards drive the ILI7807S panel's backlight from an external
>>>> WLED driver whose enable input is wired to a GPIO, typically modeled
>>>> as a fixed regulator (e.g. vreg_wled).
>>>
>>> You describe something else. What's fixed regulator should not matter
>>> here. Which pin is it in ILI7807S?
>>>
>>> It seems you just want to represent GPIO with a regulator. This is just
>>> confusing and typical downstream workaround.
>>
>> What's more, you basically REVERT the review YOU RECEIVED in v1. Really,
>> just sneak the same stuff 3 months after like the review never happened.
>>
>> NAK
> 
> After discussing this offline with Krzysztof. It's not a supply (my
> fault), it's an LCD driver. So, the best way to handle your displaycard
> seems to add a gpio-backlight, reference it from the panel and then in
> the driver check for the backlight's max_brightness level. If it's 1,
> then you have to send extra DCS commands to control PWM. If it's
> higher, use normal backlight class controls.
> 

Hi Dmitry, Krzysztof 

I have a few clarifying questions regarding the proposed approach. Please let me know if I've misunderstood anything.
 
  panel_backlight: backlight {
      compatible = "gpio-backlight";
      gpios = <&tlmm 91 GPIO_ACTIVE_HIGH>;
      default-on;
  };

1) Adding gpio-backlight and check for max_brightness level if its 1,

   If we model LCD_BKLT_EN using gpio-backlight, the backlight device effectively exposes only on/off control (max_brightness = 1), 
   we can't support the full range of brightness i.e 0 to 16383 (0x3FFF) 

2) Adding gpio-backlight and based upon max_brightness level of 1 , are you suggesting to register another 
   backlight device that can actually drive DCS brightness. In that case we can actually have the MIPI DCS controlled brightness 

   If so, wouldn't that result in two backlight devices associated with the same panel:

    gpio-backlight device for enable/disable
    panel backlight device for DCS brightness control
 
   Is that the expected design?

3) I previously tried modeling LCD_BKLT_EN using pinctrl states (panel_bl_en / panel_bl_suspend) 
   for the enable GPIO itself. However, Dmitry suggested modeling it as a regulator instead:

   Link : https://lore.kernel.org/all/qkhgg5x67sijiialucvzac275zhpjrtt47a4udjpyzmgvilut5@dcrslq3ai7mc/

4) Modeled optional regulator wled-supply: a regulator that only gates the external backlight driver chip's power/enable, 
   with DCS remaining the sole brightness path in this current patch , the panel-himax-hx83121a.c does exactly the same.
   
   Would this can be the preferred modeling for such panels?

Please refer to this Hardware diagram I explained earlier , 
Link : https://lore.kernel.org/all/bade420c-aeb8-4bdd-b0cf-3ade17b21c18@oss.qualcomm.com/


Please let me know your suggestions.

Thanks,
Arpit


   

  

Re: [PATCH 1/2] dt-bindings: display: panel: add optional wled-supply

[Neil Armstrong]

On 10/1/26 20:09, Arpit Saini wrote:
> 
> 
> On 10/1/2026 3:25 PM, Dmitry Baryshkov wrote:
>> On Thu, Oct 01, 2026 at 08:57:52AM +0200, Krzysztof Kozlowski wrote:
>>> On 01/10/2026 08:55, Krzysztof Kozlowski wrote:
>>>> On Tue, Sep 29, 2026 at 06:42:20PM +0530, Arpit Saini wrote:
>>>>> Some boards drive the ILI7807S panel's backlight from an external
>>>>> WLED driver whose enable input is wired to a GPIO, typically modeled
>>>>> as a fixed regulator (e.g. vreg_wled).
>>>>
>>>> You describe something else. What's fixed regulator should not matter
>>>> here. Which pin is it in ILI7807S?
>>>>
>>>> It seems you just want to represent GPIO with a regulator. This is just
>>>> confusing and typical downstream workaround.
>>>
>>> What's more, you basically REVERT the review YOU RECEIVED in v1. Really,
>>> just sneak the same stuff 3 months after like the review never happened.
>>>
>>> NAK
>>
>> After discussing this offline with Krzysztof. It's not a supply (my
>> fault), it's an LCD driver. So, the best way to handle your displaycard
>> seems to add a gpio-backlight, reference it from the panel and then in
>> the driver check for the backlight's max_brightness level. If it's 1,
>> then you have to send extra DCS commands to control PWM. If it's
>> higher, use normal backlight class controls.
>>
> 
> Hi Dmitry, Krzysztof
> 
> I have a few clarifying questions regarding the proposed approach. Please let me know if I've misunderstood anything.
>   
>    panel_backlight: backlight {
>        compatible = "gpio-backlight";
>        gpios = <&tlmm 91 GPIO_ACTIVE_HIGH>;
>        default-on;
>    };
> 
> 1) Adding gpio-backlight and check for max_brightness level if its 1,
> 
>     If we model LCD_BKLT_EN using gpio-backlight, the backlight device effectively exposes only on/off control (max_brightness = 1),
>     we can't support the full range of brightness i.e 0 to 16383 (0x3FFF)
> 
> 2) Adding gpio-backlight and based upon max_brightness level of 1 , are you suggesting to register another
>     backlight device that can actually drive DCS brightness. In that case we can actually have the MIPI DCS controlled brightness
> 
>     If so, wouldn't that result in two backlight devices associated with the same panel:
> 
>      gpio-backlight device for enable/disable
>      panel backlight device for DCS brightness control
>   
>     Is that the expected design?

It's a great question because there's a large variety of how backlight is
implemented, and some panels can drive a PWM to an actually backlight controller
which uses external pwm. In this case we should model the backlight IC as
backlight driver with only 1 or 0 capability and use the DCS to program
the PWM.

So it leads exactly to your issue. So perhaps one way would be to either:
- call into the gpio-backlight from the DCS callback, we may need to fix some locking issues
- add way to "link" backlight devices so the backlight value can be propagated


In any case the problem remains that both backlight devices will be exposed
to userspace, which we don't want. So additional changes will be needed.

> 
> 3) I previously tried modeling LCD_BKLT_EN using pinctrl states (panel_bl_en / panel_bl_suspend)
>     for the enable GPIO itself. However, Dmitry suggested modeling it as a regulator instead:
> 
>     Link : https://lore.kernel.org/all/qkhgg5x67sijiialucvzac275zhpjrtt47a4udjpyzmgvilut5@dcrslq3ai7mc/
> 
> 4) Modeled optional regulator wled-supply: a regulator that only gates the external backlight driver chip's power/enable,
>     with DCS remaining the sole brightness path in this current patch , the panel-himax-hx83121a.c does exactly the same.
>     
>     Would this can be the preferred modeling for such panels?
> 
> Please refer to this Hardware diagram I explained earlier ,
> Link : https://lore.kernel.org/all/bade420c-aeb8-4bdd-b0cf-3ade17b21c18@oss.qualcomm.com/
> 
> 
> Please let me know your suggestions.
> 
> Thanks,
> Arpit
> 
> 
>     
> 
>