Re: [PATCH v8 2/7] arm64: dts: imx8mm: imx8mp: Add LVDS DTOs for Data Modul i.MX8M Mini and Plus eDM SBC

On 7/31/26 6:36 PM, Frank Li wrote:

Hello Frank,

>> [Severity: Medium]
>> Will this hardcoded adapter-specific backlight enable pin break the backlight
>> on the i.MX8MP native LVDS adapter?
>>
>> By setting enable-gpios = <&gpio3 0 GPIO_ACTIVE_HIGH>; in
>> imx8mm-data-modul-edm-sbc-overlay-lvds-g215hvn011.dtsi, the adapter-specific
>> gpio3 0 pin configuration leaks into the generic panel configuration.
>>
>> Because the native adapter overlay
>> (imx8mp-data-modul-edm-sbc-overlay-edm-sbc-imx8mp-lvds-g215hvn011.dtso)
>> includes this generic panel file but fails to override enable-gpios
>> (to <&gpiowifi 0 GPIO_ACTIVE_HIGH>) and remove pinctrl-0, the native adapter
>> inherits the incorrect gpio3 0 pin, which may leave the backlight off.
> 
> 
> This finial dtb
> 
> backlight {
>                  power-supply = <0x120>;
>                  pwm-off-delay-ms = <0x0a>;
>                  post-pwm-on-delay-ms = <0x0a>;
>                  enable-gpios = <0x54 0x00 0x00>;
> 		^^^
>                  pinctrl-0 = <0xbc>;
>                  pinctrl-names = "default";
>                  compatible = "pwm-backlight";
>                  brightness-levels = <0x00 0x01 0x0a 0x14 0x1e 0x28 0x32 0x3c 0x46 0x4b 0x50 0x5a 0x64>;
>                  default-brightness-level = <0x07>;
>                  pwms = <0x9e 0x00 0x1046a 0x00>;
>                  status = "okay";
>                  phandle = <0xa1>;
>          };
> 
> At drivers/video/backlight/pwm_bl.c
> 
> get optional gpio "enable-gpios", which toggle this gpio
>   <&gpiowifi 0 GPIO_ACTIVE_HIGH>, which may not impact function, but it
> is potentially impact other funciton, if there pin conflict, need disable
> related module.

This is OK, this panel backlight supply comes from the base board in 
either case.

>>> diff --git a/arch/arm64/boot/dts/freescale/imx8mp-data-modul-edm-sbc-overlay-edm-sbc-imx8mp-lvds.dtsi b/arch/arm64/boot/dts/freescale/imx8mp-data-modul-edm-sbc-overlay-edm-sbc-imx8mp-lvds.dtsi
>>> new file mode 100644
>>> index 0000000000000..b06af369a9245
>>> --- /dev/null
>>> +++ b/arch/arm64/boot/dts/freescale/imx8mp-data-modul-edm-sbc-overlay-edm-sbc-imx8mp-lvds.dtsi
>>> @@ -0,0 +1,79 @@
>> [ ... ]
>>> +	reg_panel_bl_supply: regulator-panel-bl-supply {
>> [ ... ]
>>> +		/*
>>> +		 * MP2328 voltage divider settings:
>>> +		 *   R1=51k1
>>> +		 *   R2=5k62 with optional series Rs=2k21 (12V)
>>> +		 *
>>> +		 * 1 / Rx = (1 / R2) [ + (1 / Rs)][ + (1 / Rt)]
>>> +		 * Vout = 0.5 + ((R1 / Rx) * 0.5)
>>> +		 */
>>
>> [Severity: Low]
>> Is this mathematical formula for the MP2328 correct?
>>
>> For the 12V backlight supply, calculating Rx in parallel (1/Rx = 1/R2 + 1/Rs)
>> using R1=51.1k, R2=5.62k, and Rs=2.21k yields Rx=1.586k.
> 
> I calc it,   1/(1/5.62 + 1/2.21) = 1.586
> 
>>
>> Applying that to Vout = 0.5 + ((51.1k / 1.586k) * 0.5) gives approximately
>> 16.6V, not 12V.
> 
> It is correct, it is 16.6v.
> 
> According to gpios settings,
> 
> GPIO 0 1 to choose coonnect R2 and Rs
> 
> only choose Rs, it is 12v
> only choose R2, it is 5v.
> 
> Not sure how to generate 3.3v and 40v,
It's the comment that is wrong, the resistors in schematic are these:

-        *   R2=9k09 with optional series Rs=5k62 (5V) or Rt=2k21 (12V)
+        *   R2=9k09 with optional series Rs=14k7 (5V) or Rt=2k94 (12V)

The regulator configuration in DT is correct. I'll fix that in V9.

Is there anything else that I should address before sending V9 ?

Thank you.