PWM for backlight control of display on Windows On Arm (i.MX8M)

[Norihiro]

Hello, 

We want to control the backlight for external display from Windows On Arm running on our custom i.MX8M board.

Here is our understanding about software that are involved in the backlight control below.

-ACPI gives us standard method to adjust the backlight.

-Laptop PC often uses ACPI to control the backlight.

-Backlight is controled by sending a command from Windows to UEFI. 

-Windows must have a driver and configuration to control the backlight.

Here is our questions about the backlight control on running Windows On Arm on i.MX8M.

(1) We see the following control flow in the document of uefi. 

Which is correct understanding about control flow from Windows to the actual hardware(i.MX8M)?

a) Calling a driver directly? (Backlight driver is needed?)

b) Backlight is controlled via ACPI?

c) Both a) and b)  works toghether?

(2) If we trun off or on the external display from Windows, Which is correct understanding about control flow?

a) Calling a display driver directly to turn off or on the external display?

b) It is controlled via ACPI?

c) Both a) and b)  works toghether?

(3) We need to control the backlight along with turning off or on the external display.

It means that a fucntion for turning on and off the backlight must be integrated in the display driver.

In this case, driver uses the method in above question (1) to change the luminance?

Regards,

Norihiro Michigami

[Norihiro · Accepted solution]

Hello Hector, 

Thank you for your reply.  I understood NXP couldn't help us on this topic at this mement. 

We will try to find out 3rd party who could suggest our questions.

Regards,

Norihiro Michigami

AVNET

[jakub_zigacek]

Hello @Norihiro,

can you please give more details on for what display interface do you want to set brightness? We are currently working on basic enablement of this feature. So far we are able to control PWM output for LVDS interface on i.MX8MP from Display setting in Windows.

Best Regards, Jakub

[george]

Hello @jakub_zigacek,

@Norihiro  is my boss. I am contacting you on his behalf

The PWM output we want to control from the Windows system is GPIO1_IO11.

But it seems you already have the solution.

Please provide a patch or modification for the BSP.

Thanks,
George

[jakub_zigacek]

Hello @george,

please use the attached patch. It is created over BSP-1.5.1, which should be release within weeks. But changes should be in sources that are same or similar as are in 1.5.0.

Best Regards, Jakub

[george]

Hello @jakub_zigacek,

Thank you for your wonderful support.

By simply replacing the newly generated firmware_uuu.bin and Galcore driver by your patch, We can control the PWM output between 0% and 99% using the Windows system slide bar.

Thanks,
George

[george]

Hello @jakub_zigacek,

Your help is appreciated, that's great.
I'll tell my customers to try it.

Thanks,
George

[hector_delgado]

Hi @Norihiro ,

I hope you're doing well!

Our current scope of support doesn't include custom boards at the moment, so there's very limited help we could provide, specially regarding backlight drivers/software. I apologize for any inconvenience this may cause. Thank you.

Best regards,
Hector.