pwm_bl add framebuffer from fbcon

[Christian N]

Hi All

First at all I introduce my usecase
-My board based on ARM (OMPA4) can get a custom splash screen on booting
using fbcon.
-By Device Tree I can configure screen backlight with desired level.

i'm trying to turn on backlight when splash screen is displayed and not
before to avoid "white flashes".

I read
Documentation/devicetree/bindings/pwm/pwm.txt
Documentation/devicetree/bindings/leds/pwm-backlight.txt
Documentation/fb/...
https://www.kernel.org/doc/html/v4.14/admin-guide/kernel-parameters.html

Also I noticed that pwm_bl has pwm_backlight_check_fb operation, but I
didnt find a clear way to relate frame buffer used by fbcon with pwm_bl
related functions or how to customize by DT or kernel config which frame
buffer should be used by pwm_bl to turn on when valid data is ready in fb

Any hints will be apreciated.

Regards