Re: [PATCH v4 2/4] drm: mxsfb: Add optional DPI output bus-width configuration

[Luca Ceresoli]

Hi Francesco,

> LCDIF programs LCD_DATABUS_WIDTH from the selected media bus format. The
> format reported by the downstream panel or bridge describes the display
> input, but it does not describe how the LCDIF data pins are physically
> wired on the board.
>
> These can differ. For example, a 16-bit LCDIF bus can be connected to a
> 24-bit display by wiring the available color bits to the corresponding
> display inputs. In that case, using the display's 24-bit format to
> configure LCDIF selects the wrong data-bus mode and changes the assignment
> of color bits on the LCD_DATA pins.
>
> Read the optional bus-width endpoint property from the LCDIF output port
> and use it to select the media bus format used to configure LCDIF. This
> allows the LCDIF bus mode to describe the physical interface
> independently of the downstream display format.
>
> When the optional property is absent, or it has an invalid value, continue
> using the format reported by the downstream display device, preserving
> the existing behavior. The code is not validating the DT for
> correctness and just fall back to the previous behavior in case of
> errors.

Why? Generally speaking errors are better spotted immediately, not ignored
silently.

Otherwise looks good. I also tested on i.MX8MP with no regressions.

Luca

-- 
Luca Ceresoli, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com