Re: [PATCH 0/3] drm/mxsfb: support swapped RGB lanes

[Sam Ravnborg <sam@ravnborg.org>]

Hi Ahmad.

On Wed, Jan 02, 2019 at 10:05:31PM +0100, Stefan Agner wrote:
> On 02.01.2019 18:02, Ahmad Fatoum wrote:
> > Hello,
> > 
> > I got a board with the RED[0:7]/BLUE[0:7] lanes originating from the
> > LCDIF swapped and would like to describe this in the device tree:
> > 
> > This first patch extends the mxsfb driver to support
> > following bus formats:
> > 	MEDIA_BUS_FMT_BGR888_1X24
> > 	MEDIA_BUS_FMT_RBG888_1X24
> > 	MEDIA_BUS_FMT_GBR888_1X24
> > 
> > The latter two patches add a new interface-pix-fmt property
> > (named so because fsl,imx-parallel-display has one),
> > which allows a device tree to override the bus format to account
> > for swapped signal lanes.
> > 
> > Thoughts?
I have not seen the original mail, so a reply to this mail.
The problem with the RED/BLUE lines swapped is something I
have encountered while working with DRM support for Atmel at91sam9263 too.

The solution selected is to extend the endpoint with
a new optional property:

- wiring: Wiring of data lines to display.
  "straight" - normal wiring.
  "red-blue-reversed" - red and blue lines reversed.

(media/video-interfaces.txt)


The DT node looks like this:

               port@0 {
                        reg = <0>;
                        #address-cells = <1>;
                        #size-cells = <0>;
                        lcdc_panel_output: endpoint@0 {
                                reg = <0>;
                                wiring = "red-blue-reversed";
                                remote-endpoint = <&panel_input>;
                        };
                };

This allows us to specify the swapping in the endpoint and
not in the panel.
So we can use the same panel, with the same bus_format, in several
designs some with red-blue swapped (reversed), and some not.

This above is inspired by some earlier thread on dri-devel.
I recall Peter Rosin was one of the main source of inspiration.

Patches I refer to are not yet posted, this is work-in-progess.
They need more polishing and testing before they are dri-devel ready.

	Sam
_______________________________________________
dri-devel mailing list
dri-devel@lists.freedesktop.org
https://lists.freedesktop.org/mailman/listinfo/dri-devel