imx-drm: Color issues scanning out YUV420 frames through the overlay plane.

[Javier Martin <javiermartin@by.com.es>]

Hi,
I am using mainline kernel 4.1 and I was writing a small application 
that uses double buffering to read YUV420 frames from a file at 30fps 
and displays them using the overlay plane in the imx-drm driver.

The first issue I noticed is that the image was green so I had to apply 
the following patches to make the U and V components be scanned out 
properly:

http://lists.freedesktop.org/archives/dri-devel/2014-October/071052.html
http://lists.freedesktop.org/archives/dri-devel/2014-October/071025.html
http://lists.freedesktop.org/archives/dri-devel/2014-October/071048.html

The thing is that, even after applying the 3 patches above, colors are a 
bit strange. They seem about right but there are some artifacts, like a 
saturation effect that spoils the image. You can see some snapshots here 
to see what I am talking about:
https://imageshack.com/i/f0nAM5Xbj
https://imageshack.com/i/hl7bZMNjj
https://imageshack.com/i/eyRjURxRj

And the original video is the first one in this page:
http://media.xiph.org/video/derf/

On the other hand, colors in the primary plane using the fbdev interface 
and RGB look correct.

Has anyone seen something similar or is YUV420 working fine for you?

Regards,
Javier.