[BUG] DM_VIDEO broken on imx6q

[Soeren Moch]

Hi,

unfortunately the patch [1] is only the first part to get DM_VIDEO
running properly on tbs2910 for u-boot-2020.10. With this, I get a valid
video output signal, but no actual video console output, only a blank
screen.

After some debugging, no with access to a HDMI monitor, the problem
seems to be:
imx6q has two ipu units, so DM_VIDEO creates 2 video devices. For these
two devices also memory for two framebuffers is reserved in
video-uclass, starting from gd->video_top downwards. Then vidconsole
correctly uses the first video device (ipu1), but apparently the
framebuffer from ipu2 at gd->video_bottom. So I see the empty
framebuffer from ipu1 while the console output goes to the framebuffer
memory of ipu2.

I guess there is the same problem on all imx6q devices with 2 ipu units,
while on imx6s/6dl devices with a single ipu everything works fine.
Disabling the second ipu in the tbs2910 devicetree also helps, but I
think this is not a proper solution.

What should be done about this? Only probing the first ipu/video device?
Assigning the framebuffer memory bottom-up? Using the assigned
framebuffer memory of the active video device for console output (seems
to be the correct solution, but maybe not so easy to implement)?
Something else?

Thanks,
Soeren

[1]
https://patchwork.ozlabs.org/project/uboot/patch/20200730121157.5305-1-smoch@web.de/