Video overlay on sabresd

[Nikolay Dimitrov <picmaster@mail.bg>]

Hi guys,

I'm trying to get the video overlay working on imx6q sabresd's HDMI.
Here's the kernel command line:

console=ttymxc0,115200 root=/dev/mmcblk2p2 rootwait rw 
video=mxcfb0:dev=hdmi,1280x720M@60,if=RGB2
4,bpp=32 fbmem=28M

This is the kernel version:

# uname -a
Linux imx6qsabresd 3.14.28-1.0.0_ga+g91cf351 #1 SMP PREEMPT Tue May 19 
17:32:51 EEST 2015 armv7l
GNU/Linux

Here are the framebuffer devices nodes:

# ls -lh /dev/fb*
crw-rw----    1 root     video      29,   0 Jan  1  1970 /dev/fb0
crw-rw----    1 root     video      29,   1 Jan  1  1970 /dev/fb1
crw-rw----    1 root     video      29,   2 Jan  1  1970 /dev/fb2
crw-rw----    1 root     video      29,   3 Jan  1  1970 /dev/fb3

I can write arbitrary data on /dev/fb0 and see it on screen, like this:

# cat /bin/busybox.nosuid > /dev/fb0

But I can't write to /dev/fb1:

# cat /bin/busybox.nosuid > /dev/fb1
cat: write error: No space left on device

I'm assuming that fb0 is the background layer, and fb1 is the
foreground IPU layer.

So the question is - how to make the foreground (fb1) layer working at
all? Should I configure mxcfb1 in the bootargs, or it needs some IOCTL
in /dev/fb1 to enable the device?

Thanks in advance. Regards,
Nikolay