anholt
Improve underscan/overscan compensation
Browsing the raspberry pi forum many users are under the impression that there is a problem with underscan/overscan with vc4. This is a blocker for many people using vc4. Whilst I think some of this is unjustified I do think there is scope for improvement.
I connect my pi to a cheap tv. The legacy driver shifts the picture down and to the right so I have some picture missing. This can be fixed through the config.txt settings.
vc4 centres the picture correctly (as far as I can tell), but cuts the edges of the picture off on all 4 sides. To fix this I can do:
cvt 1280 720
# 1280x720 59.86 Hz (CVT 0.92M9) hsync: 44.77 kHz; pclk: 74.50 MHz
Modeline "1280x720_60.00" 74.50 1280 1344 1472 1664 720 723 728 748 -hsync +vsync
xrandr --newmode "1280x720_60.00" 74.50 1280 1344 1472 1664 720 723 728 748 -hsync +vsync
xrandr --addmode HDMI-1 1280x720_60.00
xrandr --output HDMI-1 --mode 1280x720_60.00
This gives a perfect picture, but obviously doesn't fix the framebuffer consoles. To do this I had expected the kernel cmdline video=HDMI-A-1:1280x720M@60 to do the same as the above code. However, it seems to make no difference apart from changing the mode. video=HDMI-A-1:1280x720M@60m just gives an out of sync message on the tv.
Am I missing an easy option to fix the framebuffer picture?
Going back to xrandr it seems many cards/devices have an underscan option. Is this something vc4 needs if that is what people are going to find by googling the problem?
