[Intel-gfx] HDMI colour space and depth questions (YCbCr, xvYCC, Deep Colour)

Jesse Barnes jbarnes at virtuousgeek.org
Tue Feb 28 18:59:00 CET 2012

On Tue, 28 Feb 2012 13:53:20 +0000
Paul Owen <paul at starstreak.net> wrote:
> Okay so back to this question of broadcast rgb/limited/full range
> colour. I'm not so sure it is working at all under Sandybridge. I use
> XBMC under Linux (Ubuntu) and do not see any difference in the picture
> when I do either of the following:
> 1) Set BROADCAST_RGB = 1 (or 0) in the xorg.conf - in fact the X log
> shows the setting is ignored seemingly wherever I put it
> 2) type on the command line, xrandr -d :0 --output <OUTPUT HERE> --set
> "Broadcast RGB" "Limited 16:235"
> and:
> 3) type on the command line, xrandr -d :0 --output <OUTPUT HERE> --set
> "BROADCAST_RGB" 1 - this just errors as previously noted here and in
> other related topics

There are several places we need to set extended vs normal range:
DSP*CNTR (bit 25)
PIPE*CONF (bits 26 and 13)
TRANS*CONF (bit 10, for xvYCC DP configs)
DVS*CNTR (for sprites, bit 21)

I assume you're on HDMI and not using sprites, so can you confirm the
DSP*CNTR and PIPE*CONF bits with intel_reg_read?  You can try setting
the range bits by hand with intel_reg_write, but that might not work
(you may need a full pipe shutdown and restart to change them, in which
case you'd need to hack intel_display.c to do it for you).

> It seems to me it outputs full range colour regardless of this setting
> - are the above methods "potentially" correct? As such it limits the
> usefulness of the platform to htpc users - under Linux that is. Under
> Windows it seems to automatically detect that a TV is connected and
> switch to 16-235 (using EDID info and manufacturer data maybe?). Is it
> at all possible to manage this under Linux in a similar way maybe, any
> future plans perhaps? This is, aside from the fractional framerate
> issue probably the last major issue limiting the platform under Linux
> and in my case XBMC.

Yeah defaulting to the limited range for TVs may make sense.  Paulo has
been looking at TV detection and HDMI infoframes a bit, so may be able
to whip up a patch.

We probably just have a bug here and don't set all the bits we need

Jesse Barnes, Intel Open Source Technology Center
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