[Bug 94921] New: Remove illogical/bogus "Automatic" mode from "Broadcast RGB" property

[bugzilla-daemon at bugzilla.kernel.org]

https://bugzilla.kernel.org/show_bug.cgi?id=94921

            Bug ID: 94921
           Summary: Remove illogical/bogus "Automatic" mode from
                    "Broadcast RGB" property
           Product: Drivers
           Version: 2.5
    Kernel Version: git
          Hardware: All
                OS: Linux
              Tree: Mainline
            Status: NEW
          Severity: normal
          Priority: P1
         Component: Video(DRI - Intel)
          Assignee: intel-gfx-bugs at lists.freedesktop.org
          Reporter: tom.ty89 at gmail.com
                CC: intel-gfx-bugs at lists.freedesktop.org
        Regression: No

Because of this patch, which was added quite sometime ago, some/many HDMI/DP
users might experience weathered/greyish color if they don't manually set the
"Broadcast RGB" property (aka Color Range, etc.) to "Full" through xrandr:
http://lists.freedesktop.org/archives/dri-devel/2013-January/033576.html

Many user or devs might not even know or aware that, this "Automatic" mechanism
simply decide what range you should use according to the display "mode" (i.e.
resolution + refresh rate, see Ref. 1).

Actually it's quite obvious if you read a bit of the code in the patch. Yet
some users or even devs claim that it's due to the "broken EDID of your
monitor" (while EDID actually has no bit at all to indicate what color range a
monitor can support, but only color space, see Ref. 2), or some other reasons
come from nowhere.

So basically there COULD NOT BE ANY REAL "Automatic" mechanism, because what a
real "Automatic" would do is sending the type of signal that the monitor can
handle.

AFAIK, no monitors is produced according the the CEA or DP guidelines as quoted
in the patch. I even doubt if those guidelines are supposed to be conformed by
monitor manufacturers or drivers devs at all. 1920x1080 monitors takes Limited
Range and 2560x1440 monitors takes Full Range? Seriously?

So which one should be the default? Full or Limited? In my opinion, Full should
at least be the default of DisplayPort, while Limited might be fine as the
default of HDMI.

First, we can assume all AV consumer products output Limited Range and possibly
limited range only (See Ref. 4 and 5), which would mostly (the modern ones)
have HDMI. IMO if any manufacturers made a monitor with HDMI port, it's
reasonable to expect that it supports Limited Range or both. On the other hand,
DisplayPort are mostly seen on PC monitors only but almost never on TVs or so,
and traditionally PC monitors are NOT supposed to support Limited Range, aka TV
Level.

Second, I don't see Limited Range applies on anything but video
playback/encoding. It is kind of lossy for gaming/photo editing/web browsing,
etc. unless his monitors doesn't support full range anyway.

Nevertheless, I'll say it's totally fine to use Full Range, the "PC Level", as
default for both ports.

References:
1. Which modes might "weather" your monitor:
http://en.wikipedia.org/wiki/Extended_display_identification_data#EDID_1.3_data_format
2. About what EDID can tell, also pay attention to Bytes 24, Bit 4-3:
http://en.wikipedia.org/wiki/Extended_display_identification_data#EDID_1.3_data_format
3. A hilarious line found in the source:
https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/drivers/gpu/drm/drm_edid.c#n606
4. http://en.wikipedia.org/wiki/Rec._601#Signal_format
5. http://en.wikipedia.org/wiki/Rec._709#Digital_representation

P.S. One might think that perhaps a monitor support any of the YCbCr color
space would support Limited Range as well. But even if so, the range would
still be inferior to the Full one for non-video use cases mentioned above.

-- 
You are receiving this mail because:
You are on the CC list for the bug.
You are the assignee for the bug.