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

[bugzilla-daemon at bugzilla.kernel.org]

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

--- Comment #1 from Tom Yan <tom.ty89 at gmail.com> ---
Allow me to further explain a bit about what I think.

First of all, any PC (or any source device that does not only/mainly serve as a
video playback device) should not conform the cea(/hdmi/dp) guidelines in the
current "automagical" way. The driver should only conform them in the way of
giving capabilities for the users to switch the color range and color space
ACCORDING TO THEIR OWN NEEDS/USE CASES and the capability of their monitor. The
mechanism might be rational for products like DVD/Blu-ray players since the
source they deal with is mostly encoded in YCbCr/limited range, but it's
totally not the case for PCs.

As what I have mentioned in the last post script, we can assume that monitors
which support YCbCr color space would support limited range since full range is
not allowed for YCbCr in both HDMI/DP specs (See Refs.), or inheritly. Hence
what color space a monitor supports could imply its capabilitiy on color range.

So if you insists that the driver should conform the cea guideline in the
current way, it should only conform when the EDID indicates that the monitor
support YCbCr. In other case, the driver COULD NOT have determined its
capabilities on color range, and hence SHOULD NOT conform the guidelines NO
MATTER WHAT.

References (Freely available after filling out a form, kind of outdated
though):
http://www.hdmi.org/manufacturer/specification.aspx Table 6-3
http://www.vesa.org/vesa-standards/free-standards/ Table 5-1

P.S. I withdraw the idea that limited range can be used as default for HDMI. I
mentioned the idea only because it's more likely for a monitor with HDMI to
support YCbCr and hence limited range than a monitor with only other ports. Yet
according to the specs above, it is not a must unless it has another port with
existing capabilities of supporting YCbCr or similar. See Section 6.2.3 in the
HDMI spec and Table 5-1 in the DP spec.

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