On Fri, Mar 17, 2023 at 06:40:53PM +0100, Sebastian Wick wrote: > On Fri, Mar 17, 2023 at 5:34 PM Ville Syrjälä > <ville.syrjala@xxxxxxxxxxxxxxx> wrote: > > > > On Fri, Mar 17, 2023 at 05:37:51PM +0200, Pekka Paalanen wrote: > > > On Fri, 17 Mar 2023 16:14:38 +0200 > > > Ville Syrjälä <ville.syrjala@xxxxxxxxxxxxxxx> wrote: > > > > > > > On Fri, Mar 17, 2023 at 03:35:53PM +0200, Pekka Paalanen wrote: > > > > > On Fri, 17 Mar 2023 14:50:40 +0200 > > > > > Ville Syrjälä <ville.syrjala@xxxxxxxxxxxxxxx> wrote: > > > > > > > > > > > On Fri, Mar 17, 2023 at 10:53:35AM +0200, Pekka Paalanen wrote: > > > > > > > On Fri, 17 Mar 2023 01:01:38 +0200 > > > > > > > Ville Syrjälä <ville.syrjala@xxxxxxxxxxxxxxx> wrote: > > > > > > > > > > > > > > > On Thu, Mar 16, 2023 at 10:13:54PM +0100, Sebastian Wick wrote: > > > > > > > > > On Thu, Mar 16, 2023 at 1:35 PM Ville Syrjälä > > > > > > > > > <ville.syrjala@xxxxxxxxxxxxxxx> wrote: > > > > > > > > > > > > > > > > > > > > On Thu, Mar 16, 2023 at 01:34:49PM +0200, Pekka Paalanen wrote: > > > > > > > > > > > On Thu, 16 Mar 2023 12:47:51 +0200 > > > > > > > > > > > Ville Syrjälä <ville.syrjala@xxxxxxxxxxxxxxx> wrote: > > > > > > > > > > > > > > > > > > > > > > > On Thu, Mar 16, 2023 at 12:07:01PM +0200, Pekka Paalanen wrote: > > > > > > > > > > > > > On Thu, 16 Mar 2023 11:50:27 +0200 > > > > > > > > > > > > > Ville Syrjälä <ville.syrjala@xxxxxxxxxxxxxxx> wrote: > > > > > > > > > > > > > > > > > > > > > > > > > > > On Thu, Mar 16, 2023 at 01:37:24AM +0100, Sebastian Wick wrote: > > > > > > > > > > > > > > > On Tue, Mar 7, 2023 at 4:12 PM Harry Wentland <harry.wentland@xxxxxxx> wrote: > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > We want compositors to be able to set the output > > > > > > > > > > > > > > > > colorspace on DP and HDMI outputs, based on the > > > > > > > > > > > > > > > > caps reported from the receiver via EDID. > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > About that... The documentation says that user space has to check the > > > > > > > > > > > > > > > EDID for what the sink actually supports. So whatever is in > > > > > > > > > > > > > > > supported_colorspaces is just what the driver/hardware is able to set > > > > > > > > > > > > > > > but doesn't actually indicate that the sink supports it. > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > So the only way to enable bt2020 is by checking if the sink supports > > > > > > > > > > > > > > > both RGB and YUV variants because both could be used by the driver. > > > > > > > > > > > > > > > Not great at all. Something to remember for the new property. > > > > > > > > > > > > > > > > > > > > > > > > > > > > Hmm. I wonder if that's even legal... Looks like maybe it > > > > > > > > > > > > > > is since I can't immediately spot anything in CTA-861 to > > > > > > > > > > > > > > forbid it :/ > > > > > > > > > > > > > > > > > > > > > > > > > > Wouldn't the driver do the same EDID check before choosing whether it > > > > > > > > > > > > > uses RGB or YCbCr signalling? > > > > > > > > > > > > > > > > > > > > > > > > I suppose it could. The modeset would then fail, which is perhaps > > > > > > > > > > > > > > > > > > > > > > Could? What are they missing? > > > > > > > > > > > > > > > > > > > > The fact that the new property that also affects the rgb->ycbcr matrix > > > > > > > > > > doesn't even exist? > > > > > > > > > > > > > > > > > > I think the question was about the current Colorspace property. > > > > > > > > > > > > > > Yes. > > > > > > > > > > > > > > We need to be able to set ColourPrimaries infoframe field for the sink. > > > > > > > Only userspace knows what ColourPrimaries it uses, and the driver has > > > > > > > no need to care at all, other than tell the sink what we have. > > > > > > > > > > > > > > When a driver chooses to use YCbCr, it needs to use the > > > > > > > MatrixCoefficients the sink expects. > > > > > > > > > > > > > > If we send the infoframe to the sink telling the signal uses BT.2020 > > > > > > > ColourPrimaries, does that same bit pattern also tell the sink we are > > > > > > > using the BT.2020 NCL MatrixCoefficients if the driver chooses YCbCr? > > > > > > > > > > > > > > Do drivers actually use BT.2020 NCL MatrixCoefficients in that case? > > > > > > > > > > > > No. I think I've repeated this same line a thousand times already: > > > > > > The current colorspace property *only* affects the infoframe/msa/sdp, > > > > > > nothing else. > > > > > > > > > > That's the problem. I don't know what that means. > > > > > > > > > > Does it mean that the sink expects BT.2020 NCL MatrixCoefficients to > > > > > have been used? > > > > > > > > Yes, assuming that is the colorspace property value you picked. > > > > > > > > > > > > > > And the driver will never use BT.2020 NCL MatrixCoefficients in any > > > > > circumstances? > > > > > > > > Correct. > > > > > > > > > > > > > > See the conflict? The sink will be decoding the signal incorrectly, > > > > > because we are encoding it with the wrong MatrixCoefficients if the > > > > > driver happens to silently choose YCbCr and userspace wants to send > > > > > BT2020 ColourPrimaries indicated in the infoframe. > > > > > > > > Yes. And hence I thought pretty much everyone already > > > > agreed that a new property is needed. > > > > > > I think I was confused as well with the re-posting of this series, > > > thinking it could be salvageable somehow and tried to understand how. > > > Up to Harry, I think I've left enough annoying questions by now. :-) > > > > > > > To make sure we actually understand what we're implementing > > > > I think it should start out very minimal. Eg just three values: > > > > - unspecified RGB + BT.601 YCbCr > > > > - unspecified RGB + BT.709 YCbCr > > > > - BT.2020 RGB + BT.2020 YCbCr NCL > > It would be best to describe for every case both what the display and > what the driver expects as input. I don't want the uapi to make any claims about the display. Half the real world displays are going to interpret it some other way anyway. So all I think we can promise is: - exactly what colorimetry we will indicate to the display in the metadata - exactly what MatrixCoefficients we will use for RGB->YCbCr conversion After that it's between you and your god^W display vendor what happens. > > > > > > > ColourPrimaries + MatrixCoefficients, respectively. Sounds fine. > > > > > > I recall hearing that DP spec actually has something like "unspecified" > > > while HDMI has only "default colorimetry" which is specified, but I'm > > > guessing that many monitors and TVs just don't implement it like they > > > should, so it's effectively unspecified. > > > > DP in theory might have default RGB (whatever that might mean) vs. > > sRGB, although at some point I think it was just vague RGB vs. CEA RGB, > > which I think in i915 we might be using to indicate limited vs. full > > quantization range instead. I think that somehow fixed some monitors > > (while many others still get the quantization range horrible wrong of > > course). > > > > HDMI/CTA-861-? IIRC didn't have anything but just "RGB", and in some > > footnote CTA-861-? then goes on to talk about the sRGB bit in the EDID. > > In the end it didn't seem to say anything definitive what the RGB > > colorimetry really means. > > DP has "RGB unspecified color space (Legacy RGB mode)" without more explanation. > > CTA-861 has, as I said in a previous mail on this series: > > "If bits C0 and C1 are zero, the colorimetry shall correspond to the > default colorimetry defined in Section 5.1" > > and in Section 5.1 > > "In all cases described above, the RGB color space used should be the > RGB color space the Sink declares in the Basic Display Parameters and > Feature Block of its EDID." > > > > > > > "unspecified" in UAPI is ok as long as there will be another distinct > > > value for "HDMI default colorimetry" or such. > > > > > > I'm not sure why anyone would want to use "unspecified" but I guess > > > it's necessary for UAPI backward compatibility. > > > > Just because the specs don't really seem to specify anything > > sensible. We could just call it "RGB" and leave it at that of > > course. > > I think unspecified and default RGB are both good enough. The spec > doesn't give us much better guarantees anyway. Unspecified might even > be better because we could then add a default RGB case if we ever get > a mode which guarantees us that the colorimetry of the EDID is in > effect. > > > > > > > > > > > > And that would control: > > > > - basic colorimetry metadata transmitted to the sink > > > > - MatrixCoefficients used for the potential RGB->YCbCr conversion > > > > > > > > Transfer funcs, primaries, etc. would be left out (apart from > > > > the potential metadata aspect). > > > > > > Primaries left out? What are your "unspecified RGB" and "BT.2020 RGB" > > > above then? > > > > It all seems too open to interpretation to make it anything > > but "undefined". > > > > > > > > Asking from another angle, using infoframes, is it possible to tell the > > > sink to use BT.2020 YCbCr NCL without *also* implying BT.2020 > > > ColourPrimaries? Joshua seemed to be saying "no". > > > > I don't think so. The BT.2020 cases seems to be more strictrly > > defined. > > The Colorimetry gives us the primaries, white point, transfer > characteristics and conversion matrix if it is for YCC. The HDR > metadata can override the transfer characteristics. > > Anyways, CTA-861 is still confusing me a lot. > > It has "No Data" Colorimetry but is that the same as not sending the > InfoFrame at all? Either way, the colorimetry should be the one from > the EDID. > > But the transfer characteristics change with the selected Colorimetry. > In the table is "RGB" the same as "No Data" and the same as sending no > InfoFrame? But then when is the transfer characteristics of the EDID > in effect and when bt.709 from the table? > > There doesn't appear to be a default colorimetry for YCC. So how would > you even automatically fall back from RGB to YCC with the same > colorimetry? > > I only see the colorimetry BT.709 and not BT.601. Some other > colorimetry uses the BT.601 conversion matrix so how would > "unspecified RGB + BT.709 YCbCr" even work? It just means: - if we output RGB we the colorimetry signalled will be "no data" value (or whatever the "i don't know what anything means" value) - if we output YCbCr the colorimetry signalled will be the BT.709 value, and the YCbCr data will be produced using the BT.709 MatrixCoefficients Beyond that absolutely no promises about anything. -- Ville Syrjälä Intel
