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X-CSE-ConnectionGUID: YTksuC+4TcGyyuCOjVECzA== X-CSE-MsgGUID: cWzchwrIQQCQh7s605LmYw== X-IronPort-AV: E=McAfee;i="6800,10657,11744"; a="75684694" X-IronPort-AV: E=Sophos;i="6.23,151,1770624000"; d="scan'208";a="75684694" Received: from orviesa009.jf.intel.com ([10.64.159.149]) by orvoesa112.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 31 Mar 2026 04:44:55 -0700 X-CSE-ConnectionGUID: 6h6u+1WGThKi+KKqZ0aLgw== X-CSE-MsgGUID: LxtBhquxT9ukvY131dMHYQ== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="6.23,151,1770624000"; d="scan'208";a="226222302" Received: from rvuia-mobl.ger.corp.intel.com (HELO localhost) ([10.245.244.24]) by orviesa009-auth.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 31 Mar 2026 04:44:43 -0700 Date: Tue, 31 Mar 2026 14:44:29 +0300 From: Ville =?iso-8859-1?Q?Syrj=E4l=E4?= To: Nicolas Frattaroli Cc: Maxime Ripard , Harry Wentland , Leo Li , Rodrigo Siqueira , Alex Deucher , Christian =?iso-8859-1?Q?K=F6nig?= , David Airlie , Simona Vetter , Maarten Lankhorst , Thomas Zimmermann , Andrzej Hajda , Neil Armstrong , Robert Foss , Laurent Pinchart , Jonas Karlman , Jernej Skrabec , Sandy Huang , Heiko =?iso-8859-1?Q?St=FCbner?= , Andy Yan , Jani Nikula , Rodrigo Vivi , Joonas Lahtinen , Tvrtko Ursulin , Dmitry Baryshkov , Sascha Hauer , Rob Herring , Jonathan Corbet , Shuah Khan , kernel@collabora.com, amd-gfx@lists.freedesktop.org, dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-rockchip@lists.infradead.org, intel-gfx@lists.freedesktop.org, intel-xe@lists.freedesktop.org, linux-doc@vger.kernel.org, Werner Sembach , Andri Yngvason , Marius Vlad , Pekka Paalanen , Simon Ser , Sebastian Wick , Jonas =?iso-8859-1?Q?=C5dahl?= , Xaver Hugl Subject: Re: [PATCH v11 03/22] drm: Add new general DRM property "color format" Message-ID: References: <20260324-color-format-v11-0-605559af4fb4@collabora.com> <5583906.GXAFRqVoOG@workhorse> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <5583906.GXAFRqVoOG@workhorse> X-Patchwork-Hint: comment Organization: Intel Finland Oy - BIC 0357606-4 - c/o Alberga Business Park, 6 krs Bertel Jungin Aukio 5, 02600 Espoo, Finland On Tue, Mar 31, 2026 at 12:33:00PM +0200, Nicolas Frattaroli wrote: > On Tuesday, 31 March 2026 01:56:16 Central European Summer Time Ville Syrjälä wrote: > > On Sat, Mar 28, 2026 at 02:49:04AM +0200, Ville Syrjälä wrote: > > > On Fri, Mar 27, 2026 at 01:56:06PM +0100, Nicolas Frattaroli wrote: > > > > On Thursday, 26 March 2026 18:58:25 Central European Standard Time Ville Syrjälä wrote: > > > > > On Thu, Mar 26, 2026 at 06:02:47PM +0100, Maxime Ripard wrote: > > > > > > On Wed, Mar 25, 2026 at 08:43:15PM +0200, Ville Syrjälä wrote: > > > > > > > On Wed, Mar 25, 2026 at 03:56:58PM +0100, Maxime Ripard wrote: > > > > > > > > On Wed, Mar 25, 2026 at 01:03:07PM +0200, Ville Syrjälä wrote: > > > > > > > > > On Wed, Mar 25, 2026 at 09:24:27AM +0100, Maxime Ripard wrote: > > > > > > > > > > On Tue, Mar 24, 2026 at 09:53:35PM +0200, Ville Syrjälä wrote: > > > > > > > > > > > On Tue, Mar 24, 2026 at 08:10:11PM +0100, Nicolas Frattaroli wrote: > > > > > > > > > > > > On Tuesday, 24 March 2026 18:00:45 Central European Standard Time Ville Syrjälä wrote: > > > > > > > > > > > > > On Tue, Mar 24, 2026 at 05:01:07PM +0100, Nicolas Frattaroli wrote: > > > > > > > > > > > > > > +enum drm_connector_color_format { > > > > > > > > > > > > > > + /** > > > > > > > > > > > > > > + * @DRM_CONNECTOR_COLOR_FORMAT_AUTO: The driver or display protocol > > > > > > > > > > > > > > + * helpers should pick a suitable color format. All implementations of a > > > > > > > > > > > > > > + * specific display protocol must behave the same way with "AUTO", but > > > > > > > > > > > > > > + * different display protocols do not necessarily have the same "AUTO" > > > > > > > > > > > > > > + * semantics. > > > > > > > > > > > > > > + * > > > > > > > > > > > > > > + * For HDMI, "AUTO" picks RGB, but falls back to YCbCr 4:2:0 if the > > > > > > > > > > > > > > + * bandwidth required for full-scale RGB is not available, or the mode > > > > > > > > > > > > > > + * is YCbCr 4:2:0-only, as long as the mode and output both support > > > > > > > > > > > > > > + * YCbCr 4:2:0. > > > > > > > > > > > > > > + * > > > > > > > > > > > > > > + * For display protocols other than HDMI, the recursive bridge chain > > > > > > > > > > > > > > + * format selection picks the first chain of bridge formats that works, > > > > > > > > > > > > > > + * as has already been the case before the introduction of the "color > > > > > > > > > > > > > > + * format" property. Non-HDMI bridges should therefore either sort their > > > > > > > > > > > > > > + * bus output formats by preference, or agree on a unified auto format > > > > > > > > > > > > > > + * selection logic that's implemented in a common state helper (like > > > > > > > > > > > > > > + * how HDMI does it). > > > > > > > > > > > > > > + */ > > > > > > > > > > > > > > + DRM_CONNECTOR_COLOR_FORMAT_AUTO = 0, > > > > > > > > > > > > > > + > > > > > > > > > > > > > > + /** > > > > > > > > > > > > > > + * @DRM_CONNECTOR_COLOR_FORMAT_RGB444: RGB output format > > > > > > > > > > > > > > + */ > > > > > > > > > > > > > > + DRM_CONNECTOR_COLOR_FORMAT_RGB444, > > > > > > > > > > > > > > + > > > > > > > > > > > > > > + /** > > > > > > > > > > > > > > + * @DRM_CONNECTOR_COLOR_FORMAT_YCBCR444: YCbCr 4:4:4 output format (ie. > > > > > > > > > > > > > > + * not subsampled) > > > > > > > > > > > > > > + */ > > > > > > > > > > > > > > + DRM_CONNECTOR_COLOR_FORMAT_YCBCR444, > > > > > > > > > > > > > > + > > > > > > > > > > > > > > + /** > > > > > > > > > > > > > > + * @DRM_CONNECTOR_COLOR_FORMAT_YCBCR422: YCbCr 4:2:2 output format (ie. > > > > > > > > > > > > > > + * with horizontal subsampling) > > > > > > > > > > > > > > + */ > > > > > > > > > > > > > > + DRM_CONNECTOR_COLOR_FORMAT_YCBCR422, > > > > > > > > > > > > > > + > > > > > > > > > > > > > > + /** > > > > > > > > > > > > > > + * @DRM_CONNECTOR_COLOR_FORMAT_YCBCR420: YCbCr 4:2:0 output format (ie. > > > > > > > > > > > > > > + * with horizontal and vertical subsampling) > > > > > > > > > > > > > > + */ > > > > > > > > > > > > > > + DRM_CONNECTOR_COLOR_FORMAT_YCBCR420, > > > > > > > > > > > > > > > > > > > > > > > > > > Seems like this should document what the quantization range > > > > > > > > > > > > > should be for each format. > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > I don't think so? If you want per-component bit depth values, > > > > > > > > > > > > DRM_FORMAT_* defines would be the appropriate values to use. This > > > > > > > > > > > > enum is more abstract than that, and is there to communicate > > > > > > > > > > > > YUV vs. RGB and chroma subsampling, with bit depth being handled > > > > > > > > > > > > by other properties. > > > > > > > > > > > > > > > > > > > > > > > > If you mean the factor used for subsampling, then that'd only be > > > > > > > > > > > > relevant if YCBCR410 was supported where one chroma plane isn't > > > > > > > > > > > > halved but quartered in resolution. I suspect 4:1:0 will never > > > > > > > > > > > > be added; no digital display protocol standard supports it to my > > > > > > > > > > > > knowledge, and hopefully none ever will. > > > > > > > > > > > > > > > > > > > > > > No, I mean the quantization range (16-235 vs. 0-255 etc). > > > > > > > > > > > > > > > > > > > > > > The i915 behaviour is that YCbCr is always limited range, > > > > > > > > > > > RGB can either be full or limited range depending on the > > > > > > > > > > > "Broadcast RGB" property and other related factors. > > > > > > > > > > > > > > > > > > > > So far the HDMI state has both the format and quantization range as > > > > > > > > > > different fields. I'm not sure we need to document the range in the > > > > > > > > > > format field, maybe only mention it's not part of the format but has a > > > > > > > > > > field of its own? > > > > > > > > > > > > > > > > > > I think we only have it for RGB (on some drivers only?). For YCbCr > > > > > > > > > I think the assumption is limited range everywhere. > > > > > > > > > > > > > > > > > > But I'm not really concerned about documenting struct members. > > > > > > > > > What I'm talking about is the *uapi* docs. Surely userspace > > > > > > > > > will want to know what the new property actually does so the > > > > > > > > > uapi needs to be documented properly. And down the line some > > > > > > > > > new driver might also implement the wrong behaviour if there > > > > > > > > > is no clear specification. > > > > > > > > > > > > > > > > Ack > > > > > > > > > > > > > > > > > So I'm thinking (or perhaps hoping) the rule might be something like: > > > > > > > > > - YCbCr limited range > > > > > > > > > - RGB full range if "Broadcast RGB" property is not present > > > > > > > > > > > > > > > > Isn't it much more complicated than that for HDMI though? My > > > > > > > > recollection was that any VIC but VIC1 would be limited range, and > > > > > > > > anything else full range? > > > > > > > > > > > > > > Do we have some driver that implements the CTA-861 CE vs. IT mode > > > > > > > logic but doesn't expose the "Broadcast RGB" property? I was hoping > > > > > > > those would always go hand in hand now. > > > > > > > > > > > > I'm not sure. i915 and the HDMI state helpers handle it properly (I > > > > > > think?) but it looks like only vc4 registers the Broadcast RGB property > > > > > > and uses the HDMI state helpers. > > > > > > > > > > > > And it looks like amdgpu registers Broadcast RGB but doesn't use > > > > > > drm_default_rgb_quant_range() which seems suspicious? > > > > > > > > > > If they want just manual full vs. limited then they should > > > > > limit the property to not expose the "auto" option at all. > > > > > > > > > > amdgpu also ties this in with the "colorspace" property, which > > > > > originally in i915 only controlled the infoframes/etc. But on > > > > > amdgpu it now controls various aspects of output color > > > > > transformation. The end result is that the property is a complete > > > > > mess with most of the values making no sense. And for whatever > > > > > reason everyone involved refused to remove/deprecate the > > > > > nonsensical values :/ > > > > > > > > > > Looks like this series should make sure the documentation for > > > > > the "colorspace" property is in sync with the new property > > > > > as well. Currently now it's giving conflicting information. > > > > > > > > > > > > > I take it the problematic information is in > > > > > > > > * DOC: standard connector properties > > > > * > > > > * Colorspace: > > > > > > > > and probably specifically BT2020_YCC's (and BT2020_RGB's?) insistence > > > > that they "produce RGB content". > > > > > > > > I think we probably just have to change the statement "The variants > > > > BT2020_RGB and BT2020_YCC are equivalent and the driver chooses between > > > > RGB and YCbCr on its own." > > > > > > > > The "on its own" here would get turned into "based on the color format > > > > property". > > > > > > > > Speaking of i915, that patch is one of the very few (5) patches in > > > > this series still lacking a review (hint hint nudge nudge). I'd like > > > > to get some more feedback on the remaining patches before I send out > > > > another revision, so that it's hopefully not just docs changes (I > > > > know better than to think those patches must be perfect and won't > > > > need revision.) > > > > > > The i915 code around this is already a big mess, and I don't really > > > adding to that mess. So I think we'll need to do some refactoring before > > > we add anything there. I already started typing something and so far > > > it looks fairly straightforward, so I should have something soon. > > > > OK, posted something > > https://lore.kernel.org/intel-gfx/20260330235339.29479-1-ville.syrjala@linux.intel.com/T/#m7c349478ca6c856fbc68d5e2178f1aa31678a05f > > Thanks! I'll take a look at this today to get a more solid idea of > where the pain points you highlighted are. > > I'll also rebase/reimplement my i915 color format implementation > (sans the DP-MST part, as discussed) on top of this on the next > revision. I was never fully happy with the current one due to the > logic being shoehorned into the already existing i915 fallback > format logic, so I'm quite happy to have another opportunity to > implement it with less historic baggage. > > > Are the wayland/compositor/color management folks on board with > > these new properties? I don't think I see the usual suspects on > > the cc list. > > I don't know which precise group of people you refer to, Off the top of my head, Pekka,Simon,Sebastian,Jonas,Xaver might be relevant here. Added to Cc... > but at > least from the Collabora side of things, the userspace Wayland > people are on board with these new properties. In Weston, we use > it to implement the Weston frontend's "color-format" option in a > WIP branch at > > https://gitlab.freedesktop.org/wayland/weston/-/merge_requests/1859 > > I've also been made aware that LibreELEC is aware, and will look > into making use of it rather than their own kernel patches. > > Kind regards, > Nicolas Frattaroli > > > > > > > While doing that several questions came to my mind though: > > > > > > * More interactions with the colorspace property, but I sent > > > a separate mail already about that > > > > > > * Which conversion matrix to use, and the answer I suspect > > > should be "ask the colorspace property", as mentioned in the > > > other mail > > > > > > * Should we flat out reject color formats (and I suppose also > > > colorspace prop values) the sink doesn't claim to support? > > > > > > If yes, then I think we'll have to forget about adding anything > > > to i915 MST code. The way the MST stuff works is that if one > > > stream needs a modeset then all the related streams get modeset > > > as well. Thus if the user replaces a monitor getting fed with a > > > YCbCr stream just as another stream is being modeset, then the > > > entire atomic commit could fail due to the YCbCr stream getting > > > rejected. > > > > > > I think eventually we might have to invent some mechanism where > > > all the input into the modeset computation is cached somehow, > > > and said cache updated only on explicit userspace modesets. > > > Either that or we have to come up with a way to skip some of > > > the calculations that depend on external factors. Either way > > > it's going to be a pain. > > > > > > OTOH if we don't mind feeding the sink with stuff it can't > > > understand, then I suppose we might add YCbCr 4:4:4 support > > > for MST. It shouldn't be any different from RGB apart from > > > the RGB->YCbCr conversion, which is handled elsewhere. But > > > YCbCr 4:2:0 is definitely out either way, the MST code has > > > no support for that currently. > > > > > > > > > > -- Ville Syrjälä Intel