On Fri, Feb 09, 2024 at 09:34:35PM +0100, Sebastian Wick wrote: > On Mon, Feb 05, 2024 at 10:39:38AM +0100, Maxime Ripard wrote: > > On Fri, Feb 02, 2024 at 06:37:52PM +0200, Ville Syrjälä wrote: > > > On Fri, Feb 02, 2024 at 04:59:30PM +0100, Maxime Ripard wrote: > > > > On Fri, Feb 02, 2024 at 05:40:47PM +0200, Ville Syrjälä wrote: > > > > > On Fri, Feb 02, 2024 at 02:01:39PM +0100, Maxime Ripard wrote: > > > > > > Hi, > > > > > > > > > > > > On Mon, Jan 15, 2024 at 03:37:20PM +0100, Sebastian Wick wrote: > > > > > > > > > /** > > > > > > > > > * DOC: HDMI connector properties > > > > > > > > > * > > > > > > > > > + * Broadcast RGB > > > > > > > > > + * Indicates the RGB Quantization Range (Full vs Limited) used. > > > > > > > > > + * Infoframes will be generated according to that value. > > > > > > > > > + * > > > > > > > > > + * The value of this property can be one of the following: > > > > > > > > > + * > > > > > > > > > + * Automatic: > > > > > > > > > + * RGB Range is selected automatically based on the mode > > > > > > > > > + * according to the HDMI specifications. > > > > > > > > > + * > > > > > > > > > + * Full: > > > > > > > > > + * Full RGB Range is forced. > > > > > > > > > + * > > > > > > > > > + * Limited 16:235: > > > > > > > > > + * Limited RGB Range is forced. Unlike the name suggests, > > > > > > > > > + * this works for any number of bits-per-component. > > > > > > > > > + * > > > > > > > > > + * Drivers can set up this property by calling > > > > > > > > > + * drm_connector_attach_broadcast_rgb_property(). > > > > > > > > > + * > > > > > > > > > > > > > > > > This is a good time to document this in more detail. There might be two > > > > > > > > different things being affected: > > > > > > > > > > > > > > > > 1. The signalling (InfoFrame/SDP/...) > > > > > > > > 2. The color pipeline processing > > > > > > > > > > > > > > > > All values of Broadcast RGB always affect the color pipeline processing > > > > > > > > such that a full-range input to the CRTC is converted to either full- or > > > > > > > > limited-range, depending on what the monitor is supposed to accept. > > > > > > > > > > > > > > > > When automatic is selected, does that mean that there is no signalling, > > > > > > > > or that the signalling matches what the monitor is supposed to accept > > > > > > > > according to the spec? Also, is this really HDMI specific? > > > > > > > > > > > > > > > > When full or limited is selected and the monitor doesn't support the > > > > > > > > signalling, what happens? > > > > > > > > > > > > > > Forgot to mention: user-space still has no control over RGB vs YCbCr on > > > > > > > the cable, so is this only affecting RGB? If not, how does it affect > > > > > > > YCbCr? > > > > > > > > > > > > So I dug a bit into both the i915 and vc4 drivers, and it looks like if > > > > > > we're using a YCbCr format, i915 will always use a limited range while > > > > > > vc4 will follow the value of the property. > > > > > > > > > > The property is literally called "Broadcast *RGB*". > > > > > That should explain why it's only affecting RGB. > > > > > > > > Right. And the limited range option is called "Limited 16:235" despite > > > > being usable on bpc > 8 bits. Naming errors occurs, and history happens > > > > to make names inconsistent too, that's fine and not an argument in > > > > itself. > > > > > > > > > Full range YCbCr is a much rarer beast so we've never bothered > > > > > to enable it. > > > > > > > > vc4 supports it. > > > > > > Someone implemented it incorrectly then. > > > > Incorrectly according to what documentation / specification? I'm sorry, > > but I find it super ironic that i915 gets to do its own thing, not > > document any of it, and when people try to clean things up they get told > > that we got it all wrong. > > FWIW, this was an i915 property and if another driver uses the same > property name it must have the same behavior. Yes, it isn't standardized > and yes, it's not documented (hence this effort here) but it's still on > vc4 to make the property compatible. How is it not compatible? It's a superset of what i915 provides, but it's strictly compatible with it. I would argue that i915 is the broken one since userspace could force a full range output, but since the driver takes the YUV vs RGB decision itself and only supports limited range for YUV, the driver would effectively ignore that user-space property, without the user-space being able to tell it was ignored in the first place. > Trying to make the property handle YCbCr is very much in the "let's try > to fix the property" territory that I want to avoid, so I'm in favor of > adjusting vc4. Breaking the ABI in the process. For something that is explicitly supported by the spec, the driver, and the hardware. On a property that never said it wasn't meant to be used that way, and with semantics based on a driver that never provided a way to check those restrictions in the first place. And it's not like i915 is going to use that code anyway. Maxime
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