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. > > > Eg. with DP it only became possible with the introduction of the VSC > > SDP (and I don't recall if there's additional capability checks that > > are also required). With DP MSA signalling full range YCbCr is not > > possible at all. > > This is for HDMI only. > > > I don't recall right now what the HDMI requirements are. > > HDMI has supported it for a while, and it's defined (for example) in the > HDMI 1.4 spec in Section 6.6 - Video Quantization Ranges. It supports > limited and full range on both RGB and YCbCr, as long as the EDIDs state > so and the Infoframes signal it. I think a good reason for not using a simple boolean like this YCbCr is that it doesn't cover the color encoding part at all, which is probably more important than the quantization range. So we need a new property anyway. -- Ville Syrjälä Intel
