On Thu, Feb 22, 2024 at 02:58:45PM +0200, Ville Syrjälä wrote: > On Thu, Feb 22, 2024 at 11:54:04AM +0100, Maxime Ripard wrote: > > On Mon, Feb 19, 2024 at 03:01:44PM +0100, Sebastian Wick wrote: > > > On Thu, Feb 15, 2024 at 12:00:01PM +0100, Maxime Ripard wrote: > > > > On Mon, Feb 12, 2024 at 06:06:18PM +0100, Sebastian Wick wrote: > > > > > On Mon, Feb 12, 2024 at 05:53:48PM +0100, Maxime Ripard wrote: > > > > > > On Mon, Feb 12, 2024 at 05:49:33PM +0200, Ville Syrjälä wrote: > > > > > > > On Mon, Feb 12, 2024 at 11:01:07AM +0100, Maxime Ripard wrote: > > > > > > > > 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. > > > > > > > > > > > > > > No it is not. > > > > > > > > > > > > The property is compatible with i915 interpretation of it, whether you > > > > > > like it or not. And that's what Sebastian was referring to. > > > > > > > > > > > > > Eg. what happens if you set the thing to full range for RGB (which you > > > > > > > must on many broken monitors), and then the kernel automagically > > > > > > > switches to YCbCr (for whatever reason) but the monitor doesn't > > > > > > > support full range YCbCr? Answer: you get crap output. > > > > > > > > > > > > And that part is just moving goalposts. > > > > > > > > > > But it's really not. > > > > > > > > It really is. This whole discussion started by "well it would be nice if > > > > we made that property handled by the core", and we're now at the "we > > > > need to deal with broken YCbCr displays and i915 opinion about them" > > > > stage. After creating documentation, unit tests, etc. It's the textbook > > > > definition of moving goalposts. And while i915 won't be affected by all > > > > that work. > > > > > > Sorry, but what you're saying is just not true. > > > > > > The Broadcast RGB property is an Intel specific property. > > > > No, it's not. vc4 has been using it for a year now. > > > > > It lacked documentation but the user space contract exists and it > > > based on how i915 implemented it. By changing the semantics you're > > > breaking user space. The documentation has to document the current > > > contract between i915 and user space, not whatever you want the > > > property to be like. > > > > > > I get that you're frustrated that you have to do work while i915 doesn't > > > but none of that is relevant for what the property is and how user space > > > expects it to work. > > > > That's not it, really. I don't mind doing the work. I do mind losing > > functionalities on something that was working fine. And getting the > > blame for something that is, at best, just as much of an documentation > > issue on i915 devs. > > We've had a couple of these cases recently where people have taken > some old property implemented by i915 and implemented it differently > in some other driver. Dunno if the reason was that people didn't try > to understand what i915 is doing and why, or they misundestood it, > or they understood it but decided to ignore it anyway. > > Unfortunately having undocumented corners in the uapi is simply > a fact of life when dealing with a >15 year old legacy codebase. > Also there were basically no rules regarding properties in the > past, so everyone just added random properties whenever they > felt like it. > > I think going forward we should probably lay down some extra > ground rules; if an old undocumented uapi is being extended > to cover more than one driver we must first figure out what > the de facto semantics are, and document things properly > before anything else gets done. That would be great. The documentation already has requirements for new properties. Adding the requirement for extending driver-specific properties to more drivers there would be great and make it "official". > > -- > Ville Syrjälä > Intel >
