[PATCH v2 12/26] drm/exynos: Split manager/display/subdrv

[Tomasz Figa]

Hi,

On Wednesday 23 of October 2013 12:09:06 Sean Paul wrote:
> On Wed, Oct 23, 2013 at 11:53 AM, Dave Airlie <airlied at gmail.com> wrote:
> >>>>> I think we need to start considering a framework where subdrivers
> >>>>> just
> >>>>> add drm objects themselves, then the toplevel node is responsible
> >>>>> for
> >>>>> knowing that everything for the current configuration is loaded.
> >>>> 
> >>>> It would be nice to specify the various pieces in dt, then have
> >>>> some
> >>>> type of drm notifier to the toplevel node when everything has been
> >>>> probed. Doing it in the dt would allow standalone
> >>>> drm_bridge/drm_panel
> >>>> drivers to be transparent as far as the device's drm driver is
> >>>> concerned.
> >>>> 
> >>>> Sean
> >>>> 
> >>>>> I realise we may need to make changes to the core drm to allow
> >>>>> this
> >>>>> but we should probably start to create a strategy for fixing the
> >>>>> API
> >>>>> issues that this throws up.
> >>>>> 
> >>>>> Note I'm not yet advocating for dynamic addition of nodes once the
> >>>>> device is in use, or removing them.
> >>> 
> >>> I do wonder if we had some sort of tag in the device tree for any
> >>> nodes
> >>> involved in the display, and the core drm layer would read that
> >>> list,
> >>> and when every driver registers tick things off, and when the last
> >>> one
> >>> joins we get a callback and init the drm layer, we'd of course have
> >>> the
> >>> basic drm layer setup prior to that so we can add the objects as the
> >>> drivers load. It might make development a bit trickier as you'd need
> >>> to make sure someone claimed ownership of all the bits for init to
> >>> proceed.>> 
> >> Yeah, that's basically what the strawman looked like in my head.
> >> 
> >> Instead of a property in each node, I was thinking of having a
> >> separate gfx pipe nodes that would have dt pointers to the various
> >> pieces involved in that pipe. This would allow us to associate
> >> standalone entities like bridges and panels with encoders in dt w/o
> >> doing it in the drm code. I *think* this should be Ok with the dt
> >> guys
> >> since it is still describing the hardware, but I think we'd have to
> >> make sure it wasn't drm-specific.
> > 
> > I suppose the question is how much dynamic pipeline construction there
> > is,
> > 
> > even on things like radeon and i915 we have dynamic clock generator to
> > crtc to encoder setups, so I worry about static lists per-pipe, so I
> > still think just stating all these devices are needed for display and
> > a list of valid interconnections between them, then we can have the
> > generic code model drm crtc/encoders/connectors on that list, and
> > construct the possible_crtcs /possible_clones etc at that stage.
> 
> I'm, without excuse, hopeless at devicetree, so there are probably
> some violations, but something like:
> 
> display-pipelines {
>   required-elements = <&bridge-a &panel-a &encoder-x &encoder-y
> &crtc-x &crtc-y>;
>   pipe1 {
>     bridge = <&bridge-a>;
>     encoder = <&encoder-x>;
>     crtc = <&crtc-y>;
>   };
>   pipe2 {
>     encoder = <&encoder-x>;
>     crtc = <&crtc-x>;
>   };
>   pipe3 {
>     panel = <&panel-a>;
>     encoder = <&encoder-y>;
>     crtc = <&crtc-y>;
>   };
> };
> 
> I'm tempted to add connector to the pipe nodes as well, so it's
> obvious which connector should be used in cases where multiple
> entities in the pipe implement drm_connector. However, I'm not sure if
> that would be NACKed by dt people.
> 
> I'm also not sure if there are too many combinations for i915 and
> radeon to make this unreasonable. I suppose those devices could just
> use required-elements and leave the pipe nodes out.

Just to put my two cents in, as one of the people involved into "the 
device tree movement", I'd say that instead of creating artifical 
entities, such as display-pipelines and all of the pipeX'es, device tree 
should represent relations between nodes.

According to the generic DT bindings we already have for video-interfaces 
[1] your example connection layout would look as follows:

panel-a {
	/* Single input port */
	port {
		panel_a: endpoint at 0 {
			remote-endpoint = <&encoder_y_out>;
		};
	};
};

bridge-a {
	ports {
		/* Input port */
		port at 0 {
			bridge_a_in: endpoint at 0 {
				remote-endpoint = <&encoder_x_out>;
			};
		};

		/*
		 * Since it is a bridge, port at 1 should be probably
		 * present here as well...
		 */
	};
};

encoder-x {
	ports {
		/* Input port */
		port at 0 {
			encoder_x_in0: endpoint at 0 {
				remote-endpoint = <&crtc_x>;
			};

			encoder_x_in1: endpoint at 1 {
				remote-endpoint = <&crtc_y_out0>;
			};
		};

		/* Output port */
		port at 1 {
			encoder_x_out: endpoint at 0 {
				remote-endpoint = <&bridge_a_in>;
			};
		};
	};
};

encoder-y {
	ports {
		/* Input port */
		port at 0 {
			encoder_y_in: endpoint at 0 {
				remote-endpoint = <&encoder_y_in>;
			};
		};

		/* Output port */
		port at 1 {
			encoder_y_out: endpoint at 0 {
				remote-endpoint = <&panel_a>;
			};
		};
	};
};

crtc-x {
	/* Single output port */
	port {
		crtc_x: endpoint at 0 {
			remote-endpoint = <&encoder_x_in0>;
		};
	};
};

crtc-y {
	/* Single output port */
	port {
		crtc_y_out0: endpoint at 0 {
			remote-endpoint = <&encoder_x_in1>;
		};

		crtc_y_out1: endpoint at 1 {
			remote-endpoint = <&encoder_y_in>;
		};
	};
};

If I didn't make any typos, then the nodes above should not only represent 
fully the layout of your sample video pipelines, but also map connections 
between video entities with their physical endpoints, allowing respective 
drivers to properly configure any muxes based purely on DT data. Of course 
this also includes dependencies between all display entities.

[1] Documentation/devicetree/bindings/media/video-interfaces.txt

Best regards,
Tomasz