Re: [PATCH 06/15] drm/sun4i: tcon: Add support for tcon-top

From: Maxime Ripard
Date: Mon Jun 04 2018 - 12:24:06 EST

On Mon, Jun 04, 2018 at 05:09:56PM +0200, Jernej Åkrabec wrote:
> Dne ponedeljek, 04. junij 2018 ob 13:50:34 CEST je Maxime Ripard napisal(a):
> > On Fri, Jun 01, 2018 at 09:19:43AM -0700, Chen-Yu Tsai wrote:
> > > On Fri, Jun 1, 2018 at 8:29 AM, Maxime Ripard <maxime.ripard@xxxxxxxxxxx>
> wrote:
> > > > On Thu, May 31, 2018 at 07:54:08PM +0200, Jernej Åkrabec wrote:
> > > >> Dne Äetrtek, 31. maj 2018 ob 11:21:33 CEST je Maxime Ripard napisal(a):
> > > >> > On Thu, May 24, 2018 at 03:01:09PM -0700, Chen-Yu Tsai wrote:
> > > >> > > >> > > + if (tcon->quirks->needs_tcon_top) {
> > > >> > > >> > > + struct device_node *np;
> > > >> > > >> > > +
> > > >> > > >> > > + np = of_parse_phandle(dev->of_node,
> > > >> > > >> > > "allwinner,tcon-top",
> > > >> > > >> > > 0);
> > > >> > > >> > > + if (np) {
> > > >> > > >> > > + struct platform_device *pdev;
> > > >> > > >> > > +
> > > >> > > >> > > + pdev = of_find_device_by_node(np);
> > > >> > > >> > > + if (pdev)
> > > >> > > >> > > + tcon->tcon_top =
> > > >> > > >> > > platform_get_drvdata(pdev);
> > > >> > > >> > > + of_node_put(np);
> > > >> > > >> > > +
> > > >> > > >> > > + if (!tcon->tcon_top)
> > > >> > > >> > > + return -EPROBE_DEFER;
> > > >> > > >> > > + }
> > > >> > > >> > > + }
> > > >> > > >> > > +
> > > >> > > >> >
> > > >> > > >> > I might have missed it, but I've not seen the bindings
> > > >> > > >> > additions for
> > > >> > > >> > that property. This shouldn't really be done that way anyway,
> > > >> > > >> > instead
> > > >> > > >> > of using a direct phandle, you should be using the of-graph,
> > > >> > > >> > with the
> > > >> > > >> > TCON-top sitting where it belongs in the flow of data.
> > > >> > > >>
> > > >> > > >> Just to answer to the first question, it did describe it in
> > > >> > > >> "[PATCH
> > > >> > > >> 07/15] dt- bindings: display: sun4i-drm: Add R40 HDMI pipeline".
> > > >> > > >>
> > > >> > > >> As why I designed it that way - HW representation could be
> > > >> > > >> described
> > > >> > > >> that way> >>
> > > >> > > >>
> > > >> > > >> (ASCII art makes sense when fixed width font is used to view
> it):
> > > >> > > >> / LCD0/LVDS0
> > > >> > > >>
> > > >> > > >> / TCON-LCD0
> > > >> > > >>
> > > >> > > >> | \ MIPI DSI
> > > >> > > >>
> > > >> > > >> mixer0 |
> > > >> > > >>
> > > >> > > >> \ / TCON-LCD1 - LCD1/LVDS1
> > > >> > > >>
> > > >> > > >> TCON-TOP
> > > >> > > >>
> > > >> > > >> / \ TCON-TV0 - TVE0/RGB
> > > >> > > >>
> > > >> > > >> mixer1 | \
> > > >> > > >>
> > > >> > > >> | TCON-TOP - HDMI
> > > >> > > >> |
> > > >> > > >> | /
> > > >> > > >>
> > > >> > > >> \ TCON-TV1 - TVE1/RGB
> > > >> > > >>
> > > >> > > >> This is a bit simplified, since there is also TVE-TOP, which is
> > > >> > > >> responsible
> > > >> > > >> for sharing 4 DACs between both TVE encoders. You can have two
> > > >> > > >> TV outs
> > > >> > > >> (PAL/ NTSC) or TVE0 as TV out and TVE1 as RGB or vice versa. It
> > > >> > > >> even
> > > >> > > >> seems that you can arbitrarly choose which DAC is responsible
> > > >> > > >> for
> > > >> > > >> which signal, so there is a ton of possible end combinations,
> > > >> > > >> but I'm
> > > >> > > >> not 100% sure.
> > > >> > > >>
> > > >> > > >> Even though I wrote TCON-TOP twice, this is same unit in HW. R40
> > > >> > > >> manual
> > > >> > > >> suggest more possibilities, although some of them seem wrong,
> > > >> > > >> like RGB
> > > >> > > >> feeding from LCD TCON. That is confirmed to be wrong when
> > > >> > > >> checking BSP
> > > >> > > >> code.
> > > >> > > >>
> > > >> > > >> Additionally, TCON-TOP comes in the middle of TVE0 and LCD0,
> > > >> > > >> TVE1 and
> > > >> > > >> LCD1 for pin muxing, although I'm not sure why is that needed at
> > > >> > > >> all,
> > > >> > > >> since according to R40 datasheet, TVE0 and TVE1 pins are
> > > >> > > >> dedicated and
> > > >> > > >> not on PORT D and PORT H, respectively, as TCON-TOP
> > > >> > > >> documentation
> > > >> > > >> suggest. However, HSYNC and PSYNC lines might be shared between
> > > >> > > >> TVE
> > > >> > > >> (when it works in RGB mode) and LCD. But that is just my guess
> > > >> > > >> since
> > > >> > > >> I'm not really familiar with RGB and LCD interfaces.
> > > >> > > >>
> > > >> > > >> I'm really not sure what would be the best representation in
> > > >> > > >> OF-graph.
> > > >> > > >> Can you suggest one?
> > > >> > > >
> > > >> > > > Rob might disagree on this one, but I don't see anything wrong
> > > >> > > > with
> > > >> > > > having loops in the graph. If the TCON-TOP can be both the input
> > > >> > > > and
> > > >> > > > output of the TCONs, then so be it, and have it described that
> > > >> > > > way in
> > > >> > > > the graph.
> > > >> > > >
> > > >> > > > The code is already able to filter out nodes that have already
> > > >> > > > been
> > > >> > > > added to the list of devices we need to wait for in the component
> > > >> > > > framework, so that should work as well.
> > > >> > > >
> > > >> > > > And we'd need to describe TVE-TOP as well, even though we don't
> > > >> > > > have a
> > > >> > > > driver for it yet. That will simplify the backward compatibility
> > > >> > > > later
> > > >> > > > on.
> > > >> > >
> > > >> > > I'm getting the feeling that TCON-TOP / TVE-TOP is the glue layer
> > > >> > > that
> > > >> > > binds everything together, and provides signal routing, kind of
> > > >> > > like
> > > >> > > DE-TOP on A64. So the signal mux controls that were originally
> > > >> > > found
> > > >> > > in TCON0 and TVE0 were moved out.
> > > >> > >
> > > >> > > The driver needs to know about that, but the graph about doesn't
> > > >> > > make
> > > >> > > much sense directly. Without looking at the manual, I understand it
> > > >> > > to
> > > >> > > likely be one mux between the mixers and TCONs, and one between the
> > > >> > > TCON-TVs and HDMI. Would it make more sense to just have the graph
> > > >> > > connections between the muxed components, and remove TCON-TOP from
> > > >> > > it, like we had in the past? A phandle could be used to reference
> > > >> > > the TCON-TOP for mux controls, in addition to the clocks and
> > > >> > > resets.
> > > >> > >
> > > >> > > For TVE, we would need something to represent each of the output
> > > >> > > pins,
> > > >> > > so the device tree can actually describe what kind of signal, be it
> > > >> > > each component of RGB/YUV or composite video, is wanted on each
> > > >> > > pin,
> > > >> > > if any. This is also needed on the A20 for the Cubietruck, so we
> > > >> > > can
> > > >> > > describe which pins are tied to the VGA connector, and which one
> > > >> > > does
> > > >> > > R, G, or B.
> > > >> >
> > > >> > I guess we'll see how the DT maintainers feel about this, but my
> > > >> > impression is that the OF graph should model the flow of data between
> > > >> > the devices. If there's a mux somewhere, then the data is definitely
> > > >> > going through it, and as such it should be part of the graph.
> > > >>
> > > >> I concur, but I spent few days thinking how to represent this sanely in
> > > >> graph, but I didn't find any good solution. I'll represent here my
> > > >> idea and please tell your opinion before I start implementing it.
> > > >>
> > > >> First, let me be clear that mixer0 and mixer1 don't have same
> > > >> capabilities
> > > >> (different number of planes, mixer0 supports writeback, mixer1 does
> > > >> not,
> > > >> etc.). Thus, it does matter which mixer is connected to which
> > > >> TCON/encoder.
> > > >> mixer0 is meant to be connected to main display and mixer1 to
> > > >> auxiliary. That obviously depends on end system.
> > > >>
> > > >> So, TCON TOP has 3 muxes, which have to be represented in graph. Two of
> > > >> them are for mixer/TCON relationship (each of them 1 input and 4
> > > >> possible outputs) and one for TV TCON/HDMI pair selection (2 possible
> > > >> inputs, 1 output).
> > > >>
> > > >> According to current practice in sun4i-drm driver, graph has to have
> > > >> port 0, representing input and port 1, representing output. This would
> > > >> mean that graph looks something like that:
> > > >>
> > > >> tcon_top: tcon-top@1c70000 {
> > > >>
> > > >> compatible = "allwinner,sun8i-r40-tcon-top";
> > > >> ...
> > > >> ports {
> > > >>
> > > >> #address-cells = <1>;
> > > >> #size-cells = <0>;
> > > >>
> > > >> tcon_top_in: port@0 {
> > > >>
> > > >> #address-cells = <1>;
> > > >> #size-cells = <0>;
> > > >> reg = <0>;
> > > >>
> > > >> tcon_top_in_mixer0: endpoint@0 {
> > > >>
> > > >> reg = <0>;
> > > >> remote-endpoint = <&mixer0_out_tcon_top>;
> > > >>
> > > >> };
> > > >>
> > > >> tcon_top_in_mixer1: endpoint@1 {
> > > >>
> > > >> reg = <1>;
> > > >> remote-endpoint = <&mixer1_out_tcon_top>;
> > > >>
> > > >> };
> > > >>
> > > >> tcon_top_in_tcon_tv: endpoint@2 {
> > > >>
> > > >> reg = <2>;
> > > >> // here is HDMI input connection, part of
> > > >> board DTS
> > > >> remote-endpoint = <board specific phandle
> > > >> to TV TCON output>;
> > > >>
> > > >> };
> > > >>
> > > >> };
> > > >>
> > > >> tcon_top_out: port@1 {
> > > >>
> > > >> #address-cells = <1>;
> > > >> #size-cells = <0>;
> > > >> reg = <1>;
> > > >>
> > > >> tcon_top_out_tcon0: endpoint@0 {
> > > >>
> > > >> reg = <0>;
> > > >> // here is mixer0 output connection, part
> > > >> of board DTS
> > > >> remote-endpoint = <board specific phandle
> > > >> to TCON>;
> > > >>
> > > >> };
> > > >>
> > > >> tcon_top_out_tcon1: endpoint@1 {
> > > >>
> > > >> reg = <1>;
> > > >> // here is mixer1 output connection, part
> > > >> of board DTS
> > > >> remote-endpoint = <board specific phandle
> > > >> to TCON>;
> > > >>
> > > >> };
> > > >>
> > > >> tcon_top_out_hdmi: endpoint@2 {
> > > >>
> > > >> reg = <2>;
> > > >> remote-endpoint = <&hdmi_in_tcon_top>;
> > > >>
> > > >> };
> > > >>
> > > >> };
> > > >>
> > > >> };
> > > >>
> > > >> };
> > > >
> > > > IIRC, each port is supposed to be one route for the data, so we would
> > > > have multiple ports, one for the mixers in input and for the tcon in
> > > > output, and one for the TCON in input and for the HDMI/TV in
> > > > output. Rob might correct me here.
>
> Ok, that seems more clean approach. I'll have to extend graph traversing
> algorithm in sun4i_drv.c, but that's no problem.
>
> Just to be clear, you have in mind 3 pairs of ports (0/1 for mixer0 mux, 2/3
> for mixer1 and 4/5 for HDMI input), right? That way each mux is represented
> with one pair of ports, even numbered for input and odd numbered for output.

Yep, unless Rob feels otherwise.

Maxime

--
Maxime Ripard, Bootlin (formerly Free Electrons)
Embedded Linux and Kernel engineering
https://bootlin.com

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