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From:   Chen-Yu Tsai <wens@csie.org>
Date:   Fri, 1 Jun 2018 09:19:43 -0700
Message-ID: <CAGb2v667pdjfHXYpBk1ER5sC8vgpcaOFKEbEByWoD1zh9Z0cyg@mail.gmail.com>
Subject: Re: [PATCH 06/15] drm/sun4i: tcon: Add support for tcon-top
To:     Maxime Ripard <maxime.ripard@bootlin.com>
Cc:     =?UTF-8?Q?Jernej_=C5=A0krabec?= <jernej.skrabec@siol.net>,
        Rob Herring <robh+dt@kernel.org>,
        Mark Rutland <mark.rutland@arm.com>,
        dri-devel <dri-devel@lists.freedesktop.org>,
        devicetree <devicetree@vger.kernel.org>,
        linux-arm-kernel <linux-arm-kernel@lists.infradead.org>,
        linux-kernel <linux-kernel@vger.kernel.org>,
        linux-clk <linux-clk@vger.kernel.org>,
        linux-sunxi <linux-sunxi@googlegroups.com>
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On Fri, Jun 1, 2018 at 8:29 AM, Maxime Ripard <maxime.ripard@bootlin.com> wrote:
> On Thu, May 31, 2018 at 07:54:08PM +0200, Jernej Škrabec wrote:
>> Dne četrtek, 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.
>
>> tcon_tv0: lcd-controller@1c73000 {
>>       compatible = "allwinner,sun8i-r40-tcon-tv-0";
>>       ...
>>       ports {
>>               #address-cells = <1>;
>>               #size-cells = <0>;
>>
>>               tcon_tv0_in: port@0 {
>>                       reg = <0>;
>>
>>                       tcon_tv0_in_tcon_top: endpoint {
>>                               // endpoint depends on board, part of board DTS
>>                               remote-endpoint = <phandle to one of tcon_top_out_tcon>;
>
> Just curious, what would be there?
>
>>                       };
>>               };
>>
>>               tcon_tv0_out: port@1 {
>>                       #address-cells = <1>;
>>                       #size-cells = <0>;
>>                       reg = <1>;
>>
>>                       // endpoints to TV TOP and TCON TOP HDMI input
>>                       ...
>>               };
>>       };
>> };
>>
>> tcon_tv1: lcd-controller@1c74000 {
>>       compatible = "allwinner,sun8i-r40-tcon-tv-1";
>>       ...
>>       ports {
>>               #address-cells = <1>;
>>               #size-cells = <0>;
>>
>>               tcon_tv1_in: port@0 {
>>                       reg = <0>;
>>
>>                       tcon_tv1_in_tcon_top: endpoint {
>>                               // endpoint depends on board, part of board DTS
>>                               remote-endpoint = <phandle to one of tcon_top_out_tcon>;
>>                       };
>>               };
>>
>>               tcon_tv1_out: port@1 {
>>                       #address-cells = <1>;
>>                       #size-cells = <0>;
>>                       reg = <1>;
>>
>>                       // endpoints to TV TOP and TCON TOP HDMI input
>>                       ...
>>               };
>>       };
>> };
>>
>> tcon_lcd0 and tcon_lcd1 would have similar connections, except that for
>> outputs would be LCD or LVDS panels or MIPI DSI encoder.
>>
>> Please note that each TCON (there are 4 of them) would need to have unique
>> compatible and have HW index stored in quirks data. It would be used by TCON
>> TOP driver for configuring muxes.
>
> Can't we use the port/endpoint ID instead? If the mux is the only
> thing that changes, the compatible has no reason to. It's the same IP,
> and the only thing that changes is something that is not part of that
> IP.

I agree. Endpoint IDs should provide that information. I'm still not
sure How to encode multiple in/out mux groups in a device node though.

ChenYu