linux-kernel - Re: [RFC] drm/msm/dp: Allow attaching a drm

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Date:   Mon, 4 Oct 2021 17:36:10 -0700
From:   Doug Anderson <dianders@...omium.org>
To:     Bjorn Andersson <bjorn.andersson@...aro.org>
Cc:     Rob Clark <robdclark@...il.com>, Sean Paul <sean@...rly.run>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        linux-arm-msm <linux-arm-msm@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Abhinav Kumar <abhinavk@...eaurora.org>,
        Stephen Boyd <swboyd@...omium.org>,
        Kuogee Hsieh <khsieh@...eaurora.org>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        Vara Reddy <varar@...eaurora.org>,
        freedreno <freedreno@...ts.freedesktop.org>,
        Chandan Uddaraju <chandanu@...eaurora.org>
Subject: Re: [RFC] drm/msm/dp: Allow attaching a drm_panel

Hi,

On Fri, Oct 1, 2021 at 2:00 PM Bjorn Andersson
<bjorn.andersson@...aro.org> wrote:
>
> On Fri 27 Aug 13:52 PDT 2021, Doug Anderson wrote:
>
> > Hi,
> >
> > On Mon, Jul 26, 2021 at 4:15 PM Bjorn Andersson
> > <bjorn.andersson@...aro.org> wrote:
> > >
> > > +static int dp_parser_find_panel(struct dp_parser *parser)
> > > +{
> > > +       struct device_node *np = parser->pdev->dev.of_node;
> > > +       int rc;
> > > +
> > > +       rc = drm_of_find_panel_or_bridge(np, 2, 0, &parser->drm_panel, NULL);
> >
> > Why port 2? Shouldn't this just be port 1 always? The yaml says that
> > port 1 is "Output endpoint of the controller". We should just use port
> > 1 here, right?
> >
>
> Finally got back to this, changed it to 1 and figured out why I left it
> at 2.
>
> drm_of_find_panel_or_bridge() on a DP controller will find the of_graph
> reference to the USB-C controller, scan through the registered panels
> and conclude that the of_node of the USB-C controller isn't a registered
> panel and return -EPROBE_DEFER.

I'm confused, but maybe it would help if I could see something
concrete. Is there a specific board this was happening on?

Under the DP node in the device tree I expect:

ports {
  port@1 {
    reg = <1>;
    edp_out: endpoint {
      remote-endpoint = <&edp_panel_in>;
    };
  };
};

If you have "port@1" pointing to a USB-C controller but this instance
of the DP controller is actually hooked up straight to a panel then
you should simply delete the "port@1" that points to the typeC and
replace it with one that points to a panel, right?

-Doug