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

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Date:   Mon, 30 Aug 2021 09:01:58 -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 Sat, Aug 28, 2021 at 7:40 AM Bjorn Andersson
<bjorn.andersson@...aro.org> wrote:
>
> On Fri 27 Aug 15:52 CDT 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?
> >
>
> I thought port 1 was the link to the Type-C controller, didn't give it a
> second thought and took the next available.
>
> But per the binding it makes sense that the panel is the "Output
> endpoint of the controller" and I guess one will have either a Type-C
> controller or a panel - even after the DP rework?

Right, my understanding is that "port 1" is the output port
irregardless of whether you're outputting to a panel or a DP
connector. I think the only case it would make sense to add a new port
is if it was possible for the output to be connected to both a panel
and a DP port simultaneously. ...but that doesn't make sense.

-Doug