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

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Date:   Fri, 1 Oct 2021 14:02:25 -0700
From:   Bjorn Andersson <bjorn.andersson@...aro.org>
To:     Doug Anderson <dianders@...omium.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

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.

So I picked 2, because I'm not able to figure out a way to distinguish
between a not yet probed panel and the USB-C controller...

Any suggestions?

Regards,
Bjorn