linux-kernel - Re: [PATCH v6 1/8] drm/msm/dp: Add eDP support via aux

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Date:   Fri, 8 Apr 2022 15:19:59 +0300
From:   Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
To:     Doug Anderson <dianders@...omium.org>
Cc:     Abhinav Kumar <quic_abhinavk@...cinc.com>,
        "Sankeerth Billakanti (QUIC)" <quic_sbillaka@...cinc.com>,
        quic_kalyant <quic_kalyant@...cinc.com>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>,
        quic_vproddut <quic_vproddut@...cinc.com>,
        David Airlie <airlied@...ux.ie>,
        linux-arm-msm <linux-arm-msm@...r.kernel.org>,
        "Kuogee Hsieh (QUIC)" <quic_khsieh@...cinc.com>,
        freedreno <freedreno@...ts.freedesktop.org>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        "bjorn.andersson@...aro.org" <bjorn.andersson@...aro.org>,
        Sean Paul <seanpaul@...omium.org>,
        "Aravind Venkateswaran (QUIC)" <quic_aravindh@...cinc.com>,
        Stephen Boyd <swboyd@...omium.org>,
        Sean Paul <sean@...rly.run>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v6 1/8] drm/msm/dp: Add eDP support via aux_bus

On Fri, 8 Apr 2022 at 03:26, Doug Anderson <dianders@...omium.org> wrote:
>
> Hi,
>
> On Thu, Apr 7, 2022 at 4:46 PM Dmitry Baryshkov
> <dmitry.baryshkov@...aro.org> wrote:
> >
> > > The way I'm arguing it should work is that:
> > >
> > > 1. A whole bunch of the DP init code should move to the DP driver's
> > > probe function. This includes parsing the DT, acquiring clocks,
> > > getting a handle to our PHY, and IO mapping registers. As far as I
> > > know, there's no reason to wait on all the components being probed in
> > > order to do this stuff.
> >
> > Yes. And that's one of the reasons I tried to stay away from the DP
> > driver. Each time I open the source code, my hands itch to start
> > refactoring the code.
> >
> > >
> > > 2. Once we have done the above things, it should be possible to do AUX
> > > transfers, correct? ...and then we can populate the AUX bus from the
> > > probe function too.
> >
> > No. In the DP case the AUX bus is inaccessible until the dongle is
> > plugged (see all the HPD handling, phy_init()/phy_power_on() is hidden
> > somewhere in that path)
>
> I guess my thought was that in DP you could still create the AUX bus
> at probe time. Then for DP you just return an instant "transfer
> failed" from the AUX bus if HPD isn't asserted. For eDP (as discussed
> elsewhere) when we try to do an AUX transfer then we delay until HPD
> is there.

I think panel-edp would already handle the delay, so we do not need to
have this logic in the DP driver.

> So we can still acquire resources (clocks, PHY, io maps, etc) at probe
> time for DP and create the AUX bus, right? It will just return
> "-ENODEV" if HPD isn't asserted and you're DP?

Yes, please. I still suppose that we'd need a separate case to
power_on eDP's PHY during the probe time. Maybe I'm mistaken here.

-- 
With best wishes
Dmitry