linux-kernel - Re: [PATCH v1 1/2] drm/msm/dp: enable HDP plugin/unplugged interrupts to hpd

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Message-ID: <CAE-0n51SHQhUJiY=BJp8CQQ1aTAOxeMDr2+NX_vpmjN_cyJJrA@mail.gmail.com>
Date:   Fri, 12 May 2023 11:03:07 -0700
From:   Stephen Boyd <swboyd@...omium.org>
To:     Dmitry Baryshkov <dmitry.baryshkov@...aro.org>,
        Kuogee Hsieh <quic_khsieh@...cinc.com>
Cc:     Bjorn Andersson <andersson@...nel.org>,
        dri-devel@...ts.freedesktop.org, robdclark@...il.com,
        sean@...rly.run, dianders@...omium.org, vkoul@...nel.org,
        daniel@...ll.ch, airlied@...il.com, agross@...nel.org,
        quic_abhinavk@...cinc.com, quic_jesszhan@...cinc.com,
        quic_sbillaka@...cinc.com, marijn.suijten@...ainline.org,
        freedreno@...ts.freedesktop.org, linux-arm-msm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1 1/2] drm/msm/dp: enable HDP plugin/unplugged interrupts
 to hpd_enable/disable

Quoting Dmitry Baryshkov (2023-05-11 17:54:19)
> On Fri, 12 May 2023 at 03:16, Kuogee Hsieh <quic_khsieh@...cinc.com> wrote:
> > 1) DP with GPIO: No downstream drm_bridge are connected, is_edp = false
> > and internal HPD-logic is in used (internal_hpd = true). Power needs to
> > be on at all times etc.
> >
> > 2) DP without GPIO: Downstream drm_bridge connected, is_edp = false and
> > internal HPD-logic should not be used/enabled (internal_hpd = false).
> > Power doesn't need to be on unless hpd_notify is invoked to tell us that
> > there's something connected...
> >
> > - dp_bridge_hpd_notify(). What is the point of this check? <== i have
> > below two questions,
> >
> > 1) can you explain when/what this dp_bridge_hpd_notify() will be called?
>
> The call chain is drm_bridge_hpd_notify() ->
> drm_bridge_connector_hpd_notify() -> .hpd_notify() for all drm_bridge
> in chain
>
> One should add a call to drm_bridge_hpd_notify() when the hotplug
> event has been detected.
>
> Also please note the patch https://patchwork.freedesktop.org/patch/484432/
>
> >
> > 2) is dp_bridge_hpd_notify() only will be called at above case #2? and
> > it will not be used by case #1?
>
> Once the driver calls drm_bridge_hpd_notify() in the hpd path, the
> hpd_notify callbacks will be called in case#1 too.
>
> BTW: I don't see drm_bridge_hpd_notify() or
> drm_kms_{,connector_}_hotplug_event() HPD notifications in the DP
> driver at all. This should be fixed.
>

Is dp_bridge_hpd_notify() being called by
drm_helper_probe_single_connector_modes() when the connectors are
detected?

I see drm_helper_probe_detect() calls connector->funcs->detect() which I
think calls
drm_bridge_connector_funcs::drm_bridge_connector_hpd_notify() but I
haven't confirmed yet. The 'detect' bridge is the DP bridge in msm
driver

         if (!dp_display->is_edp) {
                bridge->ops =
                        DRM_BRIDGE_OP_DETECT |

so if the bridge_connector is being used then I think when fill_modes()
is called we'll run the detect cycle and call the hpd_notify callbacks
on the bridge chain.