linux-kernel - Re: [PATCH v6 7/8] drm/msm/dp: Support edp/dp without hpd

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Date:   Tue, 5 Apr 2022 00:15:16 +0300
From:   Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
To:     "Sankeerth Billakanti (QUIC)" <quic_sbillaka@...cinc.com>
Cc:     Doug Anderson <dianders@...omium.org>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        linux-arm-msm <linux-arm-msm@...r.kernel.org>,
        freedreno <freedreno@...ts.freedesktop.org>,
        LKML <linux-kernel@...r.kernel.org>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>, Rob Clark <robdclark@...il.com>,
        Sean Paul <seanpaul@...omium.org>,
        Stephen Boyd <swboyd@...omium.org>,
        quic_kalyant <quic_kalyant@...cinc.com>,
        "Abhinav Kumar (QUIC)" <quic_abhinavk@...cinc.com>,
        "Kuogee Hsieh (QUIC)" <quic_khsieh@...cinc.com>,
        "bjorn.andersson@...aro.org" <bjorn.andersson@...aro.org>,
        Sean Paul <sean@...rly.run>, David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        quic_vproddut <quic_vproddut@...cinc.com>,
        "Aravind Venkateswaran (QUIC)" <quic_aravindh@...cinc.com>
Subject: Re: [PATCH v6 7/8] drm/msm/dp: Support edp/dp without hpd

On Mon, 4 Apr 2022 at 21:32, Sankeerth Billakanti (QUIC)
<quic_sbillaka@...cinc.com> wrote:
>
> Hi Doug,
>
> > On Wed, Mar 30, 2022 at 9:04 AM Sankeerth Billakanti
> > <quic_sbillaka@...cinc.com> wrote:
> > >
> > > Some eDP sinks or platform boards will not support hpd.
> > > This patch adds support for those cases.
> >
> > You could say more, like:
> >
> > If we're not using HPD then _both_ the panel node and the eDP controller
> > node will have "no-hpd". This tells the eDP panel code to hardcode the
> > maximum possible delay for a panel to power up and tells the eDP driver that
> > it should continue to do transfers even if HPD isn't asserted.
> >
>
> Okay. I will add it
>
> >
> > > Signed-off-by: Sankeerth Billakanti <quic_sbillaka@...cinc.com>
> > > ---
> > >  drivers/gpu/drm/msm/dp/dp_catalog.c | 15 ++++++++++++---
> > >  1 file changed, 12 insertions(+), 3 deletions(-)
> > >
> > > diff --git a/drivers/gpu/drm/msm/dp/dp_catalog.c
> > > b/drivers/gpu/drm/msm/dp/dp_catalog.c
> > > index 1809ce2..8f1fc71 100644
> > > --- a/drivers/gpu/drm/msm/dp/dp_catalog.c
> > > +++ b/drivers/gpu/drm/msm/dp/dp_catalog.c
> > > @@ -244,10 +244,17 @@ void dp_catalog_aux_update_cfg(struct
> > dp_catalog
> > > *dp_catalog)
> > >
> > >  int dp_catalog_aux_wait_for_hpd_connect_state(struct dp_catalog
> > > *dp_catalog)  {
> > > -       u32 state;
> > > +       u32 state, hpd_en;
> > >         struct dp_catalog_private *catalog = container_of(dp_catalog,
> > >                                 struct dp_catalog_private,
> > > dp_catalog);
> > >
> > > +       hpd_en = dp_read_aux(catalog, REG_DP_DP_HPD_CTRL);
> > > +       hpd_en &= DP_DP_HPD_CTRL_HPD_EN;
> > > +
> > > +       /* no-hpd case */
> > > +       if (!hpd_en)
> > > +               return 0;
> > > +
> > >         /* poll for hpd connected status every 2ms and timeout after 500ms */
> > >         return readl_poll_timeout(catalog->io->dp_controller.aux.base +
> > >                                 REG_DP_DP_HPD_INT_STATUS, @@ -586,8
> > > +593,10 @@ void dp_catalog_ctrl_hpd_config(struct dp_catalog
> > *dp_catalog)
> > >         reftimer |= DP_DP_HPD_REFTIMER_ENABLE;
> > >         dp_write_aux(catalog, REG_DP_DP_HPD_REFTIMER, reftimer);
> > >
> > > -       /* Enable HPD */
> > > -       dp_write_aux(catalog, REG_DP_DP_HPD_CTRL,
> > DP_DP_HPD_CTRL_HPD_EN);
> > > +       /* Enable HPD if supported*/
> > > +       if (!of_property_read_bool(catalog->dev->of_node, "no-hpd"))
> >
> > I don't think this is a particularly lightweight operation. It's literally iterating
> > through all of our device tree properties and doing string compares on them.
> > ...but this function is called somewhat often, isn't it? It feels like the kind of
> > thing that should happen at probe time and be stored in a boolean.
> >
> > ...and then you can use that same boolean in
> > dp_catalog_aux_wait_for_hpd_connect_state() rather than reading the
> > register value, right?
> >
> It is called twice for DP. Once while booting through a thread scheduled from kms_obj_init
> and when resuming from PM suspend.
>
> With aux_bus addition, this function will be called thrice for eDP. Once during bootup with
> aux_bus, then from scheduled event from kms_obj_init and pm resume like DP.
>
> I will check if we can use a no-hpd Boolean flag instead.

As the driver has a separate dp_parser code, it might be a good fit to
parse the DT once and then to use boolean flag afterwards.

-- 
With best wishes
Dmitry