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

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Message-ID: <MW4PR02MB71866443CD6174EFCF57251BE1E69@MW4PR02MB7186.namprd02.prod.outlook.com>
Date:   Thu, 7 Apr 2022 12:41:35 +0000
From:   "Sankeerth Billakanti (QUIC)" <quic_sbillaka@...cinc.com>
To:     "dmitry.baryshkov@...aro.org" <dmitry.baryshkov@...aro.org>,
        "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 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.
> 

Okay. Will add it.

> --
> With best wishes
> Dmitry