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

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Date:   Mon, 4 Apr 2022 18:32:25 +0000
From:   "Sankeerth Billakanti (QUIC)" <quic_sbillaka@...cinc.com>
To:     Doug Anderson <dianders@...omium.org>,
        "Sankeerth Billakanti (QUIC)" <quic_sbillaka@...cinc.com>
CC:     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>,
        "dmitry.baryshkov@...aro.org" <dmitry.baryshkov@...aro.org>,
        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

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.

> 
> -Doug

Thank you,
Sankeerth