linux-kernel - Re: [RFC PATCH 4/6] drm/panel-edp: Take advantage of is_hpd_asserted() in struct drm_dp

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Date:   Fri, 15 Apr 2022 14:17:24 -0700
From:   Doug Anderson <dianders@...omium.org>
To:     Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
Cc:     dri-devel <dri-devel@...ts.freedesktop.org>,
        Robert Foss <robert.foss@...aro.org>,
        Hsin-Yi Wang <hsinyi@...omium.org>,
        Abhinav Kumar <quic_abhinavk@...cinc.com>,
        Sankeerth Billakanti <quic_sbillaka@...cinc.com>,
        Philip Chen <philipchen@...omium.org>,
        Stephen Boyd <swboyd@...omium.org>,
        Daniel Vetter <daniel@...ll.ch>,
        David Airlie <airlied@...ux.ie>,
        Sam Ravnborg <sam@...nborg.org>,
        Thierry Reding <thierry.reding@...il.com>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH 4/6] drm/panel-edp: Take advantage of
 is_hpd_asserted() in struct drm_dp_aux

Hi,

On Thu, Apr 14, 2022 at 5:51 PM Dmitry Baryshkov
<dmitry.baryshkov@...aro.org> wrote:
>
> On 09/04/2022 05:36, Douglas Anderson wrote:
> > Let's add support for being able to read the HPD pin even if it's
> > hooked directly to the controller. This will allow us to get more
> > accurate delays also lets us take away the waiting in the AUX transfer
> > functions of the eDP controller drivers.
> >
> > Signed-off-by: Douglas Anderson <dianders@...omium.org>
> > ---
> >
> >   drivers/gpu/drm/panel/panel-edp.c | 37 ++++++++++++++++++++++++++-----
> >   1 file changed, 31 insertions(+), 6 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/panel/panel-edp.c b/drivers/gpu/drm/panel/panel-edp.c
> > index 1732b4f56e38..4a143eb9544b 100644
> > --- a/drivers/gpu/drm/panel/panel-edp.c
> > +++ b/drivers/gpu/drm/panel/panel-edp.c
> > @@ -417,6 +417,19 @@ static int panel_edp_get_hpd_gpio(struct device *dev, struct panel_edp *p)
> >       return 0;
> >   }
> >
> > +static bool panel_edp_can_read_hpd(struct panel_edp *p)
> > +{
> > +     return !p->no_hpd && (p->hpd_gpio || (p->aux && p->aux->is_hpd_asserted));
> > +}
> > +
> > +static bool panel_edp_read_hpd(struct panel_edp *p)
> > +{
> > +     if (p->hpd_gpio)
> > +             return gpiod_get_value_cansleep(p->hpd_gpio);
> > +
> > +     return p->aux->is_hpd_asserted(p->aux);
> > +}
> > +
> >   static int panel_edp_prepare_once(struct panel_edp *p)
> >   {
> >       struct device *dev = p->base.dev;
> > @@ -441,13 +454,21 @@ static int panel_edp_prepare_once(struct panel_edp *p)
> >       if (delay)
> >               msleep(delay);
> >
> > -     if (p->hpd_gpio) {
> > +     if (panel_edp_can_read_hpd(p)) {
> >               if (p->desc->delay.hpd_absent)
> >                       hpd_wait_us = p->desc->delay.hpd_absent * 1000UL;
> >               else
> >                       hpd_wait_us = 2000000;
> >
> > -             err = readx_poll_timeout(gpiod_get_value_cansleep, p->hpd_gpio,
> > +             /*
> > +              * Extra max delay, mostly to account for ps8640. ps8640
> > +              * is crazy and the bridge chip driver itself has over 200 ms
> > +              * of delay if it needs to do the pm_runtime resume of the
> > +              * bridge chip to read the HPD.
> > +              */
> > +             hpd_wait_us += 3000000;
>
> I think this should come in a separate commit and ideally this should be
> configurable somehow. Other hosts wouldn't need such 'additional' delay.
>
> With this change removed:
>
> Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>

What would you think about changing the API slightly? Instead of
is_hpd_asserted(), we change it to wait_hpd_asserted() and it takes a
timeout in microseconds. If you pass 0 for the timeout the function is
defined to behave the same as is_hpd_asserted() today--AKA a single
poll of the line.

-Doug