linux-kernel - Re: [PATCH v3 2/4] drm/panel-edp: Take advantage of wait_hpd_asserted() in struct drm_dp

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Date:   Tue, 14 Jun 2022 14:57:52 -0700
From:   Doug Anderson <dianders@...omium.org>
To:     Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
Cc:     dri-devel <dri-devel@...ts.freedesktop.org>,
        Hsin-Yi Wang <hsinyi@...omium.org>,
        Sankeerth Billakanti <quic_sbillaka@...cinc.com>,
        Philip Chen <philipchen@...omium.org>,
        Robert Foss <robert.foss@...aro.org>,
        Stephen Boyd <swboyd@...omium.org>,
        Abhinav Kumar <quic_abhinavk@...cinc.com>,
        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: [PATCH v3 2/4] drm/panel-edp: Take advantage of
 wait_hpd_asserted() in struct drm_dp_aux

Hi,

On Thu, Jun 2, 2022 at 8:12 AM Dmitry Baryshkov
<dmitry.baryshkov@...aro.org> wrote:
>
> On 18/04/2022 20:17, 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>
>
> Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
>
> > ---
> >
> > (no changes since v2)
> >
> > Changes in v2:
> > - Change is_hpd_asserted() to wait_hpd_asserted()
> >
> >   drivers/gpu/drm/panel/panel-edp.c | 33 +++++++++++++++++++++----------
> >   1 file changed, 23 insertions(+), 10 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/panel/panel-edp.c b/drivers/gpu/drm/panel/panel-edp.c
> > index 1732b4f56e38..086e0bf52fb9 100644
> > --- a/drivers/gpu/drm/panel/panel-edp.c
> > +++ b/drivers/gpu/drm/panel/panel-edp.c
> > @@ -417,6 +417,11 @@ 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->wait_hpd_asserted));
> > +}
> > +
> >   static int panel_edp_prepare_once(struct panel_edp *p)
> >   {
> >       struct device *dev = p->base.dev;
> > @@ -441,17 +446,21 @@ 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,
> > -                                      hpd_asserted, hpd_asserted,
> > -                                      1000, hpd_wait_us);
> > -             if (hpd_asserted < 0)
> > -                     err = hpd_asserted;
> > +             if (p->hpd_gpio) {
> > +                     err = readx_poll_timeout(gpiod_get_value_cansleep,
> > +                                              p->hpd_gpio, hpd_asserted,
> > +                                              hpd_asserted, 1000, hpd_wait_us);
> > +                     if (hpd_asserted < 0)
> > +                             err = hpd_asserted;
> > +             } else {
> > +                     err = p->aux->wait_hpd_asserted(p->aux, hpd_wait_us);
> > +             }
>
> I'm close to thinking that this construct deserves a separate helper.

Just to close the loop: I didn't try to create a helper for v5. I'm
not completely convinced that this will be common. I would tend to
expect that having HPD handled by a GPIO is somewhat rare. It's also
fairly rare to have a panel that's not handled by the generic
panel-edp. We ended up with the GPIO on trogdor because of the weird
debouncing on sn85dsi86 and we ended up with one case of not using
edp-panel on trogdor because of the weird power sequencing of the
Samsung OLED panel that's on homestar.

I'd also note that the generic eDP panel has a special case for
"timeout" which we don't have on the Samsung panel to handle at least
one panel I found that sometimes simply didn't come up but then
_would_ come up on a retry...

That doesn't mean we couldn't abstract it out later, of course. ;-)

-Doug


-Doug