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

From: Doug Anderson <dianders@chromium.org>
To: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Cc: Sankeerth Billakanti <quic_sbillaka@quicinc.com>,
	Philip Chen <philipchen@chromium.org>,
	David Airlie <airlied@linux.ie>,
	LKML <linux-kernel@vger.kernel.org>,
	Abhinav Kumar <quic_abhinavk@quicinc.com>,
	Robert Foss <robert.foss@linaro.org>,
	Stephen Boyd <swboyd@chromium.org>,
	Thierry Reding <thierry.reding@gmail.com>,
	dri-devel <dri-devel@lists.freedesktop.org>,
	Hsin-Yi Wang <hsinyi@chromium.org>,
	Sam Ravnborg <sam@ravnborg.org>
Subject: Re: [RFC PATCH 4/6] drm/panel-edp: Take advantage of is_hpd_asserted() in struct drm_dp_aux
Date: Mon, 18 Apr 2022 10:18:54 -0700	[thread overview]
Message-ID: <CAD=FV=VP+tcrCwBQeF+QTBcsTraZVzxQqnAKBQQ_Hb6CyUQ0BA@mail.gmail.com> (raw)
In-Reply-To: <835fa3cd-0777-1dea-972f-3e24d5aeda3a@linaro.org>

Hi,

On Fri, Apr 15, 2022 at 5:14 PM Dmitry Baryshkov
<dmitry.baryshkov@linaro.org> wrote:
>
> On 16/04/2022 03:12, Doug Anderson wrote:
> > Hi,
> >
> > On Fri, Apr 15, 2022 at 3:12 PM Dmitry Baryshkov
> > <dmitry.baryshkov@linaro.org> wrote:
> >>
> >> On Sat, 16 Apr 2022 at 00:17, Doug Anderson <dianders@chromium.org> wrote:
> >>>
> >>> Hi,
> >>>
> >>> On Thu, Apr 14, 2022 at 5:51 PM Dmitry Baryshkov
> >>> <dmitry.baryshkov@linaro.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@chromium.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@linaro.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.
> >>
> >> This might work. Can you check it, please?
> >
> > Cool. I'll spin with this. Hopefully early next week unless my inbox
> > blows up. ...or my main PC's SSD like happened this week. ;-)
> >
> >
> >> BTW: are these changes dependent on the first part of the patchset? It
> >> might be worth splitting the patchset into two parts.
> >
> > Definitely not. As per the cover letter, this is two series jammed
> > into one. I'm happy to split them up. The 2nd half seems much less
> > controversial.
>
> Great, let's get it in then. As you have time.

Breadcrumbs: I've posted this as:

https://lore.kernel.org/r/20220418171757.2282651-1-dianders@chromium.org

-Doug