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:   Sat, 16 Apr 2022 03:14:42 +0300
From:   Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
To:     Doug Anderson <dianders@...omium.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

On 16/04/2022 03:12, Doug Anderson wrote:
> Hi,
> 
> On Fri, Apr 15, 2022 at 3:12 PM Dmitry Baryshkov
> <dmitry.baryshkov@...aro.org> wrote:
>>
>> On Sat, 16 Apr 2022 at 00:17, Doug Anderson <dianders@...omium.org> wrote:
>>>
>>> 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.
>>
>> 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.


-- 
With best wishes
Dmitry