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 03:51:00 +0300
From:   Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
To:     Douglas Anderson <dianders@...omium.org>,
        dri-devel@...ts.freedesktop.org
Cc:     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>,
        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 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>


> +
> +		err = readx_poll_timeout(panel_edp_read_hpd, p,
>   					 hpd_asserted, hpd_asserted,
>   					 1000, hpd_wait_us);
>   		if (hpd_asserted < 0)
> @@ -532,18 +553,22 @@ static int panel_edp_enable(struct drm_panel *panel)
>   	/*
>   	 * If there is a "prepare_to_enable" delay then that's supposed to be
>   	 * the delay from HPD going high until we can turn the backlight on.
> -	 * However, we can only count this if HPD is handled by the panel
> -	 * driver, not if it goes to a dedicated pin on the controller.
> +	 * However, we can only count this if HPD is readable by the panel
> +	 * driver.
> +	 *
>   	 * If we aren't handling the HPD pin ourselves then the best we
>   	 * can do is assume that HPD went high immediately before we were
> -	 * called (and link training took zero time).
> +	 * called (and link training took zero time). Note that "no-hpd"
> +	 * actually counts as handling HPD ourselves since we're doing the
> +	 * worst case delay (in prepare) ourselves.
>   	 *
>   	 * NOTE: if we ever end up in this "if" statement then we're
>   	 * guaranteed that the panel_edp_wait() call below will do no delay.
>   	 * It already handles that case, though, so we don't need any special
>   	 * code for it.
>   	 */
> -	if (p->desc->delay.prepare_to_enable && !p->hpd_gpio && !p->no_hpd)
> +	if (p->desc->delay.prepare_to_enable &&
> +	    !panel_edp_can_read_hpd(p) && !p->no_hpd)
>   		delay = max(delay, p->desc->delay.prepare_to_enable);
>   
>   	if (delay)


-- 
With best wishes
Dmitry