linux-kernel - [PATCH v2 2/5] drm/panel-simple: Don't wait longer for HPD than hpd_absent

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Date:   Fri, 15 Jan 2021 14:44:17 -0800
From:   Douglas Anderson <dianders@...omium.org>
To:     Thierry Reding <thierry.reding@...il.com>,
        Sam Ravnborg <sam@...nborg.org>
Cc:     Rob Clark <robdclark@...omium.org>,
        Stephen Boyd <swboyd@...omium.org>,
        Douglas Anderson <dianders@...omium.org>,
        Daniel Vetter <daniel@...ll.ch>,
        David Airlie <airlied@...ux.ie>,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: [PATCH v2 2/5] drm/panel-simple: Don't wait longer for HPD than hpd_absent_delay

If a panel has an hpd_absent_delay specified then we know exactly how
long the maximum time is before HPD must be asserted.  That means we
can use it as a timeout for polling the HPD pin instead of using an
arbitrary timeout.  This is especially useful for dealing with panels
that periodically fail to power on and need to be retried.  We can
detect the problem sooner.

Signed-off-by: Douglas Anderson <dianders@...omium.org>
---

Changes in v2:
- ("drm/panel-simple: Don't wait longer for HPD...") new for v2.

 drivers/gpu/drm/panel/panel-simple.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/panel/panel-simple.c b/drivers/gpu/drm/panel/panel-simple.c
index 581ab6810b70..30842cf6d414 100644
--- a/drivers/gpu/drm/panel/panel-simple.c
+++ b/drivers/gpu/drm/panel/panel-simple.c
@@ -382,6 +382,7 @@ static int panel_simple_prepare(struct drm_panel *panel)
 	unsigned int delay;
 	int err;
 	int hpd_asserted;
+	unsigned long hpd_wait_us;
 
 	if (p->prepared_time != 0)
 		return 0;
@@ -409,9 +410,14 @@ static int panel_simple_prepare(struct drm_panel *panel)
 				goto error;
 		}
 
+		if (p->desc->delay.hpd_absent_delay)
+			hpd_wait_us = p->desc->delay.hpd_absent_delay * 1000UL;
+		else
+			hpd_wait_us = 2000000;
+
 		err = readx_poll_timeout(gpiod_get_value_cansleep, p->hpd_gpio,
 					 hpd_asserted, hpd_asserted,
-					 1000, 2000000);
+					 1000, hpd_wait_us);
 		if (hpd_asserted < 0)
 			err = hpd_asserted;
 
-- 
2.30.0.284.gd98b1dd5eaa7-goog