[Intel-gfx] [v2] drm/i915/pps: improve eDP power on flow

[Lee Shawn C]

A panel power off cycle delay always append before turn eDP on.
Driver should check last_power_on and last_backlight_off before
insert this delay. If these values are the same, it means eDP
was off until now and driver can bypass power off cycle delay
to save some times to speed up eDP power on sequence.

v2: fix commit messages

Cc: Shankar Uma <uma.shankar at intel.com>
Cc: Jani Nikula <jani.nikula at linux.intel.com>
Cc: Ville Syrjälä <ville.syrjala at linux.intel.com>
Signed-off-by: Lee Shawn C <shawn.c.lee at intel.com>
---
 drivers/gpu/drm/i915/display/intel_pps.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/i915/display/intel_pps.c b/drivers/gpu/drm/i915/display/intel_pps.c
index 21944f5bf3a8..290473ec70d5 100644
--- a/drivers/gpu/drm/i915/display/intel_pps.c
+++ b/drivers/gpu/drm/i915/display/intel_pps.c
@@ -509,6 +509,13 @@ static void wait_panel_power_cycle(struct intel_dp *intel_dp)
 	ktime_t panel_power_on_time;
 	s64 panel_power_off_duration;
 
+	/* When last_power_on equal to last_backlight_off, it means driver did not
+	 * turn on or off eDP panel so far. So we can bypass power cycle delay to
+	 * save some times here.
+	 */
+	if (intel_dp->pps.last_power_on == intel_dp->pps.last_backlight_off)
+		return;
+
 	drm_dbg_kms(&i915->drm, "Wait for panel power cycle\n");
 
 	/* take the difference of current time and panel power off time
@@ -1100,7 +1107,7 @@ static void pps_init_timestamps(struct intel_dp *intel_dp)
 {
 	intel_dp->pps.panel_power_off_time = ktime_get_boottime();
 	intel_dp->pps.last_power_on = jiffies;
-	intel_dp->pps.last_backlight_off = jiffies;
+	intel_dp->pps.last_backlight_off = intel_dp->pps.last_power_on;
 }
 
 static void
-- 
2.17.1