[Intel-gfx] [PATCH 2/6] drm/i915: save some time when waiting the eDP timings

[Paulo Zanoni]

From: Paulo Zanoni <paulo.r.zanoni at intel.com>

The eDP spec defines some points where after you do action A, you have
to wait some time before action B. The thing is that in our driver
action B does not happen exactly after action A, but we still use
msleep() calls directly. What this patch does is that we record the
timestamp of when action A happened, then, just before action B, we
look at how much time has passed and only sleep the remaining amount
needed.

With this change, I am able to save about 5-20ms (out of the total
200ms) of the backlight_off delay and completely skip the 1ms
backlight_on delay. The 600ms vdd_off delay doesn't happen during
normal usage anymore due to a previous patch.

v2: - Rename ironlake_wait_jiffies_delay to intel_wait_until_after and
      move it to intel_display.c
    - Fix the msleep call: diff is in jiffies
v3: - Use "tmp_jiffies" so we don't need to worry about the value of
      "jiffies" advancing while we're doing the math.
v4: - Rename function again.
    - Move function to i915_drv.h.
    - Store last_power_cycle at edp_panel_off too.
    - Use msecs_to_jiffies_timeout, then replace the msleep with an
      open-coded version that avoids the extra +1 jiffy.
    - Try to add units to every variable name so we don't confuse
      jiffies with milliseconds.

Signed-off-by: Paulo Zanoni <paulo.r.zanoni at intel.com>
---
 drivers/gpu/drm/i915/i915_drv.h  | 29 +++++++++++++++++++++++++++++
 drivers/gpu/drm/i915/intel_dp.c  | 27 ++++++++++++++++++++++++---
 drivers/gpu/drm/i915/intel_drv.h |  3 +++
 3 files changed, 56 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
index cc8afff..7e9b436 100644
--- a/drivers/gpu/drm/i915/i915_drv.h
+++ b/drivers/gpu/drm/i915/i915_drv.h
@@ -2636,4 +2636,33 @@ timespec_to_jiffies_timeout(const struct timespec *value)
 	return min_t(unsigned long, MAX_JIFFY_OFFSET, j + 1);
 }
 
+/*
+ * If you need to wait X milliseconds between events A and B, but event B
+ * doesn't happen exactly after event A, you record the timestamp (jiffies) of
+ * when event A happened, then just before event B you call this function and
+ * pass the timestamp as the first argument, and X as the second argument.
+ */
+static inline void
+wait_remaining_ms_from_jiffies(unsigned long timestamp_jiffies, int to_wait_ms)
+{
+	unsigned long target_jiffies, tmp_jiffies;
+	unsigned int remaining_ms;
+
+	/*
+	 * Don't re-read the value of "jiffies" every time since it may change
+	 * behind our back and break the math.
+	 */
+	tmp_jiffies = jiffies;
+	target_jiffies = timestamp_jiffies +
+			 msecs_to_jiffies_timeout(to_wait_ms);
+
+	if (time_after(target_jiffies, tmp_jiffies)) {
+		remaining_ms = jiffies_to_msecs((long)target_jiffies -
+						(long)tmp_jiffies);
+		while (remaining_ms)
+			remaining_ms =
+				schedule_timeout_uninterruptible(remaining_ms);
+	}
+}
+
 #endif
diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
index 9d96447..2f82af4 100644
--- a/drivers/gpu/drm/i915/intel_dp.c
+++ b/drivers/gpu/drm/i915/intel_dp.c
@@ -1057,9 +1057,26 @@ static void ironlake_wait_panel_off(struct intel_dp *intel_dp)
 static void ironlake_wait_panel_power_cycle(struct intel_dp *intel_dp)
 {
 	DRM_DEBUG_KMS("Wait for panel power cycle\n");
+
+	/* When we disable the VDD override bit last we have to do the manual
+	 * wait. */
+	wait_remaining_ms_from_jiffies(intel_dp->last_power_cycle,
+				       intel_dp->panel_power_cycle_delay);
+
 	ironlake_wait_panel_status(intel_dp, IDLE_CYCLE_MASK, IDLE_CYCLE_VALUE);
 }
 
+static void ironlake_wait_backlight_on(struct intel_dp *intel_dp)
+{
+	wait_remaining_ms_from_jiffies(intel_dp->last_power_on,
+				       intel_dp->backlight_on_delay);
+}
+
+static void ironlake_edp_wait_backlight_off(struct intel_dp *intel_dp)
+{
+	wait_remaining_ms_from_jiffies(intel_dp->last_backlight_off,
+				       intel_dp->backlight_off_delay);
+}
 
 /* Read the current pp_control value, unlocking the register if it
  * is locked
@@ -1147,7 +1164,7 @@ static void ironlake_panel_vdd_off_sync(struct intel_dp *intel_dp)
 		I915_READ(pp_stat_reg), I915_READ(pp_ctrl_reg));
 
 		if ((pp & POWER_TARGET_ON) == 0)
-			msleep(intel_dp->panel_power_cycle_delay);
+			intel_dp->last_power_cycle = jiffies;
 
 		intel_runtime_pm_put(dev_priv);
 	}
@@ -1222,6 +1239,7 @@ void ironlake_edp_panel_on(struct intel_dp *intel_dp)
 	POSTING_READ(pp_ctrl_reg);
 
 	ironlake_wait_panel_on(intel_dp);
+	intel_dp->last_power_on = jiffies;
 
 	if (IS_GEN5(dev)) {
 		pp |= PANEL_POWER_RESET; /* restore panel reset bit */
@@ -1242,6 +1260,8 @@ void ironlake_edp_panel_off(struct intel_dp *intel_dp)
 
 	DRM_DEBUG_KMS("Turn eDP power off\n");
 
+	ironlake_edp_wait_backlight_off(intel_dp);
+
 	pp = ironlake_get_pp_control(intel_dp);
 	/* We need to switch off panel power _and_ force vdd, for otherwise some
 	 * panels get very unhappy and cease to work. */
@@ -1252,6 +1272,7 @@ void ironlake_edp_panel_off(struct intel_dp *intel_dp)
 	I915_WRITE(pp_ctrl_reg, pp);
 	POSTING_READ(pp_ctrl_reg);
 
+	intel_dp->last_power_cycle = jiffies;
 	ironlake_wait_panel_off(intel_dp);
 }
 
@@ -1273,7 +1294,7 @@ void ironlake_edp_backlight_on(struct intel_dp *intel_dp)
 	 * link.  So delay a bit to make sure the image is solid before
 	 * allowing it to appear.
 	 */
-	msleep(intel_dp->backlight_on_delay);
+	ironlake_wait_backlight_on(intel_dp);
 	pp = ironlake_get_pp_control(intel_dp);
 	pp |= EDP_BLC_ENABLE;
 
@@ -1305,7 +1326,7 @@ void ironlake_edp_backlight_off(struct intel_dp *intel_dp)
 
 	I915_WRITE(pp_ctrl_reg, pp);
 	POSTING_READ(pp_ctrl_reg);
-	msleep(intel_dp->backlight_off_delay);
+	intel_dp->last_backlight_off = jiffies;
 }
 
 static void ironlake_edp_pll_on(struct intel_dp *intel_dp)
diff --git a/drivers/gpu/drm/i915/intel_drv.h b/drivers/gpu/drm/i915/intel_drv.h
index 46aea6c..92de688 100644
--- a/drivers/gpu/drm/i915/intel_drv.h
+++ b/drivers/gpu/drm/i915/intel_drv.h
@@ -485,6 +485,9 @@ struct intel_dp {
 	int backlight_off_delay;
 	struct delayed_work panel_vdd_work;
 	bool want_panel_vdd;
+	unsigned long last_power_cycle;
+	unsigned long last_power_on;
+	unsigned long last_backlight_off;
 	bool psr_setup_done;
 	struct intel_connector *attached_connector;
 };
-- 
1.8.3.1