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

Paulo Zanoni
2014-01-03T19:45:31Z

From: Paulo Zanoni <paulo.r.zanoni@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.
v5: - Fix schedule_timeout_interruptible usage: it uses jiffies.

Signed-off-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
---
drivers/gpu/drm/i915/i915_drv.h | 27 +++++++++++++++++++++++++++
drivers/gpu/drm/i915/intel_dp.c | 27 ++++++++++++++++++++++++---
drivers/gpu/drm/i915/intel_drv.h | 3 +++
3 files changed, 54 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
index cc8afff..0131ab0 100644
--- a/drivers/gpu/drm/i915/i915_drv.h
+++ b/drivers/gpu/drm/i915/i915_drv.h
@@ -2636,4 +2636,31 @@ 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, remaining_jiffies;
+
+ /*
+ * 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_jiffies = (long)target_jiffies - (long)tmp_jiffies;
+ while (remaining_jiffies)
+ remaining_jiffies =
+ schedule_timeout_uninterruptible(remaining_jiffies);
+ }
+}
+
#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;
};
--
1.8.4.2