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

Jesse Barnes
2013-12-19T17:33:03Z

On Thu, 19 Dec 2013 14:29:40 -0200
Paulo Zanoni <przanoni@gmail.com> wrote:

> 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.
>
> Signed-off-by: Paulo Zanoni <paulo.r.zanoni@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;
> };

We could bikeshed the name all day, but this looks like a great
improvement.

Reviewed-by: Jesse Barnes <jbarnes@virtuousgeek.org>