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

[Jani Nikula <jani.nikula@linux.intel.com>]

On Thu, 19 Dec 2013, 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);
> +}

I think the naming here is a bit unfortunate. You call wait_backlight_on()
*before* you enable backlight, but wait_backlight_off() *after* you
disable backlight.

The wait_panel_{on,off} functions wait for some event to happen.

I think ironlake_wait_backlight_on() *sounds* like something to call
*after* you've enabled backlight. So instead, I think the function
should be called something like wait_power_on()... but then it gets
confusing with the wait_panel_on(). Ugh.

I don't know. I'll just say

Reviewed-by: Jani Nikula <jani.nikula@intel.com>

because I think the patch looks good otherwise, and maybe someone will
come up with the Perfect Naming Scheme and send follow-up patches we can
bikeshed until the end of time...

>  
>  /* 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
>
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-- 
Jani Nikula, Intel Open Source Technology Center