Re: [PATCH] drm/i915: make sure GPU freq drops to minimum after entering RC6 v3

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

On Tue, 23 Apr 2013, Jesse Barnes <jbarnes@virtuousgeek.org> wrote:
> On VLV, the Punit doesn't automatically drop the GPU to it's minimum
> voltage level when entering RC6, so we arm a timer to do it for us from
> the RPS interrupt handler.  It'll generally only fire when we go idle
> (or if for some reason there's a long delay between RPS interrupts), but
> won't be re-armed again until the next RPS event, so shouldn't affect
> power consumption after we go idle and it triggers.
>
> v2: use delayed work instead of timer + work queue combo (Ville)
> v3: fix up delayed work cancel (must be outside lock) (Daniel)
>     fix up delayed work handling func for delayed work (Jesse)
>
> Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>
> ---
>  drivers/gpu/drm/i915/i915_drv.h |    2 ++
>  drivers/gpu/drm/i915/i915_irq.c |   11 +++++++++++
>  drivers/gpu/drm/i915/intel_pm.c |   22 ++++++++++++++++++++++
>  3 files changed, 35 insertions(+)
>
> diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
> index 2557fc7..f563f25 100644
> --- a/drivers/gpu/drm/i915/i915_drv.h
> +++ b/drivers/gpu/drm/i915/i915_drv.h
> @@ -660,6 +660,7 @@ struct i915_suspend_saved_registers {
>  
>  struct intel_gen6_power_mgmt {
>  	struct work_struct work;
> +	struct delayed_work vlv_work;
>  	u32 pm_iir;
>  	/* lock - irqsave spinlock that protectects the work_struct and
>  	 * pm_iir. */
> @@ -670,6 +671,7 @@ struct intel_gen6_power_mgmt {
>  	u8 cur_delay;
>  	u8 min_delay;
>  	u8 max_delay;
> +	u8 rpe_delay;
>  	u8 hw_max;
>  
>  	struct delayed_work delayed_resume_work;
> diff --git a/drivers/gpu/drm/i915/i915_irq.c b/drivers/gpu/drm/i915/i915_irq.c
> index 932e7f8..af385e2 100644
> --- a/drivers/gpu/drm/i915/i915_irq.c
> +++ b/drivers/gpu/drm/i915/i915_irq.c
> @@ -488,6 +488,17 @@ static void gen6_pm_rps_work(struct work_struct *work)
>  			gen6_set_rps(dev_priv->dev, new_delay);
>  	}
>  
> +	if (IS_VALLEYVIEW(dev_priv->dev)) {
> +		/*
> +		 * On VLV, when we enter RC6 we may not be at the minimum
> +		 * voltage level, so arm a timer to check.  It should only
> +		 * fire when there's activity or once after we've entered
> +		 * RC6, and then won't be re-armed until the next RPS interrupt.
> +		 */
> +		mod_delayed_work(dev_priv->wq, &dev_priv->rps.vlv_work,
> +				 jiffies + msecs_to_jiffies(100));

Hooray for conflicting semantics. Unlike mod_timer, mod_delayed_work
wants a delay, not an absolute time in jiffies.

> +	}
> +
>  	mutex_unlock(&dev_priv->rps.hw_lock);
>  }
>  
> diff --git a/drivers/gpu/drm/i915/intel_pm.c b/drivers/gpu/drm/i915/intel_pm.c
> index 2557926..c106187 100644
> --- a/drivers/gpu/drm/i915/intel_pm.c
> +++ b/drivers/gpu/drm/i915/intel_pm.c
> @@ -2822,6 +2822,23 @@ int valleyview_rps_min_freq(struct drm_i915_private *dev_priv)
>  	return val & 0xff;
>  }
>  
> +static void vlv_rps_timer_work(struct work_struct *work)
> +{
> +	drm_i915_private_t *dev_priv = container_of(work, drm_i915_private_t,
> +						    rps.vlv_work.work);
> +
> +	/*
> +	 * Timer fired, we must be idle.  Drop to min voltage state.
> +	 * Note: we use RPe here since it should match the
> +	 * Vmin we were shooting for.  That should give us better
> +	 * perf when we come back out of RC6 than if we used the
> +	 * min freq available.
> +	 */
> +	mutex_lock(&dev_priv->rps.hw_lock);
> +	valleyview_set_rps(dev_priv->dev, dev_priv->rps.rpe_delay);
> +	mutex_unlock(&dev_priv->rps.hw_lock);
> +}
> +
>  static void valleyview_enable_rps(struct drm_device *dev)
>  {
>  	struct drm_i915_private *dev_priv = dev->dev_private;
> @@ -2886,6 +2903,7 @@ static void valleyview_enable_rps(struct drm_device *dev)
>  	rpe = valleyview_rps_rpe_freq(dev_priv);
>  	DRM_DEBUG_DRIVER("RPe GPU freq: %d\n",
>  			 vlv_gpu_freq(dev_priv->mem_freq, rpe));
> +	dev_priv->rps.rpe_delay = rpe;
>  
>  	val = valleyview_rps_min_freq(dev_priv);
>  	DRM_DEBUG_DRIVER("min GPU freq: %d\n", vlv_gpu_freq(dev_priv->mem_freq,
> @@ -2895,6 +2913,8 @@ static void valleyview_enable_rps(struct drm_device *dev)
>  	DRM_DEBUG_DRIVER("setting GPU freq to %d\n",
>  			 vlv_gpu_freq(dev_priv->mem_freq, rpe));
>  
> +	INIT_DELAYED_WORK(&dev_priv->rps.vlv_work, vlv_rps_timer_work);
> +
>  	valleyview_set_rps(dev_priv->dev, rpe);
>  
>  	/* requires MSI enabled */
> @@ -3640,6 +3660,8 @@ void intel_disable_gt_powersave(struct drm_device *dev)
>  		mutex_lock(&dev_priv->rps.hw_lock);
>  		gen6_disable_rps(dev);
>  		mutex_unlock(&dev_priv->rps.hw_lock);

Theoretically the work could get executed here, between unlock and
cancel. Does that matter?

> +		if (IS_VALLEYVIEW(dev))
> +			cancel_delayed_work_sync(&dev_priv->rps.vlv_work);
>  	}
>  }
>  
> -- 
> 1.7.10.4
>
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