Re: [PATCH 7/7] drm/i915: vlv: handle only enabled pipestat interrupt events

["Ville Syrjälä" <ville.syrjala@linux.intel.com>]

On Tue, Feb 04, 2014 at 09:35:51PM +0200, Imre Deak wrote:
> Atm we call the handlers for pending pipestat interrupt events even if
> they aren't explicitly enabled by i915_enable_pipestat(). This isn't an
> issue for events other than the vblank start event, since those are
> always enabled anyways. Otoh, we enable the vblank start event
> on-demand, so we'll end up calling the vblank handler at times when they
> are disabled.
> 
> I haven't checked if this causes any real problem, but for consistency
> and to remove some overhead we should still fix this by clearing /
> handling only the enabled interrupt events. Also this is a dependency
> for the upcoming VLV power domain patchset where we need to disable all
> the pipestat interrupts whenever the display power well is off.
> 
> Signed-off-by: Imre Deak <imre.deak@intel.com>
> ---
>  drivers/gpu/drm/i915/i915_drv.h |  1 +
>  drivers/gpu/drm/i915/i915_irq.c | 33 ++++++++++++++++++++++++++++++---
>  drivers/gpu/drm/i915/i915_reg.h |  4 ++++
>  3 files changed, 35 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
> index 43f37ca..faca5b4 100644
> --- a/drivers/gpu/drm/i915/i915_drv.h
> +++ b/drivers/gpu/drm/i915/i915_drv.h
> @@ -1427,6 +1427,7 @@ typedef struct drm_i915_private {
>  	};
>  	u32 gt_irq_mask;
>  	u32 pm_irq_mask;
> +	u32 pipestat_irq_mask[I915_MAX_PIPES];
>  
>  	struct work_struct hotplug_work;
>  	bool enable_hotplug_processing;
> diff --git a/drivers/gpu/drm/i915/i915_irq.c b/drivers/gpu/drm/i915/i915_irq.c
> index eea5398..2cac477 100644
> --- a/drivers/gpu/drm/i915/i915_irq.c
> +++ b/drivers/gpu/drm/i915/i915_irq.c
> @@ -419,6 +419,16 @@ done:
>  	return ret;
>  }
>  
> +static bool __cpu_fifo_underrun_reporting_enabled(struct drm_device *dev,
> +						  enum pipe pipe)
> +{
> +	struct drm_i915_private *dev_priv = dev->dev_private;
> +	struct drm_crtc *crtc = dev_priv->pipe_to_crtc_mapping[pipe];
> +	struct intel_crtc *intel_crtc = to_intel_crtc(crtc);
> +
> +	return !intel_crtc->cpu_fifo_underrun_disabled;
> +}
> +
>  /**
>   * intel_set_pch_fifo_underrun_reporting - enable/disable FIFO underrun messages
>   * @dev: drm device
> @@ -520,6 +530,8 @@ i915_enable_pipestat(drm_i915_private_t *dev_priv, enum pipe pipe,
>  	if ((pipestat & enable_mask) == enable_mask)
>  		return;
>  
> +	dev_priv->pipestat_irq_mask[pipe] |= status_mask;
> +
>  	/* Enable the interrupt, clear any pending status */
>  	pipestat |= enable_mask | status_mask;
>  	I915_WRITE(reg, pipestat);
> @@ -550,6 +562,8 @@ i915_disable_pipestat(drm_i915_private_t *dev_priv, enum pipe pipe,
>  	if ((pipestat & enable_mask) == 0)
>  		return;
>  
> +	dev_priv->pipestat_irq_mask[pipe] &= ~status_mask;
> +
>  	pipestat &= ~enable_mask;
>  	I915_WRITE(reg, pipestat);
>  	POSTING_READ(reg);
> @@ -1530,18 +1544,31 @@ static void gen6_rps_irq_handler(struct drm_i915_private *dev_priv, u32 pm_iir)
>  static void valleyview_pipestat_irq_handler(struct drm_device *dev, u32 iir)
>  {
>  	drm_i915_private_t *dev_priv = dev->dev_private;
> -	u32 pipe_stats[I915_MAX_PIPES];
> +	u32 pipe_stats[I915_MAX_PIPES] = { };
>  	int pipe;
>  
>  	spin_lock(&dev_priv->irq_lock);
>  	for_each_pipe(pipe) {
> -		int reg = PIPESTAT(pipe);
> +		int reg;
> +		u32 mask;
> +
> +		if (!dev_priv->pipestat_irq_mask[pipe] &&
> +		    !__cpu_fifo_underrun_reporting_enabled(dev, pipe))
> +			continue;
> +
> +		reg = PIPESTAT(pipe);
>  		pipe_stats[pipe] = I915_READ(reg);
>  
>  		/*
>  		 * Clear the PIPE*STAT regs before the IIR
>  		 */
> -		if (pipe_stats[pipe] & 0x8000ffff)
> +		mask = PIPESTAT_INT_ENABLE_MASK | PIPE_FIFO_UNDERRUN_STATUS;

Maybe we should add PIPE_FIFO_UNDERRUN_STATUS to the mask only when the
underrun reporting is enabled. If someone goes and enables underrun
reporting just after valleyview_pipestat_irq_handler(), we'd
potentially report a stale underrun.

You get to blame me for that one though, since the bug is already there
in the current code, which I implemented.

> +		if (iir & I915_DISPLAY_PIPE_EVENT_INTERRUPT(pipe))
> +			mask |= dev_priv->pipestat_irq_mask[pipe];
> +		pipe_stats[pipe] &= mask;
> +
> +		if (pipe_stats[pipe] & (PIPE_FIFO_UNDERRUN_STATUS |
> +					PIPESTAT_INT_STATUS_MASK))
>  			I915_WRITE(reg, pipe_stats[pipe]);
>  	}
>  	spin_unlock(&dev_priv->irq_lock);
> diff --git a/drivers/gpu/drm/i915/i915_reg.h b/drivers/gpu/drm/i915/i915_reg.h
> index c998c4f..47e0635 100644
> --- a/drivers/gpu/drm/i915/i915_reg.h
> +++ b/drivers/gpu/drm/i915/i915_reg.h
> @@ -997,6 +997,10 @@
>  #define I915_DISPLAY_PIPE_A_EVENT_INTERRUPT		(1<<6)
>  #define I915_DISPLAY_PIPE_B_VBLANK_INTERRUPT		(1<<5)
>  #define I915_DISPLAY_PIPE_B_EVENT_INTERRUPT		(1<<4)
> +#define I915_DISPLAY_PIPE_EVENT_INTERRUPT(pipe)				\
> +	((pipe) == PIPE_A ? I915_DISPLAY_PIPE_A_EVENT_INTERRUPT :	\
> +	 I915_DISPLAY_PIPE_B_EVENT_INTERRUPT)
> +
>  #define I915_DEBUG_INTERRUPT				(1<<2)
>  #define I915_USER_INTERRUPT				(1<<1)
>  #define I915_ASLE_INTERRUPT				(1<<0)
> -- 
> 1.8.4
> 
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-- 
Ville Syrjälä
Intel OTC