[Intel-gfx] [PATCH 5/5] drm/i915/psr: Timestamps for PSR entry and exit interrupts.

[Pandiyan, Dhinakaran]

On Wed, 2018-03-21 at 21:48 +0200, Ville Syrjälä wrote:
> On Tue, Mar 20, 2018 at 03:41:51PM -0700, Dhinakaran Pandiyan wrote:
> > Timestamps are useful for IGT tests that trigger PSR exit and/or wait for
> > PSR entry.
> > 
> > Cc: Ville Syrjälä <ville.syrjala at linux.intel.com>
> > Cc: Rodrigo Vivi <rodrigo.vivi at intel.com>
> > Cc: Daniel Vetter <daniel.vetter at intel.com>
> > Signed-off-by: Dhinakaran Pandiyan <dhinakaran.pandiyan at intel.com>
> > ---
> >  drivers/gpu/drm/i915/i915_debugfs.c | 12 ++++++++++++
> >  drivers/gpu/drm/i915/i915_drv.h     |  3 +++
> >  drivers/gpu/drm/i915/intel_psr.c    | 21 +++++++++++++++++++--
> >  3 files changed, 34 insertions(+), 2 deletions(-)
> > 
> > diff --git a/drivers/gpu/drm/i915/i915_debugfs.c b/drivers/gpu/drm/i915/i915_debugfs.c
> > index 669f3d56054a..d28dc4d8388e 100644
> > --- a/drivers/gpu/drm/i915/i915_debugfs.c
> > +++ b/drivers/gpu/drm/i915/i915_debugfs.c
> > @@ -2686,6 +2686,18 @@ static int i915_edp_psr_status(struct seq_file *m, void *data)
> >  	}
> >  	mutex_unlock(&dev_priv->psr.lock);
> >  
> > +	if (READ_ONCE(dev_priv->psr.debug)) {
> > +		unsigned int seq;
> > +
> > +		do {
> > +			seq = read_seqbegin(&dev_priv->psr.debug_lock);
> > +			seq_printf(m, "Last attempted entry at: %lld\n",
> > +				   dev_priv->psr.last_entry_attempt);
> > +			seq_printf(m, "Last exit at: %lld\n",
> > +				   dev_priv->psr.last_exit);
> > +		} while (read_seqretry(&dev_priv->psr.debug_lock, seq));
> 
> What does the seqlock buy us?

Reading debugfs wouldn't block the update inside the irq handler,
compared to using a spinlock. We need to serialize the read and update
parts, don't we? Otherwise tests might end up reading partial updates.

> 
> > +	}
> > +
> >  	intel_runtime_pm_put(dev_priv);
> >  	return 0;
> >  }
> > diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
> > index 136fa2267a66..b8170882e1ab 100644
> > --- a/drivers/gpu/drm/i915/i915_drv.h
> > +++ b/drivers/gpu/drm/i915/i915_drv.h
> > @@ -609,6 +609,9 @@ struct i915_psr {
> >  	bool alpm;
> >  	bool has_hw_tracking;
> >  	bool debug;
> > +	ktime_t last_entry_attempt;
> > +	ktime_t last_exit;
> > +	seqlock_t debug_lock;
> >  
> >  	void (*enable_source)(struct intel_dp *,
> >  			      const struct intel_crtc_state *);
> > diff --git a/drivers/gpu/drm/i915/intel_psr.c b/drivers/gpu/drm/i915/intel_psr.c
> > index 64ecea80438d..a83d95b1b587 100644
> > --- a/drivers/gpu/drm/i915/intel_psr.c
> > +++ b/drivers/gpu/drm/i915/intel_psr.c
> > @@ -125,28 +125,44 @@ void intel_psr_irq_handler(struct drm_i915_private *dev_priv, u32 psr_iir)
> >  {
> >  	u32 transcoders = BIT(TRANSCODER_EDP);
> >  	enum transcoder cpu_transcoder;
> > +	ktime_t time_ns =  ktime_get();
> > +	unsigned long flags = 0;
> >  
> >  	if (INTEL_GEN(dev_priv) >= 8)
> >  		transcoders |= BIT(TRANSCODER_A) |
> >  			       BIT(TRANSCODER_B) |
> >  			       BIT(TRANSCODER_C);
> >  
> > +	write_seqlock_irqsave(&dev_priv->psr.debug_lock, flags);
> >  	for_each_cpu_transcoder_masked(dev_priv, cpu_transcoder, transcoders) {
> > +		bool handled = false;
> > +
> > +		/* PSR supported only on one transcoder currently */
> > +		WARN_ON_ONCE(handled);
> > +
> >  		/* FIXME: Exit PSR when this happens. */
> > -		if (psr_iir & EDP_PSR_ERROR(cpu_transcoder))
> > +		if (psr_iir & EDP_PSR_ERROR(cpu_transcoder)) {
> > +			handled = true;
> >  			DRM_DEBUG_KMS("[transcoder %s] PSR aux error\n",
> >  				      transcoder_name(cpu_transcoder));
> >  
> > +		}
> > +
> >  		if (psr_iir & EDP_PSR_PRE_ENTRY(cpu_transcoder)) {
> > -			DRM_DEBUG_KMS("[transcoder %s] PSR entry in 2 vblanks\n",
> > +			handled = true;
> > +			dev_priv->psr.last_entry_attempt = time_ns;
> > +			DRM_DEBUG_KMS("[transcoder %s] PSR entry attempt in 2 vblanks\n",
> >  				      transcoder_name(cpu_transcoder));
> >  		}
> >  
> >  		if (psr_iir & EDP_PSR_POST_EXIT(cpu_transcoder)) {
> > +			handled = true;
> > +			dev_priv->psr.last_exit = time_ns;
> >  			DRM_DEBUG_KMS("[transcoder %s] PSR exit completed\n",
> >  				      transcoder_name(cpu_transcoder));
> >  		}
> >  	}
> > +	write_sequnlock_irqrestore(&dev_priv->psr.debug_lock, flags);
> >  }
> >  
> >  static bool intel_dp_get_y_cord_status(struct intel_dp *intel_dp)
> > @@ -1160,6 +1176,7 @@ void intel_psr_init(struct drm_i915_private *dev_priv)
> >  
> >  	INIT_DELAYED_WORK(&dev_priv->psr.work, intel_psr_work);
> >  	mutex_init(&dev_priv->psr.lock);
> > +	seqlock_init(&dev_priv->psr.debug_lock);
> >  
> >  	if (IS_VALLEYVIEW(dev_priv) || IS_CHERRYVIEW(dev_priv)) {
> >  		dev_priv->psr.enable_source = vlv_psr_enable_source;
> > -- 
> > 2.14.1
>