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

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

On Thu, Mar 22, 2018 at 01:05:24AM +0000, Pandiyan, Dhinakaran wrote:
> 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@linux.intel.com>
> > > Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
> > > Cc: Daniel Vetter <daniel.vetter@intel.com>
> > > Signed-off-by: Dhinakaran Pandiyan <dhinakaran.pandiyan@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.

Hmm. ktime_t is 64 bits so I guess on 32bit systems it could be a slight
issue. Not sure we should care that much about PSR debug on 32bit though.
It's a rather unlikely configuration, and at least we don't do that in 
the ci.

> 
> > 
> > > +	}
> > > +
> > >  	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
> > 

-- 
Ville Syrjälä
Intel OTC
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