Re: [PATCH 5/5] drm/i915: Optimize VLV/CHV display FIFO updates

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

On Thu, Mar 09, 2017 at 09:26:36PM +0000, Chris Wilson wrote:
> On Thu, Mar 09, 2017 at 05:44:34PM +0200, ville.syrjala@linux.intel.com wrote:
> > From: Ville Syrjälä <ville.syrjala@linux.intel.com>
> > 
> > Use I915_{READ,WRITE}_FW() for updating the DSPARB registers on
> > VLV/CHV. This is less expesive as we can grab the uncore.lock across
> > the entire sequence of reads and writes instead of each register
> > access grabbing it.
> > 
> > This also allows us to eliminate the dsparb lock entirely as the
> > uncore.lock now effectively protects the contents of the DSPARB
> > registers.
> > 
> > Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
> > ---
> >  drivers/gpu/drm/i915/i915_drv.c |  1 -
> >  drivers/gpu/drm/i915/i915_drv.h |  3 ---
> >  drivers/gpu/drm/i915/intel_pm.c | 36 +++++++++++++++++++++---------------
> >  3 files changed, 21 insertions(+), 19 deletions(-)
> > 
> > diff --git a/drivers/gpu/drm/i915/i915_drv.c b/drivers/gpu/drm/i915/i915_drv.c
> > index b1e9027a4f80..debb74a2b2a9 100644
> > --- a/drivers/gpu/drm/i915/i915_drv.c
> > +++ b/drivers/gpu/drm/i915/i915_drv.c
> > @@ -827,7 +827,6 @@ static int i915_driver_init_early(struct drm_i915_private *dev_priv,
> >  
> >  	spin_lock_init(&dev_priv->mm.object_stat_lock);
> >  	spin_lock_init(&dev_priv->mmio_flip_lock);
> > -	spin_lock_init(&dev_priv->wm.dsparb_lock);
> >  	mutex_init(&dev_priv->sb_lock);
> >  	mutex_init(&dev_priv->modeset_restore_lock);
> >  	mutex_init(&dev_priv->av_mutex);
> > diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
> > index 3002996ddbed..6af0b1d33cab 100644
> > --- a/drivers/gpu/drm/i915/i915_drv.h
> > +++ b/drivers/gpu/drm/i915/i915_drv.h
> > @@ -2375,9 +2375,6 @@ struct drm_i915_private {
> >  	} sagv_status;
> >  
> >  	struct {
> > -		/* protects DSPARB registers on pre-g4x/vlv/chv */
> > -		spinlock_t dsparb_lock;
> > -
> >  		/*
> >  		 * Raw watermark latency values:
> >  		 * in 0.1us units for WM0,
> > diff --git a/drivers/gpu/drm/i915/intel_pm.c b/drivers/gpu/drm/i915/intel_pm.c
> > index 99e09f63d4b3..24cdc13a416a 100644
> > --- a/drivers/gpu/drm/i915/intel_pm.c
> > +++ b/drivers/gpu/drm/i915/intel_pm.c
> > @@ -1358,13 +1358,19 @@ static void vlv_atomic_update_fifo(struct intel_atomic_state *state,
> >  
> >  	trace_vlv_fifo_size(crtc, sprite0_start, sprite1_start, fifo_size);
> >  
> > -	spin_lock(&dev_priv->wm.dsparb_lock);
> > +	/*
> > +	 * uncore.lock serves a double purpose here. It allows us to
> > +	 * use the less expensive I915_{READ,WRITE}_FW() functions, and
> > +	 * it protects the DSPARB registers from getting clobbered by
> > +	 * parallel updates from multiple pipes.
> > +	 */
> > +	spin_lock(&dev_priv->uncore.lock);
> 
> Might be nice to document that the irq is disabled by
> intel_pipe_update_start() (hence why spin_lock is safe).

Sure. I'll add a note.

-- 
Ville Syrjälä
Intel OTC
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