Re: [RFC 8/8] drm/i915: Add two-stage ILK-style watermark programming (v2)

[Daniel Vetter <daniel@ffwll.ch>]

On Mon, Jul 06, 2015 at 02:20:00PM +0200, Maarten Lankhorst wrote:
> Op 02-07-15 om 04:26 schreef Matt Roper:
> > From: Matt Roper <matt@mattrope.com>
> >
> > In addition to calculating final watermarks, let's also pre-calculate a
> > set of intermediate watermark values at atomic check time.  These
> > intermediate watermarks are a combination of the watermarks for the old
> > state and the new state; they should satisfy the requirements of both
> > states which means they can be programmed immediately when we commit the
> > atomic state (without waiting for a vblank).  Once the vblank does
> > happen, we can then re-program watermarks to the more optimal final
> > value.
> >
> > v2: Significant rebasing/rewriting.
> >
> > Signed-off-by: Matt Roper <matthew.d.roper@intel.com>
> > ---
> >  drivers/gpu/drm/i915/i915_drv.h      |  9 +++++
> >  drivers/gpu/drm/i915/i915_irq.c      |  7 ++++
> >  drivers/gpu/drm/i915/intel_display.c | 34 +++++++++++++++-
> >  drivers/gpu/drm/i915/intel_drv.h     | 26 +++++++++----
> >  drivers/gpu/drm/i915/intel_pm.c      | 75 ++++++++++++++++++++++++++++++------
> >  5 files changed, 130 insertions(+), 21 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
> > index 5ad942e..42397e2 100644
> > --- a/drivers/gpu/drm/i915/i915_drv.h
> > +++ b/drivers/gpu/drm/i915/i915_drv.h
> > @@ -623,6 +623,9 @@ struct drm_i915_display_funcs {
> >  			  struct dpll *best_clock);
> >  	int (*compute_pipe_wm)(struct drm_crtc *crtc,
> >  			       struct drm_atomic_state *state);
> > +	void (*compute_intermediate_wm)(struct drm_device *dev,
> > +					struct intel_crtc_state *newstate,
> > +					const struct intel_crtc_state *oldstate);
> >
> If this is can't fail anyway could we please do this at runtime instead of precalculating?

Hm, this is possible to fail, we might not be able to get valid
intermediate wms. And therefore it needs to be in the compute phase.
-Daniel

> 
> Something like this:
> 
> commit_intermediate_wm
> vblank_evade
> plane_update
> vblank_end
> (wait for vblank)
> commit_final_wm
> 
> Of course for skylake just hammer in the final wm during vblank evasion. :-)
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-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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