Re: [PATCH 08/24] drm/i915: Do not add planes from intel_atomic_setup_scalers.

[Matt Roper <matthew.d.roper@intel.com>]

On Wed, Jun 03, 2015 at 12:32:43PM -0700, Konduru, Chandra wrote:
> 
> 
> > -----Original Message-----
> > From: Maarten Lankhorst [mailto:maarten.lankhorst@linux.intel.com]
> > Sent: Wednesday, June 03, 2015 12:02 AM
> > To: Konduru, Chandra; Roper, Matthew D
> > Cc: intel-gfx@lists.freedesktop.org
> > Subject: Re: [Intel-gfx] [PATCH 08/24] drm/i915: Do not add planes from
> > intel_atomic_setup_scalers.
> > 
> > Op 03-06-15 om 03:52 schreef Konduru, Chandra:
> > >
> > >> -----Original Message-----
> > >> From: Roper, Matthew D
> > >> Sent: Tuesday, June 02, 2015 6:30 PM
> > >> To: Maarten Lankhorst
> > >> Cc: intel-gfx@lists.freedesktop.org; Konduru, Chandra
> > >> Subject: Re: [Intel-gfx] [PATCH 08/24] drm/i915: Do not add planes from
> > >> intel_atomic_setup_scalers.
> > >>
> > >> On Mon, Jun 01, 2015 at 03:27:11PM +0200, Maarten Lankhorst wrote:
> > >>> This may postpone going to HQ mode until the plane is in the
> > >>> drm_atomic_state if it's not using scaler 0, but it does allow moving
> > >>> intel_atomic_setup_scalers to the crtc check function.
> > >>>
> > >>> Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
> > >>> ---
> > >>>  drivers/gpu/drm/i915/intel_atomic.c  | 41 ++++++++++++++++++-------------
> > ---
> > >> --
> > >>>  drivers/gpu/drm/i915/intel_display.c | 27 +++++++++++++++---------
> > >>>  drivers/gpu/drm/i915/intel_drv.h     |  2 ++
> > >>>  3 files changed, 39 insertions(+), 31 deletions(-)
> > >>>
> > >>> diff --git a/drivers/gpu/drm/i915/intel_atomic.c
> > >> b/drivers/gpu/drm/i915/intel_atomic.c
> > >>> index 1edd1651c045..a8202fa0daa8 100644
> > >>> --- a/drivers/gpu/drm/i915/intel_atomic.c
> > >>> +++ b/drivers/gpu/drm/i915/intel_atomic.c
> > >>> @@ -100,14 +100,6 @@ int intel_atomic_check(struct drm_device *dev,
> > >>>  	if (ret)
> > >>>  		return ret;
> > >>>
> > >>> -	/*
> > >>> -	 * FIXME: move to crtc atomic check function once this is
> > >>> -	 * more atomic friendly.
> > >>> -	 */
> > >>> -	ret = intel_atomic_setup_scalers(dev, nuclear_crtc, crtc_state);
> > >>> -	if (ret)
> > >>> -		return ret;
> > >>> -
> > >>>  	return ret;
> > >>>  }
> > >>>
> > >>> @@ -336,21 +328,10 @@ int intel_atomic_setup_scalers(struct drm_device
> > >> *dev,
> > >>>  			/* find the plane that set the bit as scaler_user */
> > >>>  			plane = drm_state->planes[i];
> > >>>
> > >>> -			/*
> > >>> -			 * to enable/disable hq mode, add planes that are using
> > >> scaler
> > >>> -			 * into this transaction
> > >>> -			 */
> > >>>  			if (!plane) {
> > >>> -				struct drm_plane_state *state;
> > >>> -				plane = drm_plane_from_index(dev, i);
> > >>> -				state =
> > >> drm_atomic_get_plane_state(drm_state, plane);
> > >>> -				if (IS_ERR(state)) {
> > >>> -					DRM_DEBUG_KMS("Failed to add
> > >> [PLANE:%d] to drm_state\n",
> > >>> -						plane->base.id);
> > >>> -					return PTR_ERR(state);
> > >>> -				}
> > >>> +				DRM_DEBUG_KMS("Failed to find [PLANE:%d]
> > >> in drm_state\n", plane->base.id);
> > >>> +				continue;
> > >>>  			}
> > >>> -
> > >>>  			intel_plane = to_intel_plane(plane);
> > >>>
> > >>>  			/* plane on different crtc cannot be a scaler user of this
> > >> crtc */
> > >>> @@ -396,6 +377,24 @@ int intel_atomic_setup_scalers(struct drm_device
> > >> *dev,
> > >>>  		}
> > >>>  	}
> > >>>
> > >>> +	/* plane not part of mask must leave hq mode? */
> > >>> +	if (num_scalers_need > 1 && scaler_state->scalers[0].in_use &&
> > >>> +	    scaler_state->scalers[0].mode == PS_SCALER_MODE_HQ) {
> > >>> +		scaler_state->scalers[0].mode = PS_SCALER_MODE_DYN;
> > >>> +
> > >>> +		intel_crtc->atomic.skl_update_scaler0 =
> > >>> +			PS_SCALER_EN | PS_SCALER_MODE_DYN;
> > >>> +	}
> > >>> +
> > >>> +	/* plane not part of mask can enter hq mode? */
> > >>> +	if (num_scalers_need == 1 && scaler_state->scalers[0].in_use &&
> > >>> +	    intel_crtc->pipe != PIPE_C && scaler_state->scalers[0].mode !=
> > >> PS_SCALER_MODE_HQ) {
> > >>> +		scaler_state->scalers[0].mode = PS_SCALER_MODE_HQ;
> > >>> +
> > >>> +		intel_crtc->atomic.skl_update_scaler0 =
> > >>> +			PS_SCALER_EN | PS_SCALER_MODE_HQ;
> > >>> +	}
> > >>> +
> > >> I don't have access to the hw spec at the moment; is scaler #0 the only
> > >> one that can ever go into HQ mode?
> > > Yes
> > >
> > >> If there isn't a hardware
> > >> requirement about this, then it seems like we're missing the case where
> > >> planes A and B get scalers 0 and 1.  Then plane A (and thus scaler 0) is
> > >> disabled, which should allow scaler 1 to go into HQ mode.
> > > In this case, scaler 0 to be allocated to plane B to operate in HQ mode.
> > Is it really bad to keep it on scaler 1 for a while until the next time the plane is
> > added?
> > 
> > >> I guess it's not immediately clear to me why we need to not pull the
> > >> other planes into the transaction.  Is this just to avoid doing some
> > >> extra work for a plane that hasn't changed, or does it cause a problem
> > >> somehow?
> > > Per atomic design, unchanged planes can be added to transaction.
> > > And scaler implementation is using this design feature.
> > > Not sure what the issue here, but we need this feature continue
> > > to available.
> > >
> > Unchanged planes can be added, but this could pull in a primary plane, which
> > would need
> > to set atomic.wait_for_flips then. I can do that as special case when adding a
> > plane if
> > that's preferred.
> 
> Here primary plane can get added if that is the only plane using scaler which
> isn't part of the transaction. But here addition of primary plane isn't adding
> or changing its FB. So why it needs to set atomic.wait_for_flips?

In the atomic case, intel_check_primary_plane() sets
atomic.wait_for_flips if the primary plane is part of the original
transaction (no matter what about the primary plane is changing).
However if we pull in the primary plane via
intel_atomic_setup_scalers(), that gets called after we've finished
checking all of the planes (that were originally part of the
transaction), so I don't think wait_for_flips will get set in that case.
So I think pulling in the plane as Chandra was will still avoid an
unnecessary wait.  Even though it's in the transaction, I believe the
'check' step is bypassed (which means we need to be careful about doing
stuff like this if it could affect derived state...but I think in this
case it's safe).

N.B.  The wait we're talking about here will only be triggered when a
SKL or BXT platform disables a "sprite" plane (thus triggering the
primary's scaler to switch to HQ mode) while there's a pending legacy
pageflip on the primary plane.  I don't think we have a userspace today
that can trigger this...Weston won't use sprites at all in a non-atomic
manner and although SNA has an Xv sprite adapter, it won't ever be
performing scaling of the primary plane afaik.


Matt

> 
> > 
> > ~Maarten

-- 
Matt Roper
Graphics Software Engineer
IoTG Platform Enabling & Development
Intel Corporation
(916) 356-2795
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