Re: [PATCH] drm/i915: Skip fence installation for objects with rotated views (v2)

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

On Tue, Oct 27, 2015 at 06:47:19PM +0000, Chris Wilson wrote:
> On Tue, Oct 27, 2015 at 08:35:36PM +0200, Ville Syrjälä wrote:
> > On Tue, Oct 27, 2015 at 06:03:52PM +0000, Chris Wilson wrote:
> > > On Tue, Oct 27, 2015 at 02:26:55PM +0000, Tvrtko Ursulin wrote:
> > > > 
> > > > On 27/10/15 13:48, Ville Syrjälä wrote:
> > > > >On Tue, Oct 27, 2015 at 01:34:44PM +0000, Tvrtko Ursulin wrote:
> > > > >>
> > > > >>On 27/10/15 12:51, Ville Syrjälä wrote:
> > > > >>>On Mon, Oct 26, 2015 at 06:23:26PM -0700, Vivek Kasireddy wrote:
> > > > >>>>While pinning a fb object to the display plane, only install a fence
> > > > >>>>if the object is using a normal view. This corresponds with the
> > > > >>>>behavior found in i915_gem_object_do_pin() where the fencability
> > > > >>>>criteria is determined only for objects with normal views.
> > > > >>>>
> > > > >>>>v2:
> > > > >>>>Look at the object's map_and_fenceable flag to determine whether to
> > > > >>>>install a fence or not (Chris).
> > > > >>>>
> > > > >>>>Cc: Chris Wilson <chris@chris-wilson.co.uk>
> > > > >>>>Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
> > > > >>>>Cc: Daniel Vetter <daniel@ffwll.ch>
> > > > >>>>Signed-off-by: Vivek Kasireddy <vivek.kasireddy@intel.com>
> > > > >>>>---
> > > > >>>>   drivers/gpu/drm/i915/intel_display.c | 3 ++-
> > > > >>>>   1 file changed, 2 insertions(+), 1 deletion(-)
> > > > >>>>
> > > > >>>>diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
> > > > >>>>index 52fb3f2..108c000 100644
> > > > >>>>--- a/drivers/gpu/drm/i915/intel_display.c
> > > > >>>>+++ b/drivers/gpu/drm/i915/intel_display.c
> > > > >>>>@@ -2357,7 +2357,8 @@ intel_pin_and_fence_fb_obj(struct drm_plane *plane,
> > > > >>>>   	 * framebuffer compression.  For simplicity, we always install
> > > > >>>>   	 * a fence as the cost is not that onerous.
> > > > >>>>   	 */
> > > > >>>>-	ret = i915_gem_object_get_fence(obj);
> > > > >>>>+	if (obj->map_and_fenceable)
> > > > >>>
> > > > >>>This will now get the fence and pin it for the 90/270 view as well,
> > > > >>>even though the fence doesn't even cover that particualr gtt mapping.
> > > > >>
> > > > >>I don't follow. obj->map_and_fenceable will be true only when normal
> > > > >>view exists, so this avoids setting up the fence when no normal view
> > > > >>exists and so avoids the WARN_ON in i915_gem_object_get_fence.
> > > > >
> > > > >Sure, but it's pointless to use up a fence if all we care about
> > > > >is the 90/270 mapping.
> > > > 
> > > > After a brief IRC discussion we agreed that the patch doesn't
> > > > introduce any new negative behaviours.
> > > 
> > > Urm, consider
> > > 
> > > intel_unpin_fb_obj():
> > > 	...
> > > 	i915_gem_object_unpin_fence(intel_fb_obj(obj));
> > 
> > We'll have (pointlessly) pinned the fence too, so I think it'll end up
> > working. I would have just put in view==NORMAL checks myself as an
> > interim solution to avoid that, but whatever.
> 
> No, it didn't. If we rotated first, we don't get a fence and so don't
> pin it. Then we attach an unrotated, grab a fence and pin it. Then we
> end up unpinning twice vs a single pin.

Oh, map_and_fenceable on the _object_ depends whether the normal view is
bound, and yeah it could get bound only after the rotated view got used
for scanout. So view==NORMAL for now seems like good enough solution for
now to me. Anything else means a bigger rework of the code, and I for
one don't want to got there until I've managed to land my already pending
stuff.

-- 
Ville Syrjälä
Intel OTC
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