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 06:03:52PM +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.

> 
> 
> So if the fb is bound both in rotated and non-rotated modes, we will
> have a fence for the object and try to unpin it twice => WARN (Daniel is
> being too nice, once upon a time that was rightfully a BUG for a major
> screwup).
> 
> We want to track the fence state on the vma and associated that vma with
> the plane_state so that the tracking doesn't get so easily confused.
> -Chris
> 
> -- 
> Chris Wilson, Intel Open Source Technology Centre

-- 
Ville Syrjälä
Intel OTC
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