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

Chris Wilson
2015-10-27T18:03:59Z

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));

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