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

[Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>]

On 27/10/15 18:58, Ville Syrjälä wrote:
> 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.

Right, so one WARN eliminated, one to go. :)

Vivek would you have the time to add a new test case which will hit a 
WARN in i915_gem_object_unpin_fence with the v2 of your patch and post a 
v3 which fixes it?

Regards,

Tvrtko
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