Re: [RFC PATCH 5/5] drm/atomic: Make async plane update checks work as intended.

[Maarten Lankhorst <maarten.lankhorst@linux.intel.com>]

Op 30-08-17 om 14:46 schreef Daniel Vetter:
> On Wed, Aug 30, 2017 at 02:17:52PM +0200, Maarten Lankhorst wrote:
>> By always keeping track of the last commit in plane_state, we know
>> whether there is an active update on the plane or not. With that
>> information we can reject the fast update, and force the slowpath
>> to be used as was originally intended.
>>
>> Cc: Gustavo Padovan <gustavo.padovan@collabora.com>
>> Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
> Makes sense, but I think like patch 1 it would be better to do this in a
> separate series. Which would then include a patch to move i915 over to the
> async plane support.
>
> One more comment below.
>
>> ---
>>  drivers/gpu/drm/drm_atomic_helper.c  | 25 +++++++++++--------------
>>  drivers/gpu/drm/i915/intel_display.c |  8 ++++++++
>>  include/drm/drm_plane.h              |  5 +++--
>>  3 files changed, 22 insertions(+), 16 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/drm_atomic_helper.c b/drivers/gpu/drm/drm_atomic_helper.c
>> index 034f563fb130..384d99347bb3 100644
>> --- a/drivers/gpu/drm/drm_atomic_helper.c
>> +++ b/drivers/gpu/drm/drm_atomic_helper.c
>> @@ -1388,8 +1388,8 @@ int drm_atomic_helper_async_check(struct drm_device *dev,
>>  {
>>  	struct drm_crtc *crtc;
>>  	struct drm_crtc_state *crtc_state;
>> -	struct drm_plane *__plane, *plane = NULL;
>> -	struct drm_plane_state *__plane_state, *plane_state = NULL;
>> +	struct drm_plane *plane;
>> +	struct drm_plane_state *old_plane_state, *new_plane_state;
>>  	const struct drm_plane_helper_funcs *funcs;
>>  	int i, n_planes = 0;
>>  
>> @@ -1398,33 +1398,33 @@ int drm_atomic_helper_async_check(struct drm_device *dev,
>>  			return -EINVAL;
>>  	}
>>  
>> -	for_each_new_plane_in_state(state, __plane, __plane_state, i) {
>> +	for_each_oldnew_plane_in_state(state, plane, old_plane_state, new_plane_state, i)
>>  		n_planes++;
>> -		plane = __plane;
>> -		plane_state = __plane_state;
>> -	}
>>  
>>  	/* FIXME: we support only single plane updates for now */
>> -	if (!plane || n_planes != 1)
>> +	if (n_planes != 1)
>>  		return -EINVAL;
>>  
>> -	if (!plane_state->crtc)
>> +	if (!new_plane_state->crtc)
>>  		return -EINVAL;
>>  
>>  	funcs = plane->helper_private;
>>  	if (!funcs->atomic_async_update)
>>  		return -EINVAL;
>>  
>> -	if (plane_state->fence)
>> +	if (new_plane_state->fence)
>>  		return -EINVAL;
>>  
>>  	/*
>> -	 * TODO: Don't do an async update if there is an outstanding commit modifying
>> +	 * Don't do an async update if there is an outstanding commit modifying
>>  	 * the plane.  This prevents our async update's changes from getting
>>  	 * overridden by a previous synchronous update's state.
>>  	 */
>> +	if (old_plane_state->commit &&
>> +	    !try_wait_for_completion(&old_plane_state->commit->hw_done))
>> +		return -EBUSY;
> Instead of forcing us to always set the plane_state->commit pointer (bunch
> of pointles refcounting), perhaps just check
> plane_state->crtc->state->commit? We do hold the necessary locks to at
> least look at that.
Then we'd always take the slowpath?

The point here was to check whether the current plane was part of the most recent commit, to know this we must either add a flip_planes mask member to drm_crtc_commit, or add a pointer in plane_state to the most recent commit it was part of.
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