drm/i915: Push i915_sw_fence_wait into the nonblocking atomic commit

Blocking in a worker is ok, that's what the unbound_wq is for. And it
unifies the paths between the blocking and nonblocking commit, giving
me just one path where I have to implement the deadlock avoidance
trickery in the next patch.

I first tried to implement the following patch without this rework, but
force-completing i915_sw_fence creates some serious challenges around
properly cleaning things up. So wasn't a feasible short-term approach.
Another approach would be to simple keep track of all pending atomic
commit work items and manually queue them from the reset code. With the
caveat that double-queue in case we race with the i915_sw_fence must be
avoided. Given all that, taking the cost of a double schedule in atomic
for the short-term fix is the best approach, but can be changed in the future of course.

v2: Amend commit message (Chris).

v3: Add comment explaining why we do nothing in the sw_fence complete
callback (Michel).

Reviewed-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Mika Kuoppala <mika.kuoppala@intel.com>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com> (v2)
Cc: Michel Thierry <michel.thierry@intel.com>
Reviewed-by: Michel Thierry <michel.thierry@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20170808080828.23650-2-daniel.vetter@ffwll.ch

diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
index ee6d3121890ee6368179f141787f0ccb64e01372..519aa240cc4c042e7df81fa154865d7247185bcb 100644 (file)
--- a/drivers/gpu/drm/i915/intel_display.c
+++ b/drivers/gpu/drm/i915/intel_display.c
@@ -12311,6 +12311,8 @@ static void intel_atomic_commit_tail(struct drm_atomic_state *state)
        unsigned crtc_vblank_mask = 0;
        int i;
 
+       i915_sw_fence_wait(&intel_state->commit_ready);
+
        drm_atomic_helper_wait_for_dependencies(state);
 
        if (intel_state->modeset)
@@ -12476,10 +12478,8 @@ intel_atomic_commit_ready(struct i915_sw_fence *fence,
 
        switch (notify) {
        case FENCE_COMPLETE:
-               if (state->base.commit_work.func)
-                       queue_work(system_unbound_wq, &state->base.commit_work);
+               /* we do blocking waits in the worker, nothing to do here */
                break;
-
        case FENCE_FREE:
                {
                        struct intel_atomic_helper *helper =
@@ -12581,14 +12581,14 @@ static int intel_atomic_commit(struct drm_device *dev,
        }
 
        drm_atomic_state_get(state);
-       INIT_WORK(&state->commit_work,
-                 nonblock ? intel_atomic_commit_work : NULL);
+       INIT_WORK(&state->commit_work, intel_atomic_commit_work);
 
        i915_sw_fence_commit(&intel_state->commit_ready);
-       if (!nonblock) {
-               i915_sw_fence_wait(&intel_state->commit_ready);
+       if (nonblock)
+               queue_work(system_unbound_wq, &state->commit_work);
+       else
                intel_atomic_commit_tail(state);
-       }
+
 
        return 0;
 }