gpu: nvgpu: remove redundant busy()/idle() calls

gk20a_busy() call in channel_syncpt_incr() and corresponding
gk20a_idle() call in channel_update() are redundant since they
are already encapsulated inside another pair of busy/idle calls

This busy/idle pair will be called only from submit_gpfifo()
and submit_gpfifo() already has its own busy/idle which it
preserves for whole path and hence this redundant pair can be
removed

Also, this prevents a dead lock scenario while do_idle() is in
progress as follows :
- in submit_gpfifo() we call first gk20a_busy() which acquires
  busy read semaphore
- in do_idle() we acquire busy write semaphore and wait for
  current jobs to finish
- now submit_gpfifo() encounters second gk20a_busy() and requests
  busy read semaphore again
- this results in dead lock where do_idle() is waiting for
  submit_gpfifo() to complete and submit_gpfifo() is waiting for
  busy lock held by do_idle() and hence it cannot complete

bug 1529160

Change-Id: I96e4368352f693e93524f0f61689b4447e5331ea
Signed-off-by: Deepak Nibade <dnibade@nvidia.com>
Reviewed-on: http://git-master/r/434191
(cherry picked from commit c4315c6caa42bab72ba6017c7ded25f4e9363dec)
Reviewed-on: http://git-master/r/435132
Reviewed-by: Sachin Nikam <snikam@nvidia.com>
Tested-by: Sachin Nikam <snikam@nvidia.com>

1 files changed, 3 insertions, 10 deletions

diff --git a/drivers/gpu/nvgpu/gk20a/channel_sync_gk20a.c b/drivers/gpu/nvgpu/gk20a/channel_sync_gk20a.c
index 677c4b49..a6ca8214 100644
--- a/drivers/gpu/nvgpu/gk20a/channel_sync_gk20a.c
+++ b/drivers/gpu/nvgpu/gk20a/channel_sync_gk20a.c
@@ -233,16 +233,9 @@ static int __gk20a_channel_syncpt_incr(struct gk20a_channel_sync *s,
         thresh = nvhost_syncpt_incr_max_ext(sp->host1x_pdev, sp->id, 1);
 
         if (register_irq) {
-                /* nvhost action_gpfifo_submit_complete releases this ref. */
-                err = gk20a_busy(c->g->dev);
-
-                if (!err) {
-                        err = nvhost_intr_register_notifier(sp->host1x_pdev,
-                                        sp->id, thresh,
-                                        gk20a_channel_syncpt_update, c);
-                        if (err)
-                                gk20a_idle(c->g->dev);
-                }
+                err = nvhost_intr_register_notifier(sp->host1x_pdev,
+                                sp->id, thresh,
+                                gk20a_channel_syncpt_update, c);
 
                 /* Adding interrupt action should never fail. A proper error
                  * handling here would require us to decrement the syncpt max