[PATCH] drm/amdgpu/vcn: Fix video_profile switch race condition

[Sathishkumar S]

There is a race condition which leads to dpm video power
profile switch (disable and enable) during active video
decode on multi-instance VCN hardware.

This patch aims to fix/skip step 3 in the below sequence:

 - inst_1       power_on
 - inst_0(idle) power_off
 - inst_0(idle) video_power_profile OFF (step 3)
 - inst_1       video_power_profile ON during next begin_use

Add flags to track ON/OFF vcn instances and check if all
instances are off before disabling video power profile.

v2: (David Wu)
 - pg_lock is per instance it doesn't help solve the issue.
 - protect flags also with global workload_profile_mutex.

Signed-off-by: Sathishkumar S <sathishkumar.sundararaju at amd.com>
---
 drivers/gpu/drm/amd/amdgpu/amdgpu_vcn.c | 24 +++++++++++++++---------
 drivers/gpu/drm/amd/amdgpu/amdgpu_vcn.h |  4 ++++
 2 files changed, 19 insertions(+), 9 deletions(-)

diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_vcn.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_vcn.c
index 9a76e11d1c18..b677b287dd49 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_vcn.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_vcn.c
@@ -447,7 +447,14 @@ static void amdgpu_vcn_idle_work_handler(struct work_struct *work)
 		vcn_inst->set_pg_state(vcn_inst, AMD_PG_STATE_GATE);
 		mutex_unlock(&vcn_inst->vcn_pg_lock);
 		mutex_lock(&adev->vcn.workload_profile_mutex);
-		if (adev->vcn.workload_profile_active) {
+		if (!adev->vcn.workload_profile_active &&
+		    !(adev->vcn.flags & AMDGPU_VCN_FLAG_VINST_MASK(adev->vcn.num_vcn_inst))) {
+			/* video profile is active , we are holding global workload_profile_mutex.
+			 * it is safe to check if flags are 0 here and be assured that all instances
+			 * are off, since no other begin_use paths can be holding this lock now.
+			 * so off video_power_profile and update workload_profile_active = false
+			 * since all vcn instances are inactive here.
+			 */
 			r = amdgpu_dpm_switch_power_profile(adev, PP_SMC_POWER_PROFILE_VIDEO,
 							    false);
 			if (r)
@@ -470,24 +477,23 @@ void amdgpu_vcn_ring_begin_use(struct amdgpu_ring *ring)
 
 	cancel_delayed_work_sync(&vcn_inst->idle_work);
 
-	/* We can safely return early here because we've cancelled the
-	 * the delayed work so there is no one else to set it to false
-	 * and we don't care if someone else sets it to true.
-	 */
-	if (adev->vcn.workload_profile_active)
-		goto pg_lock;
-
 	mutex_lock(&adev->vcn.workload_profile_mutex);
 	if (!adev->vcn.workload_profile_active) {
+	/* If inactive proceed to ON video_power_profile and update workload_profile_active */
 		r = amdgpu_dpm_switch_power_profile(adev, PP_SMC_POWER_PROFILE_VIDEO,
 						    true);
 		if (r)
 			dev_warn(adev->dev, "(%d) failed to switch to video power profile mode\n", r);
 		adev->vcn.workload_profile_active = true;
 	}
+	/* Holding global workload_profile_mutex, so none of the idle handlers can access flags.
+	 * and cannot OFF video_power_profile at this point. Can safely update vcn.flags to
+	 * indicate active vcn instances, which is visible to any idle handlers who later grab
+	 * this lock and check flags for any active vcn instances.
+	 */
+	adev->vcn.flags |= AMDGPU_VCN_FLAG_VINST_ON(vcn_inst->inst);
 	mutex_unlock(&adev->vcn.workload_profile_mutex);
 
-pg_lock:
 	mutex_lock(&vcn_inst->vcn_pg_lock);
 	vcn_inst->set_pg_state(vcn_inst, AMD_PG_STATE_UNGATE);
 
diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_vcn.h b/drivers/gpu/drm/amd/amdgpu/amdgpu_vcn.h
index b3fb1d0e43fc..a876a182ff88 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_vcn.h
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_vcn.h
@@ -366,6 +366,10 @@ struct amdgpu_vcn {
 	struct mutex            workload_profile_mutex;
 	u32 reg_count;
 	const struct amdgpu_hwip_reg_entry *reg_list;
+#define AMDGPU_VCN_FLAG_VINST_MASK(n)  (BIT(n+1) - 1)
+#define AMDGPU_VCN_FLAG_VINST_ON(n)    (BIT(n))
+#define AMDGPU_VCN_FLAG_VINST_OFF(n)   (~BIT(n))
+	u32 flags;
 };
 
 struct amdgpu_fw_shared_rb_ptrs_struct {
-- 
2.48.1