[PATCH v2] drm/amd/amdgpu: Add Annotations to Process Isolation functions

[Srinivasan Shanmugam]

This update adds explanations to key functions that manage how the
Kernel Fusion Driver (KFD) and Kernel Graphics Driver (KGD) share the
GPU.

amdgpu_gfx_enforce_isolation_wait_for_kfd: Controls the waiting period
for KFD to ensure it takes turns with KGD in using the GPU. It uses a
mutex to safely manage shared data, like timing and state, and tracks
when KFD starts and stops waiting.

amdgpu_gfx_enforce_isolation_ring_begin_use: Ensures KFD has enough time
to run before new tasks are submitted to the GPU ring. It uses a mutex
to synchronize access and may adjust the KFD scheduler.

amdgpu_gfx_enforce_isolation_ring_end_use: Handles cleanup and state
updates when finishing the use of a GPU ring. It may also adjust the KFD
scheduler, using a mutex to manage shared data access.

Cc: Christian König <christian.koenig at amd.com>
Cc: Alex Deucher <alexander.deucher at amd.com>
Signed-off-by: Srinivasan Shanmugam <srinivasan.shanmugam at amd.com>
Suggested-by: Alex Deucher <alexander.deucher at amd.com>
---
v2:
 - Incorporated feedbacks for function descriptions (Alex)

 drivers/gpu/drm/amd/amdgpu/amdgpu_gfx.c | 29 +++++++++++++++++++++++++
 1 file changed, 29 insertions(+)

diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_gfx.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_gfx.c
index e54f42e3797e..b1b133affbf9 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_gfx.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_gfx.c
@@ -1940,6 +1940,17 @@ void amdgpu_gfx_enforce_isolation_handler(struct work_struct *work)
 	mutex_unlock(&adev->enforce_isolation_mutex);
 }
 
+/**
+ * amdgpu_gfx_enforce_isolation_wait_for_kfd - Manage KFD wait period for process isolation
+ * @adev: amdgpu_device pointer
+ * @idx: Index of the GPU partition
+ *
+ * When kernel submissions come in, the jobs are given a time slice and once
+ * that time slice is up, if there are KFD user queues active, kernel
+ * submissions are blocked until KFD has had its time slice. Once the KFD time
+ * slice is up, KFD user queues are preempted and kernel submissions are
+ * unblocked and allowed to run again.
+ */
 static void
 amdgpu_gfx_enforce_isolation_wait_for_kfd(struct amdgpu_device *adev,
 					  u32 idx)
@@ -1985,6 +1996,15 @@ amdgpu_gfx_enforce_isolation_wait_for_kfd(struct amdgpu_device *adev,
 		msleep(GFX_SLICE_PERIOD_MS);
 }
 
+/**
+ * amdgpu_gfx_enforce_isolation_ring_begin_use - Begin use of a ring with enforced isolation
+ * @ring: Pointer to the amdgpu_ring structure
+ *
+ * Ring begin_use helper implementation for gfx which serializes access to the
+ * gfx IP between kernel submission IOCTLs and KFD user queues when isolation
+ * enforcement is enabled. The kernel submission IOCTLs and KFD user queues
+ * each get a time slice when both are active.
+ */
 void amdgpu_gfx_enforce_isolation_ring_begin_use(struct amdgpu_ring *ring)
 {
 	struct amdgpu_device *adev = ring->adev;
@@ -2012,6 +2032,15 @@ void amdgpu_gfx_enforce_isolation_ring_begin_use(struct amdgpu_ring *ring)
 	mutex_unlock(&adev->enforce_isolation_mutex);
 }
 
+/**
+ * amdgpu_gfx_enforce_isolation_ring_end_use - End use of a ring with enforced isolation
+ * @ring: Pointer to the amdgpu_ring structure
+ *
+ * Ring end_use helper implementation for gfx which serializes access to the
+ * gfx IP between kernel submission IOCTLs and KFD user queues when isolation
+ * enforcement is enabled. The kernel submission IOCTLs and KFD user queues
+ * each get a time slice when both are active.
+ */
 void amdgpu_gfx_enforce_isolation_ring_end_use(struct amdgpu_ring *ring)
 {
 	struct amdgpu_device *adev = ring->adev;
-- 
2.34.1