[PATCH] drm/amdgpu: add ih waiter on process until checkpoint

[Jonathan Kim]

Add IH function to allow caller to wait until ring entries are processed
until the checkpoint write pointer.

This will be primarily used by HMM to drain pending page fault interrupts
before memory unmap to prevent HMM from handling stale interrupts.

v3: Scrap busy loop and change to wait_event.

v2: Update title and description to clarify use.
Add rptr/wptr wrap counter checks to guarantee ring entries are processed
until the checkpoint.

Suggested-by: Christian Koenig <christian.koenig at amd.com>
Signed-off-by: Jonathan Kim <jonathan.kim at amd.com>
---
 drivers/gpu/drm/amd/amdgpu/amdgpu_ih.c | 49 ++++++++++++++++++++++++++
 drivers/gpu/drm/amd/amdgpu/amdgpu_ih.h |  5 +++
 2 files changed, 54 insertions(+)

diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_ih.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_ih.c
index dc852af4f3b7..1024065f1f03 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_ih.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_ih.c
@@ -99,6 +99,8 @@ int amdgpu_ih_ring_init(struct amdgpu_device *adev, struct amdgpu_ih_ring *ih,
 		ih->rptr_addr = adev->wb.gpu_addr + rptr_offs * 4;
 		ih->rptr_cpu = &adev->wb.wb[rptr_offs];
 	}
+
+	init_waitqueue_head(&ih->wait_process);
 	return 0;
 }
 
@@ -160,6 +162,52 @@ void amdgpu_ih_ring_write(struct amdgpu_ih_ring *ih, const uint32_t *iv,
 	}
 }
 
+/* Waiter helper that checks current rptr matches or passes checkpoint wptr */
+static bool amdgpu_ih_has_checkpoint_processed(struct amdgpu_device *adev,
+					struct amdgpu_ih_ring *ih,
+					uint32_t checkpoint_wptr,
+					uint32_t *prev_rptr)
+{
+	uint32_t cur_rptr = ih->rptr | (*prev_rptr & ~ih->ptr_mask);
+
+	/* rptr has wrapped. */
+	if (cur_rptr < *prev_rptr)
+		cur_rptr += ih->ptr_mask + 1;
+	*prev_rptr = cur_rptr;
+
+	return cur_rptr >= checkpoint_wptr;
+}
+
+/**
+ * amdgpu_ih_wait_on_checkpoint_process - wait to process IVs up to checkpoint
+ *
+ * @adev: amdgpu_device pointer
+ * @ih: ih ring to process
+ *
+ * Used to ensure ring has processed IVs up to the checkpoint write pointer.
+ */
+int amdgpu_ih_wait_on_checkpoint_process(struct amdgpu_device *adev,
+					struct amdgpu_ih_ring *ih)
+{
+	uint32_t checkpoint_wptr, rptr;
+
+	if (!ih->enabled || adev->shutdown)
+		return -ENODEV;
+
+	checkpoint_wptr = amdgpu_ih_get_wptr(adev, ih);
+	/* Order wptr with rptr. */
+	rmb();
+	rptr = READ_ONCE(ih->rptr);
+
+	/* wptr has wrapped. */
+	if (rptr > checkpoint_wptr)
+		checkpoint_wptr += ih->ptr_mask + 1;
+
+	return wait_event_interruptible(ih->wait_process,
+				amdgpu_ih_has_checkpoint_processed(adev, ih,
+						checkpoint_wptr, &rptr));
+}
+
 /**
  * amdgpu_ih_process - interrupt handler
  *
@@ -195,6 +243,7 @@ int amdgpu_ih_process(struct amdgpu_device *adev, struct amdgpu_ih_ring *ih)
 	}
 
 	amdgpu_ih_set_rptr(adev, ih);
+	wake_up_all(&ih->wait_process);
 	atomic_set(&ih->lock, 0);
 
 	/* make sure wptr hasn't changed while processing */
diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_ih.h b/drivers/gpu/drm/amd/amdgpu/amdgpu_ih.h
index 6ed4a85fc7c3..87ec6d20dbe0 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_ih.h
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_ih.h
@@ -66,6 +66,9 @@ struct amdgpu_ih_ring {
 	unsigned		rptr;
 	atomic_t		lock;
 	struct amdgpu_ih_regs	ih_regs;
+
+	/* For waiting on IH processing at checkpoint. */
+	wait_queue_head_t wait_process;
 };
 
 /* provided by the ih block */
@@ -87,6 +90,8 @@ int amdgpu_ih_ring_init(struct amdgpu_device *adev, struct amdgpu_ih_ring *ih,
 void amdgpu_ih_ring_fini(struct amdgpu_device *adev, struct amdgpu_ih_ring *ih);
 void amdgpu_ih_ring_write(struct amdgpu_ih_ring *ih, const uint32_t *iv,
 			  unsigned int num_dw);
+int amdgpu_ih_wait_on_checkpoint_process(struct amdgpu_device *adev,
+					struct amdgpu_ih_ring *ih);
 int amdgpu_ih_process(struct amdgpu_device *adev, struct amdgpu_ih_ring *ih);
 void amdgpu_ih_decode_iv_helper(struct amdgpu_device *adev,
 				struct amdgpu_ih_ring *ih,
-- 
2.17.1