[Intel-gfx] [PATCH v3 11/28] drm/i915: Add IRQ friendly request deference facility

[John.C.Harrison at Intel.com]

From: John Harrison <John.C.Harrison at Intel.com>

The next patches in the series convert some display related seqno usage to
request structure usage. However, the request dereference introduced must be
done from interrupt context. As the dereference potentially involves freeing the
request structure and thus calling lots of non-interrupt friendly code, this
poses a problem.

The solution is to add an IRQ friendly version of the dereference function. All
this does is to add the request structure to a 'delayed free' list and return.
The retire code, which is run periodically, then processes this list and does
the actual dereferencing of the request structures.

v2: Added a count to allow for multiple IRQ dereferences of the same request at
a time.

For: VIZ-4377
Signed-off-by: John Harrison <John.C.Harrison at Intel.com>
Reviewed-by: Thomas Daniel <Thomas.Daniel at intel.com>
---
 drivers/gpu/drm/i915/i915_drv.h         |    7 +++++++
 drivers/gpu/drm/i915/i915_gem.c         |   33 +++++++++++++++++++++++++++++++
 drivers/gpu/drm/i915/intel_lrc.c        |    2 ++
 drivers/gpu/drm/i915/intel_ringbuffer.c |    2 ++
 drivers/gpu/drm/i915/intel_ringbuffer.h |    2 ++
 5 files changed, 46 insertions(+)

diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
index 149532e6..e9b01e1 100644
--- a/drivers/gpu/drm/i915/i915_drv.h
+++ b/drivers/gpu/drm/i915/i915_drv.h
@@ -2025,6 +2025,10 @@ struct drm_i915_gem_request {
 	struct drm_i915_file_private *file_priv;
 	/** file_priv list entry for this request */
 	struct list_head client_list;
+
+	/** deferred free list for dereferencing from IRQ context */
+	struct list_head delay_free_list;
+	uint32_t delay_free_count;
 };
 
 void i915_gem_request_free(struct kref *req_ref);
@@ -2050,9 +2054,12 @@ i915_gem_request_reference(struct drm_i915_gem_request *req)
 static inline void
 i915_gem_request_unreference(struct drm_i915_gem_request *req)
 {
+	WARN_ON(!mutex_is_locked(&req->ring->dev->struct_mutex));
 	kref_put(&req->ref, i915_gem_request_free);
 }
 
+void i915_gem_request_unreference_irq(struct drm_i915_gem_request *req);
+
 static inline void i915_gem_request_assign(struct drm_i915_gem_request **pdst,
 					   struct drm_i915_gem_request *src)
 {
diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
index 8e2c530..b62b9d9 100644
--- a/drivers/gpu/drm/i915/i915_gem.c
+++ b/drivers/gpu/drm/i915/i915_gem.c
@@ -2732,6 +2732,19 @@ void i915_gem_reset(struct drm_device *dev)
 	i915_gem_restore_fences(dev);
 }
 
+void i915_gem_request_unreference_irq(struct drm_i915_gem_request *req)
+{
+	struct intel_engine_cs *ring = req->ring;
+	unsigned long flags;
+
+	/* Need to add the req to a deferred dereference list to be processed
+	 * outside of interrupt time */
+	spin_lock_irqsave(&ring->reqlist_lock, flags);
+	if (req->delay_free_count++ == 0)
+		list_add_tail(&req->delay_free_list, &ring->delayed_free_list);
+	spin_unlock_irqrestore(&ring->reqlist_lock, flags);
+}
+
 /**
  * This function clears the request list as sequence numbers are passed.
  */
@@ -2806,6 +2819,25 @@ i915_gem_retire_requests_ring(struct intel_engine_cs *ring)
 		ring->trace_irq_seqno = 0;
 	}
 
+	while (!list_empty(&ring->delayed_free_list)) {
+		struct drm_i915_gem_request *request;
+		unsigned long flags;
+		uint32_t count;
+
+		request = list_first_entry(&ring->delayed_free_list,
+					   struct drm_i915_gem_request,
+					   delay_free_list);
+
+		spin_lock_irqsave(&request->ring->reqlist_lock, flags);
+		list_del(&request->delay_free_list);
+		count = request->delay_free_count;
+		request->delay_free_count = 0;
+		spin_unlock_irqrestore(&request->ring->reqlist_lock, flags);
+
+		while (count-- > 0)
+			i915_gem_request_unreference(request);
+	}
+
 	WARN_ON(i915_verify_lists(ring->dev));
 }
 
@@ -5007,6 +5039,7 @@ init_ring_lists(struct intel_engine_cs *ring)
 {
 	INIT_LIST_HEAD(&ring->active_list);
 	INIT_LIST_HEAD(&ring->request_list);
+	INIT_LIST_HEAD(&ring->delayed_free_list);
 }
 
 void i915_init_vm(struct drm_i915_private *dev_priv,
diff --git a/drivers/gpu/drm/i915/intel_lrc.c b/drivers/gpu/drm/i915/intel_lrc.c
index 6177179..09f4588 100644
--- a/drivers/gpu/drm/i915/intel_lrc.c
+++ b/drivers/gpu/drm/i915/intel_lrc.c
@@ -1381,7 +1381,9 @@ static int logical_ring_init(struct drm_device *dev, struct intel_engine_cs *rin
 	ring->dev = dev;
 	INIT_LIST_HEAD(&ring->active_list);
 	INIT_LIST_HEAD(&ring->request_list);
+	spin_lock_init(&ring->reqlist_lock);
 	init_waitqueue_head(&ring->irq_queue);
+	INIT_LIST_HEAD(&ring->delayed_free_list);
 
 	INIT_LIST_HEAD(&ring->execlist_queue);
 	INIT_LIST_HEAD(&ring->execlist_retired_req_list);
diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.c b/drivers/gpu/drm/i915/intel_ringbuffer.c
index b9d0d29..e3082af 100644
--- a/drivers/gpu/drm/i915/intel_ringbuffer.c
+++ b/drivers/gpu/drm/i915/intel_ringbuffer.c
@@ -1807,6 +1807,8 @@ static int intel_init_ring_buffer(struct drm_device *dev,
 	ring->dev = dev;
 	INIT_LIST_HEAD(&ring->active_list);
 	INIT_LIST_HEAD(&ring->request_list);
+	spin_lock_init(&ring->reqlist_lock);
+	INIT_LIST_HEAD(&ring->delayed_free_list);
 	INIT_LIST_HEAD(&ring->execlist_queue);
 	ringbuf->size = 32 * PAGE_SIZE;
 	ringbuf->ring = ring;
diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.h b/drivers/gpu/drm/i915/intel_ringbuffer.h
index 2a84bd9..cd1a9f9 100644
--- a/drivers/gpu/drm/i915/intel_ringbuffer.h
+++ b/drivers/gpu/drm/i915/intel_ringbuffer.h
@@ -263,6 +263,8 @@ struct  intel_engine_cs {
 	 * outstanding.
 	 */
 	struct list_head request_list;
+	spinlock_t reqlist_lock;
+	struct list_head delayed_free_list;
 
 	/**
 	 * Do we have some not yet emitted requests outstanding?
-- 
1.7.9.5