drm/ttm: rework pipelined eviction fence handling

Until now ttm stored a single pipelined eviction fence which means
drivers had to use a single entity for these evictions.

To lift this requirement, this commit allows up to 8 entities to
be used.

Ideally a dma_resv object would have been used as a container of
the eviction fences, but the locking rules makes it complex.
dma_resv all have the same ww_class, which means "Attempting to
lock more mutexes after ww_acquire_done." is an error.

One alternative considered was to introduced a 2nd ww_class for
specific resv to hold a single "transient" lock (= the resv lock
would only be held for a short period, without taking any other
locks).

The other option, is to statically reserve a fence array, and
extend the existing code to deal with N fences, instead of 1.

The driver is still responsible to reserve the correct number
of fence slots.

Signed-off-by: Pierre-Eric Pelloux-Prayer <pierre-eric.pelloux-prayer@amd.com>
Link: https://lore.kernel.org/r/20251121101315.3585-20-pierre-eric.pelloux-prayer@amd.com
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Christian König <christian.koenig@amd.com>

1 files changed, 24 insertions, 23 deletions

diff --git a/drivers/gpu/drm/ttm/ttm_bo.c b/drivers/gpu/drm/ttm/ttm_bo.c
index c4e669686fd6..bd27607f8076 100644
--- a/drivers/gpu/drm/ttm/ttm_bo.c
+++ b/drivers/gpu/drm/ttm/ttm_bo.c
@@ -659,34 +659,35 @@ void ttm_bo_unpin(struct ttm_buffer_object *bo)
 EXPORT_SYMBOL(ttm_bo_unpin);
 
 /*
- * Add the last move fence to the BO as kernel dependency and reserve a new
- * fence slot.
+ * Add the pipelined eviction fencesto the BO as kernel dependency and reserve new
+ * fence slots.
  */
-static int ttm_bo_add_move_fence(struct ttm_buffer_object *bo,
-				 struct ttm_resource_manager *man,
-				 bool no_wait_gpu)
+static int ttm_bo_add_pipelined_eviction_fences(struct ttm_buffer_object *bo,
+						struct ttm_resource_manager *man,
+						bool no_wait_gpu)
 {
 	struct dma_fence *fence;
-	int ret;
-
-	spin_lock(&man->move_lock);
-	fence = dma_fence_get(man->move);
-	spin_unlock(&man->move_lock);
+	int i;
 
-	if (!fence)
-		return 0;
+	spin_lock(&man->eviction_lock);
+	for (i = 0; i < TTM_NUM_MOVE_FENCES; i++) {
+		fence = man->eviction_fences[i];
+		if (!fence)
+			continue;
 
-	if (no_wait_gpu) {
-		ret = dma_fence_is_signaled(fence) ? 0 : -EBUSY;
-		dma_fence_put(fence);
-		return ret;
+		if (no_wait_gpu) {
+			if (!dma_fence_is_signaled(fence)) {
+				spin_unlock(&man->eviction_lock);
+				return -EBUSY;
+			}
+		} else {
+			dma_resv_add_fence(bo->base.resv, fence, DMA_RESV_USAGE_KERNEL);
+		}
 	}
+	spin_unlock(&man->eviction_lock);
 
-	dma_resv_add_fence(bo->base.resv, fence, DMA_RESV_USAGE_KERNEL);
-
-	ret = dma_resv_reserve_fences(bo->base.resv, 1);
-	dma_fence_put(fence);
-	return ret;
+	/* TODO: this call should be removed. */
+	return dma_resv_reserve_fences(bo->base.resv, 1);
 }
 
 /**
@@ -719,7 +720,7 @@ static int ttm_bo_alloc_resource(struct ttm_buffer_object *bo,
 	int i, ret;
 
 	ticket = dma_resv_locking_ctx(bo->base.resv);
-	ret = dma_resv_reserve_fences(bo->base.resv, 1);
+	ret = dma_resv_reserve_fences(bo->base.resv, TTM_NUM_MOVE_FENCES);
 	if (unlikely(ret))
 		return ret;
 
@@ -758,7 +759,7 @@ static int ttm_bo_alloc_resource(struct ttm_buffer_object *bo,
 				return ret;
 		}
 
-		ret = ttm_bo_add_move_fence(bo, man, ctx->no_wait_gpu);
+		ret = ttm_bo_add_pipelined_eviction_fences(bo, man, ctx->no_wait_gpu);
 		if (unlikely(ret)) {
 			ttm_resource_free(bo, res);
 			if (ret == -EBUSY)