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Subject[PATCH 5/7] drm: Add helpers for setting up an array of dma_fence dependencies.
Date
I needed to add implicit dependency support for v3d, and Rob Herring
has been working on it for panfrost, and I had recently looked at the
lima implementation so I think this will be a good intersection of
what we all want and simplify our scheduler implementations.

Signed-off-by: Eric Anholt <eric@anholt.net>
---
drivers/gpu/drm/drm_gem.c | 94 +++++++++++++++++++++++++++++++++++++++
include/drm/drm_gem.h | 5 +++
2 files changed, 99 insertions(+)

diff --git a/drivers/gpu/drm/drm_gem.c b/drivers/gpu/drm/drm_gem.c
index 388b3742e562..7b3c73135e49 100644
--- a/drivers/gpu/drm/drm_gem.c
+++ b/drivers/gpu/drm/drm_gem.c
@@ -1311,3 +1311,97 @@ drm_gem_unlock_reservations(struct drm_gem_object **objs, int count,
ww_acquire_fini(acquire_ctx);
}
EXPORT_SYMBOL(drm_gem_unlock_reservations);
+
+/**
+ * drm_gem_fence_array_add - Adds the fence to an array of fences to be
+ * waited on, deduplicating fences from the same context.
+ *
+ * @fence_array array of dma_fence * for the job to block on.
+ * @fence the dma_fence to add to the list of dependencies.
+ *
+ * Returns:
+ * 0 on success, or an error on failing to expand the array.
+ */
+int drm_gem_fence_array_add(struct xarray *fence_array,
+ struct dma_fence *fence)
+{
+ struct dma_fence *entry;
+ unsigned long index;
+ u32 id = 0;
+ int ret;
+
+ if (!fence)
+ return 0;
+
+ /* Deduplicate if we already depend on a fence from the same context.
+ * This lets the size of the array of deps scale with the number of
+ * engines involved, rather than the number of BOs.
+ */
+ xa_for_each(fence_array, index, entry) {
+ if (entry->context != fence->context)
+ continue;
+
+ if (dma_fence_is_later(fence, entry)) {
+ dma_fence_put(entry);
+ xa_store(fence_array, index, fence, GFP_KERNEL);
+ } else {
+ dma_fence_put(fence);
+ }
+ return 0;
+ }
+
+ ret = xa_alloc(fence_array, &id, UINT_MAX, fence, GFP_KERNEL);
+ if (ret != 0)
+ dma_fence_put(fence);
+
+ return ret;
+}
+EXPORT_SYMBOL(drm_gem_fence_array_add);
+
+/**
+ * drm_gem_fence_array_add_implicit - Adds the implicit dependencies tracked
+ * in the GEM object's reservation object to an array of dma_fences for use in
+ * scheduling a rendering job.
+ *
+ * This should be called after drm_gem_lock_reservations() on your array of
+ * GEM objects used in the job but before updating the reservations with your
+ * own fences.
+ *
+ * @fence_array array of dma_fence * for the job to block on.
+ * @obj the gem object to add new dependencies from.
+ * @write whether the job might write the object (so we need to depend on
+ * shared fences in the reservation object).
+ */
+int drm_gem_fence_array_add_implicit(struct xarray *fence_array,
+ struct drm_gem_object *obj,
+ bool write)
+{
+ int ret;
+ struct dma_fence **fences;
+ unsigned i, fence_count;
+
+ if (!write) {
+ struct dma_fence *fence =
+ reservation_object_get_excl_rcu(obj->resv);
+
+ return drm_gem_fence_array_add(fence_array, fence);
+ }
+
+ ret = reservation_object_get_fences_rcu(obj->resv, NULL,
+ &fence_count, &fences);
+ if (ret || !fence_count)
+ return ret;
+
+ for (i = 0; i < fence_count; i++) {
+ ret = drm_gem_fence_array_add(fence_array, fences[i]);
+ if (ret)
+ break;
+ }
+
+ for (; i < fence_count; i++)
+ dma_fence_put(fences[i]);
+ kfree(fences);
+ return ret;
+}
+
+EXPORT_SYMBOL(drm_gem_fence_array_add_implicit);
diff --git a/include/drm/drm_gem.h b/include/drm/drm_gem.h
index 2955aaab3dca..e957753d3f94 100644
--- a/include/drm/drm_gem.h
+++ b/include/drm/drm_gem.h
@@ -388,6 +388,11 @@ int drm_gem_lock_reservations(struct drm_gem_object **objs, int count,
struct ww_acquire_ctx *acquire_ctx);
void drm_gem_unlock_reservations(struct drm_gem_object **objs, int count,
struct ww_acquire_ctx *acquire_ctx);
+int drm_gem_fence_array_add(struct xarray *fence_array,
+ struct dma_fence *fence);
+int drm_gem_fence_array_add_implicit(struct xarray *fence_array,
+ struct drm_gem_object *obj,
+ bool write);
int drm_gem_dumb_map_offset(struct drm_file *file, struct drm_device *dev,
u32 handle, u64 *offset);
int drm_gem_dumb_destroy(struct drm_file *file,
--
2.20.1
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