drm/i915: Avoid using the i915_fence_array when collecting dependencies

Since the gt migration code was using only a single fence for
dependencies, these were collected in a dma_fence_array. However, it
turns out that it's illegal to use some dma_fences in a dma_fence_array,
in particular other dma_fence_arrays and dma_fence_chains, and this
causes trouble for us moving forward.

Have the gt migration code instead take a const struct i915_deps for
dependencies. This means we can skip the dma_fence_array creation
and instead pass the struct i915_deps instead to circumvent the
problem.

v2:
- Make the prev_deps() function static. (kernel test robot <lkp@intel.com>)
- Update the struct i915_deps kerneldoc.
v4:
- Rebase.

Fixes: 5652df829b3c ("drm/i915/ttm: Update i915_gem_obj_copy_ttm() to be asynchronous")
Signed-off-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Reviewed-by: Matthew Auld <matthew.auld@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20211221200050.436316-2-thomas.hellstrom@linux.intel.com

1 files changed, 22 insertions, 0 deletions

diff --git a/drivers/gpu/drm/i915/i915_request.c b/drivers/gpu/drm/i915/i915_request.c
index fe682b6902aa..a18aae4891c0 100644
--- a/drivers/gpu/drm/i915/i915_request.c
+++ b/drivers/gpu/drm/i915/i915_request.c
@@ -31,6 +31,7 @@
 #include <linux/sched/signal.h>
 
 #include "gem/i915_gem_context.h"
+#include "gem/i915_gem_ttm_move.h"
 #include "gt/intel_breadcrumbs.h"
 #include "gt/intel_context.h"
 #include "gt/intel_engine.h"
@@ -1543,6 +1544,27 @@ i915_request_await_dma_fence(struct i915_request *rq, struct dma_fence *fence)
 }
 
 /**
+ * i915_request_await_deps - set this request to (async) wait upon a struct
+ * i915_deps dma_fence collection
+ * @rq: request we are wishing to use
+ * @deps: The struct i915_deps containing the dependencies.
+ *
+ * Returns 0 if successful, negative error code on error.
+ */
+int i915_request_await_deps(struct i915_request *rq, const struct i915_deps *deps)
+{
+	int i, err;
+
+	for (i = 0; i < deps->num_deps; ++i) {
+		err = i915_request_await_dma_fence(rq, deps->fences[i]);
+		if (err)
+			return err;
+	}
+
+	return 0;
+}
+
+/**
  * i915_request_await_object - set this request to (async) wait upon a bo
  * @to: request we are wishing to use
  * @obj: object which may be in use on another ring.