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, 2 insertions, 0 deletions

diff --git a/drivers/gpu/drm/i915/i915_request.h b/drivers/gpu/drm/i915/i915_request.h
index ce7714210697..170ee78c2858 100644
--- a/drivers/gpu/drm/i915/i915_request.h
+++ b/drivers/gpu/drm/i915/i915_request.h
@@ -47,6 +47,7 @@
 struct drm_file;
 struct drm_i915_gem_object;
 struct drm_printer;
+struct i915_deps;
 struct i915_request;
 
 #if IS_ENABLED(CONFIG_DRM_I915_CAPTURE_ERROR)
@@ -411,6 +412,7 @@ int i915_request_await_object(struct i915_request *to,
 			      bool write);
 int i915_request_await_dma_fence(struct i915_request *rq,
 				 struct dma_fence *fence);
+int i915_request_await_deps(struct i915_request *rq, const struct i915_deps *deps);
 int i915_request_await_execution(struct i915_request *rq,
 				 struct dma_fence *fence);