[Intel-gfx] [PATCH] drm/i915: remove questionable fence optimization during copy

[Christian König]

First of all as discussed multiple times now kernel copies *must* always wait
for all fences in a BO before actually doing the copy. This is mandatory.

Additional to that drop the handling when there can't be a shared slot
allocated on the source BO and just properly return an error code. Otherwise
this code path would only be tested under out of memory conditions.

Signed-off-by: Christian König <christian.koe...@amd.com>
---
 drivers/gpu/drm/i915/gem/i915_gem_ttm_move.c | 39 +++++++-------------
 1 file changed, 14 insertions(+), 25 deletions(-)

diff --git a/drivers/gpu/drm/i915/gem/i915_gem_ttm_move.c 
b/drivers/gpu/drm/i915/gem/i915_gem_ttm_move.c
index 80df9f592407..798f310d710c 100644
--- a/drivers/gpu/drm/i915/gem/i915_gem_ttm_move.c
+++ b/drivers/gpu/drm/i915/gem/i915_gem_ttm_move.c
@@ -250,19 +250,14 @@ static struct dma_fence *i915_deps_to_fence(struct 
i915_deps *deps,
 }
 
 static int i915_deps_add_resv(struct i915_deps *deps, struct dma_resv *resv,
-                             bool all, const bool no_excl,
                              const struct ttm_operation_ctx *ctx)
 {
        struct dma_resv_iter iter;
        struct dma_fence *fence;
+       int ret;
 
        dma_resv_assert_held(resv);
-       dma_resv_for_each_fence(&iter, resv, all, fence) {
-               int ret;
-
-               if (no_excl && dma_resv_iter_is_exclusive(&iter))
-                       continue;
-
+       dma_resv_for_each_fence(&iter, resv, true, fence) {
                ret = i915_deps_add_dependency(deps, fence, ctx);
                if (ret)
                        return ret;
@@ -698,7 +693,7 @@ static struct dma_fence *prev_fence(struct 
ttm_buffer_object *bo,
                 * TODO: Only await excl fence here, and shared fences before
                 * signaling the migration fence.
                 */
-               ret = i915_deps_add_resv(&deps, bo->base.resv, true, false, 
ctx);
+               ret = i915_deps_add_resv(&deps, bo->base.resv, ctx);
        if (ret)
                return ERR_PTR(ret);
 
@@ -828,22 +823,21 @@ int i915_gem_obj_copy_ttm(struct drm_i915_gem_object *dst,
        struct i915_refct_sgt *dst_rsgt;
        struct dma_fence *copy_fence, *dep_fence;
        struct i915_deps deps;
-       int ret, shared_err;
+       int ret;
 
        assert_object_held(dst);
        assert_object_held(src);
        i915_deps_init(&deps, GFP_KERNEL | __GFP_NORETRY | __GFP_NOWARN);
 
-       /*
-        * We plan to add a shared fence only for the source. If that
-        * fails, we await all source fences before commencing
-        * the copy instead of only the exclusive.
-        */
-       shared_err = dma_resv_reserve_shared(src_bo->base.resv, 1);
-       ret = i915_deps_add_resv(&deps, dst_bo->base.resv, true, false, &ctx);
-       if (!ret)
-               ret = i915_deps_add_resv(&deps, src_bo->base.resv,
-                                        !!shared_err, false, &ctx);
+       ret = dma_resv_reserve_shared(src_bo->base.resv, 1);
+       if (ret)
+               return ret;
+
+       ret = i915_deps_add_resv(&deps, dst_bo->base.resv, &ctx);
+       if (ret)
+               return ret;
+
+       ret = i915_deps_add_resv(&deps, src_bo->base.resv, &ctx);
        if (ret)
                return ret;
 
@@ -861,12 +855,7 @@ int i915_gem_obj_copy_ttm(struct drm_i915_gem_object *dst,
                return PTR_ERR_OR_ZERO(copy_fence);
 
        dma_resv_add_excl_fence(dst_bo->base.resv, copy_fence);
-
-       /* If we failed to reserve a shared slot, add an exclusive fence */
-       if (shared_err)
-               dma_resv_add_excl_fence(src_bo->base.resv, copy_fence);
-       else
-               dma_resv_add_shared_fence(src_bo->base.resv, copy_fence);
+       dma_resv_add_shared_fence(src_bo->base.resv, copy_fence);
 
        dma_fence_put(copy_fence);
 
-- 
2.25.1