amdgpu only uses shared-fences internally, but dmabuf importers rely on implicit write hazard tracking via the reservation_object.fence_excl. For example, the importer use the write hazard for timing a page flip to only occur after the exporter has finished flushing its write into the surface. As such, on exporting a dmabuf, we must either flush all outstanding fences (for we do not know which are writes and should have been exclusive) or alternatively create a new exclusive fence that is the composite of all the existing shared fences, and so will only be signaled when all earlier fences are signaled (ensuring that we can not be signaled before the completion of any earlier write).
v2: reservation_object is already locked by amdgpu_bo_reserve() v3: Replace looping with get_fences_rcu and special case the promotion of a single shared fence directly to an exclusive fence, bypassing the fence array. v4: Drop the fence array ref after assigning to reservation_object
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=107341 Testcase: igt/amd_prime/amd-to-i915 References: 8e94a46c1770 ("drm/amdgpu: Attach exclusive fence to prime exported bo's. (v5)") Signed-off-by: Chris Wilson chris@chris-wilson.co.uk Cc: Alex Deucher alexander.deucher@amd.com Cc: "Christian König" christian.koenig@amd.com Reviewed-by: "Christian König" christian.koenig@amd.com --- drivers/gpu/drm/amd/amdgpu/amdgpu_prime.c | 59 ++++++++++++++++++++--- 1 file changed, 51 insertions(+), 8 deletions(-)
diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_prime.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_prime.c index 3fdd5688da0b..0394f5c77f81 100644 --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_prime.c +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_prime.c @@ -37,6 +37,7 @@ #include "amdgpu_display.h" #include <drm/amdgpu_drm.h> #include <linux/dma-buf.h> +#include <linux/dma-fence-array.h>
static const struct dma_buf_ops amdgpu_dmabuf_ops;
@@ -188,6 +189,48 @@ amdgpu_gem_prime_import_sg_table(struct drm_device *dev, return ERR_PTR(ret); }
+static int +__reservation_object_make_exclusive(struct reservation_object *obj) +{ + struct dma_fence **fences; + unsigned int count; + int r; + + if (!reservation_object_get_list(obj)) /* no shared fences to convert */ + return 0; + + r = reservation_object_get_fences_rcu(obj, NULL, &count, &fences); + if (r) + return r; + + if (count == 0) { + /* Now that was unexpected. */ + } else if (count == 1) { + reservation_object_add_excl_fence(obj, fences[0]); + dma_fence_put(fences[0]); + kfree(fences); + } else { + struct dma_fence_array *array; + + array = dma_fence_array_create(count, fences, + dma_fence_context_alloc(1), 0, + false); + if (!array) + goto err_fences_put; + + reservation_object_add_excl_fence(obj, &array->base); + dma_fence_put(&array->base); + } + + return 0; + +err_fences_put: + while (count--) + dma_fence_put(fences[count]); + kfree(fences); + return -ENOMEM; +} + /** * amdgpu_gem_map_attach - &dma_buf_ops.attach implementation * @dma_buf: shared DMA buffer @@ -219,16 +262,16 @@ static int amdgpu_gem_map_attach(struct dma_buf *dma_buf,
if (attach->dev->driver != adev->dev->driver) { /* - * Wait for all shared fences to complete before we switch to future - * use of exclusive fence on this prime shared bo. + * We only create shared fences for internal use, but importers + * of the dmabuf rely on exclusive fences for implicitly + * tracking write hazards. As any of the current fences may + * correspond to a write, we need to convert all existing + * fences on the reservation object into a single exclusive + * fence. */ - r = reservation_object_wait_timeout_rcu(bo->tbo.resv, - true, false, - MAX_SCHEDULE_TIMEOUT); - if (unlikely(r < 0)) { - DRM_DEBUG_PRIME("Fence wait failed: %li\n", r); + r = __reservation_object_make_exclusive(bo->tbo.resv); + if (r) goto error_unreserve; - } }
/* pin buffer into GTT */