drm/i915/guc: Ensure request ordering via completion fences
If two requests are on the same ring, they are explicitly ordered by the HW. So, a submission fence is sufficient to ensure ordering when using the new GuC submission interface. Conversely, if two requests share a timeline and are on the same physical engine but different context this doesn't ensure ordering on the new GuC submission interface. So, a completion fence needs to be used to ensure ordering. v2: (Daniele) - Don't delete spin lock v3: (Daniele) - Delete forward dec Signed-off-by: John Harrison <John.C.Harrison@Intel.com> Signed-off-by: Matthew Brost <matthew.brost@intel.com> Reviewed-by: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com> Signed-off-by: John Harrison <John.C.Harrison@Intel.com> Link: https://patchwork.freedesktop.org/patch/msgid/20210721215101.139794-13-matthew.brost@intel.com
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