A few fixes for a potential RPTR corruption issue.
Signed-off-by: Dave Airlie <airlied@redhat.com>
From: Rob Clark <robdclark@gmail.com>
Link: https://patchwork.freedesktop.org/patch/msgid/ <CAF6AEGvnr6Nhz2J0sjv2G+j7iceVtaDiJDT8T88uW6jiBfOGKQ@mail.gmail.com