EHCI driver accesses mmio space using regular struct pointers. In order to avoid
any CPU re-ordering, memory barrier is required in async_set_schedule,
especially for arm64. Without the memory barrier, there seems to be re-ordering
taking place which leads to USB errors with some flash drives as well as
transfer errors in netboot.
BUG=chrome-os-partner:31533
BRANCH=None
TEST=With the memory barrier introduced, netboot for ryu completes transfer
without any error and finishes within 6-7 seconds.
Change-Id: Ic05d47422312a1cddbebe3180f4f159853604440
Signed-off-by: Furquan Shaikh <furquan@google.com>
Reviewed-on: https://chromium-review.googlesource.com/213917
Reviewed-by: Aaron Durbin <adurbin@chromium.org>
Tested-by: Furquan Shaikh <furquan@chromium.org>
Commit-Queue: Furquan Shaikh <furquan@chromium.org>
561bdd746c