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morello: Enforce strict ordering for mailbox memory

Darryl Green requested to merge github/fork/anukou/master into master

Created by: anukou

The mailbox memory is shared between the SCP and the OSPM agent, and is used for SCMI communication between the two. The underlying memory region, which the mailbox memory is mapped to, is currently configured as Normal Memory (weak ordering) via the SCP MPU attributes.

This has been traced down to be the origin of the occasional mailbox channel ownership errors as seen in the SCP FW logs - the root cause being that on some occasions, the firmware ends up reading the stale value of the channel ownership status bit (as opposed to the reading value updated by the SCMI agent during the SCMI comms) because of the reordering/buffering at the interconnect.

Configuring the memory region to Strongly Ordered enforces a strict ordering and gets rid of the mailbox channel ownership errors.

Signed-off-by: Anurag Koul anurag.koul@arm.com Change-Id: I69b2f74e111dde1b7d1e0a22ba85f101366eb86d

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