On Thu, Sep 28, 2017 at 3:11 PM, Sudeep Holla [off-list ref] wrote:

Some of the mailbox controller expects controller specific data in order
to implement simple doorbell mechanism as expected by SCMI specification.

This patch creates a shim layer to abstract the mailbox interface so
that it can support any mailbox controller. It also provides default
implementation which maps to standard mailbox client APIs, so that
controllers implementing doorbell mechanism need not require any
additional layer.

Cc: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Sudeep Holla <redacted>

Another level? Now we have three levels of stacked mailboxes, with
the highest level being the combined mailbox/memory, then the shim,
and below it the hardware mailbox.

Can you try to come up with a way to do this with fewer abstractions?

Maybe you could assume that the mailbox itself can take variable-length
data packets, and then use the shim here for those that require
something else?

        Arnd