Everyone who selects VIRTIO is also made to select VIRTIO_RING; just make
them synonymous, since we removed the indirection layer some time ago.
Signed-off-by: NRusty Russell <rusty@rustcorp.com.au>

There isn't any binary change in sight or evidence of any stability
issue, but as we just begin to get traction we can't rule them out
completely.

To be on the safe side, let's mark rpmsg as EXPERIMENTAL, and remove
it later on after we have several happy users.
Signed-off-by: NOhad Ben-Cohen <ohad@wizery.com>
Cc: Stephen Boyd <sboyd@codeaurora.org>
Cc: Rob Clark <rob@ti.com>
Cc: Mark Grosen <mgrosen@ti.com>
Cc: Ludovic BARRE <ludovic.barre@stericsson.com>

Add a dedicated Kconfig menu for the rpmsg drivers, so they
don't show up in the main driver menu.
Signed-off-by: NOhad Ben-Cohen <ohad@wizery.com>

Add a virtio-based inter-processor communication bus, which enables
kernel drivers to communicate with entities, running on remote
processors, over shared memory using a simple messaging protocol.

Every pair of AMP processors share two vrings, which are used to send
and receive the messages over shared memory.

The header of every message sent on the rpmsg bus contains src and dst
addresses, which make it possible to multiplex several rpmsg channels on
the same vring.

Every rpmsg channel is a device on this bus. When a channel is added,
and an appropriate rpmsg driver is found and probed, it is also assigned
a local rpmsg address, which is then bound to the driver's callback.

When inbound messages carry the local address of a bound driver,
its callback is invoked by the bus.

This patch provides a kernel interface only; user space interfaces
will be later exposed by kernel users of this rpmsg bus.

Designed with Brian Swetland <swetland@google.com>.
Signed-off-by: NOhad Ben-Cohen <ohad@wizery.com>
Acked-by: Rusty Russell <rusty@rustcorp.com.au> (virtio_ids.h)
Cc: Brian Swetland <swetland@google.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Grant Likely <grant.likely@secretlab.ca>
Cc: Tony Lindgren <tony@atomide.com>
Cc: Russell King <linux@arm.linux.org.uk>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Greg KH <greg@kroah.com>
Cc: Stephen Boyd <sboyd@codeaurora.org>