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This patch adds the driver to communicate with the BPMP firmware on Tegra
SoCs, starting Tegra186. BPMP firmware is responsible for clock enable/
disable requests, module resets among other things.

MRQ is short for Message ReQuest. This is the general purpose, multi channel
messaging protocol that is widely used to communicate with BPMP. This is further
divided into a common high level protocol and a peer-specific low level protocol.
The higher level protocol specifies the peer identification, channel definition
and allocation, message structure, message semantics and message dispatch process
whereas the lower level protocol defines actual message transfer implementation
details. Currently, BPMP supports two lower level protocols - Token Mail Operations
(TMO), IVC Mail Operations (IMO).

This driver implements the IMO protocol. IMO is implemented using the IVC (Inter-VM
Communication) protocol which is a lockless, shared memory messaging queue management
protocol.

The IVC peer is expected to perform the following as part of establishing a connection
with BPMP.

1. Initialize the channels with tegra_ivc_init() or its equivalent.
2. Reset the channel with tegra_ivc_channel_reset. The peer should also ensure that
   BPMP is notified via the doorbell.
3. Poll until the channel connection is established [tegra_ivc_channel_notified() return
   0]. Interrupt BPMP with doorbell each time after tegra_ivc_channel_notified() return
   non zero.

The IPC driver currently supports reseting the GPCDMAand XUSB_PADCTL hardware blocks. In
future, more hardware blocks would be supported.

Change-Id: I52a4bd3a853de6c4fa410904b6614ff1c63df364
Signed-off-by: Varun Wadekar <vwadekar@nvidia.com>