[PATCH 0/2] mailbox: arm: introduce smc triggered mailbox

[Peng Fan]

This is a modified version from Andre Przywara's patch series
https://lore.kernel.org/patchwork/cover/812997/.
[1] is a draft implementation of i.MX8MM SCMI ATF implementation that
use smc as mailbox, power/clk is included, but only part of clk has been
implemented to work with hardware, power domain only supports get name
for now.

The traditional Linux mailbox mechanism uses some kind of dedicated hardware
IP to signal a condition to some other processing unit, typically a dedicated
management processor.
This mailbox feature is used for instance by the SCMI protocol to signal a
request for some action to be taken by the management processor.
However some SoCs does not have a dedicated management core to provide
those services. In order to service TEE and to avoid linux shutdown
power and clock that used by TEE, need let firmware to handle power
and clock, the firmware here is ARM Trusted Firmware that could also
run SCMI service.

The existing SCMI implementation uses a rather flexible shared memory
region to communicate commands and their parameters, it still requires a
mailbox to actually trigger the action.

This patch series provides a Linux mailbox compatible service which uses
smc calls to invoke firmware code, for instance taking care of SCMI requests.
The actual requests are still communicated using the standard SCMI way of
shared memory regions, but a dedicated mailbox hardware IP can be replaced via
this new driver.

This simple driver uses the architected SMC calling convention to trigger
firmware services, also allows for using "HVC" calls to call into hypervisors
or firmware layers running in the EL2 exception level.

Patch 1 contains the device tree binding documentation, patch 2 introduces
the actual mailbox driver.

Please note that this driver just provides a generic mailbox mechanism,
though this is synchronous and one-way only (triggered by the OS only,
without providing an asynchronous way of triggering request from the
firmware).
And while providing SCMI services was the reason for this exercise, this
driver is in no way bound to this use case, but can be used generically
where the OS wants to signal a mailbox condition to firmware or a
hypervisor.
Also the driver is in no way meant to replace any existing firmware
interface, but actually to complement existing interfaces.

[1] https://github.com/MrVan/arm-trusted-firmware/tree/scmi

Peng Fan (2):
  DT: mailbox: add binding doc for the ARM SMC mailbox
  mailbox: introduce ARM SMC based mailbox

 .../devicetree/bindings/mailbox/arm-smc.txt        |  96 +++++++++++++
 drivers/mailbox/Kconfig                            |   7 +
 drivers/mailbox/Makefile                           |   2 +
 drivers/mailbox/arm-smc-mailbox.c                  | 154 +++++++++++++++++++++
 include/linux/mailbox/arm-smc-mailbox.h            |  10 ++
 5 files changed, 269 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/mailbox/arm-smc.txt
 create mode 100644 drivers/mailbox/arm-smc-mailbox.c
 create mode 100644 include/linux/mailbox/arm-smc-mailbox.h

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2.16.4