i3c: Make i3c_bus_type const

Since commit d492cc2573a0 ("driver core: device.h: make struct
bus_type a const *"), the driver core can properly handle constant
struct bus_type, move the i3c_bus_type variable to be a constant
structure as well, placing it into read-only memory which can not be
modified at runtime.

Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Suggested-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Ricardo B. Marliere <ricardo@marliere.net>
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Link: https://lore.kernel.org/r/20240213-bus_cleanup-i3c-v1-1-403aea18f05a@marliere.net
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>

i3c: export SETDASA method

Because not all I3C drivers have the hot-join feature ready, and
especially not all I3C devices support hot-join feature, exporting
SETDASA method could be useful. With this function, the I3C controller
could perform a DAA to I3C devices when users decide to turn these I3C
devices off and on again during run-time.

Tested: This change has been tested with turnning off an I3C device and
turning on it again during run-time. The device driver calls SETDASA
method to perform DAA to the device. And communication between I3C
controller and device is set up again correctly.

Signed-off-by: Jack Chen <zenghuchen@google.com>
Link: https://lore.kernel.org/r/20221207205059.3848851-1-zenghuchen@google.com
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>

i3c: Add core I3C infrastructure

Add core infrastructure to support I3C in Linux and document it.

This infrastructure adds basic I3C support. Advanced features will be
added afterwards.

There are a few design choices that are worth mentioning because they
impact the way I3C device drivers can interact with their devices:

- all functions used to send I3C/I2C frames must be called in
non-atomic context. Mainly done this way to ease implementation, but
this is not set in stone, and if anyone needs async support, new
functions can be added later on.
- the bus element is a separate object, but it's tightly coupled with
the master object. We thus have a 1:1 relationship between i3c_bus
and i3c_master_controller objects, and if 2 master controllers are
connected to the same bus and both exposed to the same Linux instance
they will appear as two distinct busses, and devices on this bus will
be exposed twice.
- I2C backward compatibility has been designed to be transparent to I2C
drivers and the I2C subsystem. The I3C master just registers an I2C
adapter which creates a new I2C bus. I'd say that, from a
representation PoV it's not ideal because what should appear as a
single I3C bus exposing I3C and I2C devices here appears as 2
different buses connected to each other through the parenting (the
I3C master is the parent of the I2C and I3C busses).
On the other hand, I don't see a better solution if we want something
that is not invasive.

Missing features:
- I3C HDR modes are not supported
- no support for multi-master and the associated concepts (mastership
handover, support for secondary masters, ...)
- I2C devices can only be described using DT because this is the only
use case I have. However, the framework can easily be extended with
ACPI and board info support
- I3C slave framework. This has been completely omitted, but shouldn't
have a huge impact on the I3C framework because I3C slaves don't see
the whole bus, it's only about handling master requests and generating
IBIs. Some of the struct, constant and enum definitions could be
shared, but most of the I3C slave framework logic will be different

Signed-off-by: Boris Brezillon <boris.brezillon@bootlin.com>
Reviewed-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>