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>

1 files changed, 17 insertions, 0 deletions

diff --git a/include/linux/mod_devicetable.h b/include/linux/mod_devicetable.h
index 01797cb4587e..cbd94df31743 100644
--- a/include/linux/mod_devicetable.h
+++ b/include/linux/mod_devicetable.h
@@ -448,6 +448,23 @@ struct pci_epf_device_id {
 	kernel_ulong_t driver_data;
 };
 
+/* i3c */
+
+#define I3C_MATCH_DCR			0x1
+#define I3C_MATCH_MANUF			0x2
+#define I3C_MATCH_PART			0x4
+#define I3C_MATCH_EXTRA_INFO		0x8
+
+struct i3c_device_id {
+	__u8 match_flags;
+	__u8 dcr;
+	__u16 manuf_id;
+	__u16 part_id;
+	__u16 extra_info;
+
+	const void *data;
+};
+
 /* spi */
 
 #define SPI_NAME_SIZE	32