This patch series is a proposal for a new I3C subsystem.
This infrastructure is not complete yet and will be extended over
time.
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 still open to discussion. Please let me know if you think it's
worth considering an asynchronous model here
- the bus element is a separate object and is not implicitly described
by the master (as done in I2C). The reason is that I want to be able
to handle multiple master connected to the same bus and visible to
Linux.
In this situation, we should only have one instance of the device and
not one per master, and sharing the bus object would be part of the
solution to gracefully handle this case.
I'm not sure if we will ever need to deal with multiple masters
controlling the same bus and exposed under Linux, but separating the
bus and master concept is pretty easy, hence the decision to do it
now, just in case we need it some day.
The other benefit of separating the bus and master concepts is that
master devices appear under the bus directory in sysfs.
Discussion around the bus/master/dev representation is still ongoing,
with Arnd opting for a simple approach where
* the bus is implicitly represented by the master device
* the master is not represented as a device under the I3C bus
* only remote I3C devices are exposed and possibly duplicated if
several masters controlling the same bus are exposed to the same
Linux instance
and Peter preferring the representation where the bus is a separate
object. IIRC, Wolfram was in favor of the "bus is a separate object"
too.
If possible, I'd like to close this discussion soon, no matter which
solution is chosen.
- 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 busses 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 in this preliminary version:
- support for HDR modes (has been removed because of lack of real users)
- 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
Main changes between v5 and v6:
- Introduce {i3c,i2c}_dev_desc structures to better match how I3C
master controllers (reservation of one HW slot for each device
attached to the bus). With this solution, the resource migration
that happens when a device lose its dynamic address and is
re-assigned a different address is simplified on the driver side,
because most of it is now handled in the core (reserve a new dev
slot, reserve IBI resources and free all resources attached to the
old slot)
- Add I3C error codes (M0 to M2) so that the core and device drivers
can have fine grained information on what caused an EIO error.
Only minor things happened between v3 and v5 (you can go check the
changelog in each patch for more details).
Main changes between v2 and v3 are:
- Reworked the DT bindings as suggested by Rob
- Reworked the bus initialization step as suggested by Vitor
- Added a driver for an I3C GPIO expander
Main changes between the initial RFC and this v2 are:
- Add a generic infrastructure to support IBIs. It's worth mentioning
that I tried exposing IBIs as a regular IRQs, but after several
attempts and a discussion with Mark Zyngier, it appeared that it was
not really fitting in the Linux IRQ model (the fact that you have
payload attached to IBIs, the fact that most of the time an IBI will
generate a transfer on the bus which has to be done in an atomic
context, ...)
The counterpart of this decision is the latency induced by the
workqueue approach, but since I don't have real use cases, I don't
know if this can be a problem or not.
- Add helpers to support Hot Join
- Add support for IBIs and Hot Join in Cadence I3C master driver
- Address several issues in how I was using the device model
Thanks,
Boris
Boris Brezillon (10):
i3c: Add core I3C infrastructure
docs: driver-api: Add I3C documentation
i3c: Add sysfs ABI spec
dt-bindings: i3c: Document core bindings
dt-bindings: i3c: Add macros to help fill I3C/I2C device's reg
property
MAINTAINERS: Add myself as the I3C subsystem maintainer
i3c: master: Add driver for Cadence IP
dt-bindings: i3c: Document Cadence I3C master bindings
gpio: Add a driver for Cadence I3C GPIO expander
dt-bindings: gpio: Add bindings for Cadence I3C gpio expander
Documentation/ABI/testing/sysfs-bus-i3c | 95 +
.../devicetree/bindings/gpio/gpio-cdns-i3c.txt | 39 +
.../devicetree/bindings/i3c/cdns,i3c-master.txt | 44 +
Documentation/devicetree/bindings/i3c/i3c.txt | 140 ++
Documentation/driver-api/i3c/device-driver-api.rst | 9 +
Documentation/driver-api/i3c/index.rst | 11 +
Documentation/driver-api/i3c/master-driver-api.rst | 10 +
Documentation/driver-api/i3c/protocol.rst | 203 ++
Documentation/driver-api/index.rst | 1 +
MAINTAINERS | 10 +
drivers/Kconfig | 2 +
drivers/Makefile | 2 +-
drivers/gpio/Kconfig | 11 +
drivers/gpio/Makefile | 1 +
drivers/gpio/gpio-cdns-i3c.c | 411 ++++
drivers/i3c/Kconfig | 24 +
drivers/i3c/Makefile | 4 +
drivers/i3c/core.c | 606 ++++++
drivers/i3c/device.c | 233 +++
drivers/i3c/internals.h | 36 +
drivers/i3c/master.c | 2058 ++++++++++++++++++++
drivers/i3c/master/Kconfig | 5 +
drivers/i3c/master/Makefile | 1 +
drivers/i3c/master/i3c-master-cdns.c | 1668 ++++++++++++++++
include/dt-bindings/i3c/i3c.h | 28 +
include/linux/i3c/ccc.h | 385 ++++
include/linux/i3c/device.h | 331 ++++
include/linux/i3c/master.h | 652 +++++++
include/linux/mod_devicetable.h | 17 +
29 files changed, 7036 insertions(+), 1 deletion(-)
create mode 100644 Documentation/ABI/testing/sysfs-bus-i3c
create mode 100644 Documentation/devicetree/bindings/gpio/gpio-cdns-i3c.txt
create mode 100644 Documentation/devicetree/bindings/i3c/cdns,i3c-master.txt
create mode 100644 Documentation/devicetree/bindings/i3c/i3c.txt
create mode 100644 Documentation/driver-api/i3c/device-driver-api.rst
create mode 100644 Documentation/driver-api/i3c/index.rst
create mode 100644 Documentation/driver-api/i3c/master-driver-api.rst
create mode 100644 Documentation/driver-api/i3c/protocol.rst
create mode 100644 drivers/gpio/gpio-cdns-i3c.c
create mode 100644 drivers/i3c/Kconfig
create mode 100644 drivers/i3c/Makefile
create mode 100644 drivers/i3c/core.c
create mode 100644 drivers/i3c/device.c
create mode 100644 drivers/i3c/internals.h
create mode 100644 drivers/i3c/master.c
create mode 100644 drivers/i3c/master/Kconfig
create mode 100644 drivers/i3c/master/Makefile
create mode 100644 drivers/i3c/master/i3c-master-cdns.c
create mode 100644 include/dt-bindings/i3c/i3c.h
create mode 100644 include/linux/i3c/ccc.h
create mode 100644 include/linux/i3c/device.h
create mode 100644 include/linux/i3c/master.h
--
2.14.1
