[RFC PATCH 0/4] hw/i2c: i2c slave mode support

[Klaus Jensen <its@irrelevant.dk>]

From: Klaus Jensen <k.jensen@samsung.com>

Hi all,

This RFC series adds I2C "slave mode" support for the Aspeed I2C
controller as well as the necessary infrastructure in the i2c core to
support this.

Background
~~~~~~~~~~
We are working on an emulated NVM Express Management Interface[1] for
testing and validation purposes. NVMe-MI is based on the MCTP
protocol[2] which may use a variety of underlying transports. The one we
are interested in is I2C[3].

The first general trickery here is that all MCTP transactions are based
on the SMBus Block Write bus protocol[4]. This means that the slave must
be able to master the bus to communicate. As you know, hw/i2c/core.c
currently does not support this use case.

The second issue is how to interact with these mastering devices. Jeremy
and Matt (CC'ed) have been working on an MCTP stack for the Linux Kernel
(already upstream) and an I2C binding driver[5] is currently under
review. This binding driver relies on I2C slave mode support in the I2C
controller.

This series
~~~~~~~~~~~
Patch 1 adds support for multiple masters in the i2c core, allowing
slaves to master the bus and safely issue i2c_send/recv(). Patch 2 adds
an asynchronous send i2c_send_async(I2CBus *, uint8) on the bus that
must be paired with an explicit ack using i2c_ack(I2CBus *).

Patch 3 adds the slave mode functionality to the emulated Aspeed I2C
controller. The implementation is probably buggy since I had to rely on
the implementation of the kernel driver to reverse engineer the behavior
of the controller slave mode (I do not have access to a spec sheet for
the Aspeed, but maybe someone can help me out with that?).

Finally, patch 4 adds an example device using this new API. The device
is a simple "echo" device that upon being sent a set of bytes uses the
first byte as the address of the slave to echo to.

With this combined I am able to boot up Linux on an emulated Aspeed 2600
evaluation board and have the i2c echo device write into a Linux slave
EEPROM. Assuming the echo device is on address 0x42:

  # echo slave-24c02 0x1064 > /sys/bus/i2c/devices/i2c-15/new_device
  i2c i2c-15: new_device: Instantiated device slave-24c02 at 0x64
  # i2cset -y 15 0x42 0x64 0x00 0xaa i
  # hexdump /sys/bus/i2c/devices/15-1064/slave-eeprom
  0000000 ffaa ffff ffff ffff ffff ffff ffff ffff
  0000010 ffff ffff ffff ffff ffff ffff ffff ffff
  *
  0000100

  [1]: https://nvmexpress.org/developers/nvme-mi-specification/
  [2]: https://www.dmtf.org/sites/default/files/standards/documents/DSP0236_1.3.1.pdf
  [3]: https://www.dmtf.org/sites/default/files/standards/documents/DSP0237_1.2.0.pdf
  [4]: http://www.smbus.org/specs/SMBus_3_1_20180319.pdf
  [5]: https://lore.kernel.org/linux-i2c/20220218055106.1944485-1-matt@codeconstruct.com.au/

Klaus Jensen (4):
  hw/i2c: support multiple masters
  hw/i2c: add async send
  hw/i2c: add slave mode for aspeed_i2c
  hw/misc: add a toy i2c echo device

 hw/i2c/aspeed_i2c.c         |  95 +++++++++++++++++++++---
 hw/i2c/core.c               |  57 +++++++++++++-
 hw/i2c/trace-events         |   2 +-
 hw/misc/i2c-echo.c          | 144 ++++++++++++++++++++++++++++++++++++
 hw/misc/meson.build         |   2 +
 include/hw/i2c/aspeed_i2c.h |   8 ++
 include/hw/i2c/i2c.h        |  19 +++++
 7 files changed, 316 insertions(+), 11 deletions(-)
 create mode 100644 hw/misc/i2c-echo.c

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2.35.1