[RFC PATCH v2 0/6] 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.

v2 changes
~~~~~~~~~~
I finally got around to working on this again. I'm sorry for not
bringing a v2 to the table earlier.

Mad props to Peter and Jonathan for putting this series to work and
pushing it forward! Thanks!

This series is based off Cédric's aspeed-7.1 tree, so it includes the
register fields. This is all "old register mode", but Peter seems to
have added support in new mode.

There are some loose ends of course, i.e send_async doesn't handle
broadcast and asynchronous slaves being sent stuff can't nack. But I
wanted to get some feedback on the interface before I tackle that.

This series
~~~~~~~~~~~
Patch 1 and 2 are small Aspeed I2C changes/additions.

Patch 3 adds support for multiple masters in the i2c core, allowing
slaves to master the bus and (safely) issue i2c_send/recv().

Patch 4 adds an asynchronous send i2c_send_async(I2CBus *, uint8) on the
bus that must be paired with an explicit ack using i2c_ack(I2CBus *). We
have previously discussed how we wanted to handle the issue that some
slaves implement this and some do not. Using a QOM interface was up, but
couldn't figure out a good way to do it. I ended up decided against it
since I believe this have to be a run-time check anyway. The problem is
that a slave can master the bus and try to communicate with *anyone* on
the bus - and there is no reason why we should only allow asynchronous
slaves on the bus in that case, or whatever we would want to do when
devices are plugged. So, instead, the current master can issue an
i2c_start_send() and if that fails (because it isnt implemented by the
target slave) it can either bail out or use i2c_start_send_async() if it
itself supports it. This works the other way around as well of course,
but it is probably simpler to handle slaves that respond to
i2c_start_send(). This approach relies on adding a new i2c_event, which
is why a bunch of other devices needs changes in their event handling.

Patch 5 adds *partial* slave mode functionality to the emulated Aspeed
I2C controller, that is, it only supports asynchronous sends started by
another slave that is currently mastering the bus. No asynchronous
receive.

Finally, patch 6 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

Klaus Jensen (6):
  hw/i2c/aspeed: rework raise interrupt trace event
  hw/i2c/aspeed: add DEV_ADDR in old register mode
  hw/i2c: support multiple masters
  hw/i2c: add asynchronous send
  hw/i2c/aspeed: add slave device in old register mode
  hw/misc: add a toy i2c echo device [DO NOT PULL]

 hw/arm/pxa2xx.c             |   2 +
 hw/display/sii9022.c        |   2 +
 hw/display/ssd0303.c        |   2 +
 hw/i2c/aspeed_i2c.c         | 152 ++++++++++++++++++++++++++++-----
 hw/i2c/core.c               |  70 +++++++++++++++-
 hw/i2c/smbus_slave.c        |   4 +
 hw/i2c/trace-events         |   4 +-
 hw/misc/i2c-echo.c          | 162 ++++++++++++++++++++++++++++++++++++
 hw/misc/ibm-cffps.c         |   2 +
 hw/misc/ir35221.c           |   2 +
 hw/misc/meson.build         |   2 +
 hw/nvram/eeprom_at24c.c     |   2 +
 hw/sensor/lsm303dlhc_mag.c  |   2 +
 include/hw/i2c/aspeed_i2c.h |  16 ++++
 include/hw/i2c/i2c.h        |  30 +++++++
 15 files changed, 428 insertions(+), 26 deletions(-)
 create mode 100644 hw/misc/i2c-echo.c

-- 
2.36.1