> Very good idea to use a slave to send the Host-Notify command to the host
> for testing. Later on, for SMBus-Alert, a GPIO can be used to loop it back
> to the tested master to verify that SMBus-Alert is working fine.

Glad you like it! Yes, SMBusAlert is the next addition planned.

> What you implemented is the "remote" side which I understood is meant to
> replace a "real" device for those features which are not that common.

Correct.

> Shouldn't we also have the "master" side loopback test driver as well to
> work with this test slave driver ?

Yes, ultimately we want that. But for this first draft, I simply
triggered with 'i2cset' and checked debug prints plus debugfs for
desired outcome.

> For example for the Host-Notify that master side loopback test driver would
> perform the request_irq allowing it to be called back when the slave test
> driver sends the host-notify command.
> In case of SMBus-Alert, that would be implementing the .alert function that
> would be called when the SMBus-Alert is received ..

Exactly. I am simply focussed on the remote side for now because I am
curious if it works at all. And what other parts need fixing, e.g. the
I2C core patch I sent a few minutes ago.

> With that the whole loop can be automatically tested. This kind of stuff
> can of course be enhanced to a LOT of cases .... basically something similar
> to spi-loopback driver for example except that in case of i2c it needs 2
> I2C controllers instead of one for the SPI.

This is my ultimate goal, too: scriptable tests for I2C mastes. Basic
functionality can be tested with a simple device, say an EEPROM. But the
rare stuff needs something like this testunit.