Re: [PATCH RFC 0/1] i2c: add slave testunit driver

[Alain Volmat <alain.volmat@st.com>]

Hi Wolfram,

On Mon, Jun 29, 2020 at 06:53:17PM +0000, Wolfram Sang wrote:
> Motivated by a series by Alain Volmat which implements SMBus Host Notify
> support as a slave backend[1], I wondered how I could actually test it.
> Then, I picked up my old idea of a "custom remote device" and
> implemented it as another slave backend. This is the first draft and it
> works quite well on my Renesas Lager board where I connected two I2C
> busses where both I2C controllers are master and slave. One slave is the
> testunit, one slave is the HostNotify listener.
> 
> While I really like Alain's approach, there is still some more testing
> needed. So, I already release my testing environment, maybe other people
> are interested, too. This patch depends on a documentation update. Also,
> for Renesas R-Car SoCs, some fixes are needed. I suggest you simply pull
> this branch here:
> 
> git://git.kernel.org/pub/scm/linux/kernel/git/wsa/linux.git renesas/i2c/slave-testunit
> 
> As mentioned elsewhere, support for SMBus Alert and I2C_M_RECV_LEN are
> already planned. But I guess you can do much more.
> 
> Ideas and comments welcome!

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.

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

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.

> 
> Happy hacking,
> 
>    Wolfram
> 
> [1] http://patchwork.ozlabs.org/project/linux-i2c/list/?series=185718&state=*
> 
> Wolfram Sang (1):
>   i2c: add slave testunit driver
> 
>  Documentation/i2c/slave-testunit-backend.rst |  48 ++++++
>  drivers/i2c/Kconfig                          |   8 +
>  drivers/i2c/Makefile                         |   1 +
>  drivers/i2c/i2c-slave-testunit.c             | 146 +++++++++++++++++++
>  4 files changed, 203 insertions(+)
>  create mode 100644 Documentation/i2c/slave-testunit-backend.rst
>  create mode 100644 drivers/i2c/i2c-slave-testunit.c
> 
> -- 
> 2.20.1
>