Re: [patch net-next RFC 00/10] introduce line card support for modular switch

Wed, Jan 27, 2021 at 03:14:34PM CET, andrew@lunn.ch wrote:

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There are Linux standard APIs for controlling the power to devices,
the regulator API. So i assume mlxreg-pm will make use of that. There
are also standard APIs for thermal management, which again, mlxreg-pm
should be using. The regulator API allows you to find regulators by
name. So just define a sensible naming convention, and the switch
driver can lookup the regulator, and turn it on/off as needed.

I don't think it would apply. The thing is, i2c driver has a channel to
the linecard eeprom, from where it can read info about the linecard. The
i2c driver also knows when the linecard is plugged in, unlike mlxsw.
It acts as a standalone driver. Mlxsw has no way to directly find if the
card was plugged in (unpowered) and which type it is.

Not sure how to "embed" it. I don't think any existing API could help.
Basicall mlxsw would have to register a callback to the i2c driver
called every time card is inserted to do auto-provision.
Now consider a case when there are multiple instances of the ASIC on the
system. How to assemble a relationship between mlxsw instance and i2c
driver instance?

You have that knowledge already, otherwise you cannot solve this

No I don't have it. I'm not sure why do you say so. The mlxsw and i2c
driver act independently.

problem at all. The switch is an PCIe device right? So when the bus is
enumerated, the driver loads. How do you bind the i2c driver to the
i2c bus? You cannot enumerate i2c, so you must have some hard coded
knowledge somewhere? You just need to get that knowledge into the
mlxsw driver so it can bind its internal i2c client driver to the i2c

There is no internal i2c client driver for this.

bus. That way you avoid user space, i guess maybe udev rules, or some
daemon monitoring propriety /sys files?

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But again, auto-provision is only one usecase. Manual provisioning is
needed anyway. And that is exactly what my patchset is aiming to
introduce. Auto-provision can be added when/if needed later on.

I still don't actually get this use case. Why would i want to manually
provision?

Because user might want to see the system with all netdevices, configure
them, change the linecard if they got broken and all config, like
bridge, tc, etc will stay on the netdevices. Again, this is the same we
do for split port. This is important requirement, user don't want to see
netdevices come and go when he is plugging/unplugging cables. Linecards
are the same in this matter. Basically is is a "splitter module",
replacing the "splitter cable"

Andrew