Re: fwnode_for_each_child_node() and OF backend discrepancy

[Michael Walle]

[adding Horatiu Vultur, because we now digress to the bug
in the switch, rather than that odd OF behavior]

Am 2022-06-28 15:29, schrieb Andy Shevchenko:
> On Tue, Jun 28, 2022 at 3:23 PM Michael Walle <michael@xxxxxxxx> wrote:
> > >> I was trying to fix the lan966x driver [1] which doesn't work if there
> > >> are disabled nodes in between.
> > >
> > > Can you elaborate what's wrong now in the behaviour of the driver? In
> > > the code it uses twice the _available variant.
> >
> > Imagine the following device tree snippet:
> >   port0 {
> >     reg = <0>;
> >     status = "okay";
> >   }
> >   port1 {
> >     reg = <1>;
> >     status = "disabled";
> >   }
> >   port@2 {
> >     reg = <2>;
> >     status = "okay";
> >   }
> >
> > The driver will set num_phys_ports to 2. When port@2 is probed, it
> > will have the (correct!) physical port number 2. That will then
> > trigger various EINVAL checks with "port_num >= num_phys_ports" or
> > WARN()s.
>
> It means the above mentioned condition is wrong: it should be
>
> "port_idx >= num_phys_ports" (if the port_idx doesn't exists, that's
> the bug in the first place)

I can't follow you here. Please note, that you need the actual
physical port number. It's not a made up number, but corresponds
to a physical port on that ethernet switch. So you can't just skip
the disabled ones. port@2 must have port number 2.

> > So the easiest fix would be to actual count all the child nodes
> > (regardless if they are available or not), assuming there are as
> > many nodes as physical ports.
> >
> > But num_phys_ports being a property of the hardware
>
> So, name is wrong, that's how I read it, it should be
> num_of_acrive_phys_ports (or alike).

See above, it is not just an iterator but corresponds to
a hardware property.

> > I don't
> > think it's good to deduce it by counting the child nodes anyway,
>
> Right.
>
> > but it should rather be a (hardcoded) property of the driver.
>
> Also good to update.

Horatiu, can we determine the actual number of ports (or maybe
determine if its a LAN9668 or a LAN9662) from the hardware itself
in an easy way? That way we wouldn't need a new compatible string,
but could use the generic "lan966x" one.

-michael

[1] 
https://elixir.bootlin.com/linux/v5.19-rc4/source/drivers/net/ethernet/microchip/lan966x/lan966x_main.c