On Tue, Oct 5, 2021 at 6:28 PM Alexandre Belloni
[off-list ref] wrote:

On 05/10/2021 18:22:12+0200, Arnd Bergmann wrote:

quoted

On Tue, Oct 5, 2021 at 4:37 PM Paweł Anikiel [off-list ref] wrote:

quoted

On SoCFPGA systems, it's desireable to have fixed numbering for
i2c busses, while being able to enable/disable them (e.g. have i2c1
be mapped to /dev/i2c-1, even though i2c0 is disabled). This can also
be achieved using devicetree aliases (see i2c_add_adapter). However,
having the driver be self-contained without relying on aliases is more
robust.

Signed-off-by: Paweł Anikiel <redacted>

I don't see how adding a nonstandard property in one of the i2c bus
drivers helps at all. How do you expect this to work when there are
multiple i2c controllers in the system using different drivers? What
should happen if both an alias and the busno property are set?

What happens when two nodes have the same busno property because e.g.
one is in a dtsi and the other one is in a dts?

If busno is set, the alias is ignored (the code that checks aliases
is never reached). If two nodes have the same busno property, we get
a WARN in drivers/i2c/i2c-core-base.c:1637, and only on of them
gets attached.

What is a better way of doing this then? Is adding aliases to the
devicetree like this okay?

aliases {
...
i2c0 = &i2c0;
i2c1 = &i2c1;
};