Re: [PATCH devicetree 0/3] NXP LS1028A DT changes for multiple switch CPU ports

[Michael Walle]

Am 2022-08-18 16:55, schrieb Vladimir Oltean:
> On Thu, Aug 18, 2022 at 04:49:49PM +0200, Michael Walle wrote:
> > Is it used automatically or does the userspace has to configure 
> > something?
>
> DSA doesn't yet support multiple CPU ports, but even when it will, the
> second DSA master still won't be used automatically. If you want more
> details about the proposed UAPI to use the second CPU port, see here:
> https://patchwork.kernel.org/project/netdevbpf/cover/20220523104256.3556016-1-olteanv@xxxxxxxxx/
>
> > > Care has been taken that this change does not produce regressions when
> > > using updated device trees with old kernels that do not support multiple
> > > DSA CPU ports. The only difference for old kernels will be the
> > > appearance of a new net device (for &enetc_port3) which will not be very
> > > useful for much of anything.
> >
> > Mh, I don't understand. Does it now cause regressions or not? I mean
> > besides that there is a new unused interface?
>
> It didn't cause regressions until kernel 5.13 when commit adb3dccf090b
> ("net: dsa: felix: convert to the new .change_tag_protocol DSA API")
> happened, then commit 00fa91bc9cc2 ("net: dsa: felix: fix tagging
> protocol changes with multiple CPU ports") fixed that regression and 
> was
> backported to the linux-5.15.y stable branch AFAIR. So at least kernels
> 5.15 and newer should work properly with the new device trees.

Thanks for the details!

> > I was just thinking of that systemready stuff where the u-boot might
> > supply its (newer) device tree to an older kernel, i.e. an older 
> > debian
> > or similar.
> >
> > -michael
>
> Yeah, I hear you, I'm doing my best to make the driver work with a
> one-size-fits-all device tree, both ways around.

TBH I don't really care much, I was merely curious what to expect.

-michael