Re: [PATCH net v2 2/2] net: dsa: b53: restore the NSP IMP port 2 Gbps mode

[Florian Fainelli]

On 10/26/26 11:31, Jonas Gorski wrote:
> Hi,
>
> On Thu, Oct 22, 2026 at 11:11 PM Florian Fainelli
> <florian.fainelli@xxxxxxxxxxxx> wrote:
> > The Northstar Plus IMP port uses the switch's proprietary 2 Gbps mode for
> > its internal link to the AMAC.  Its fixed-link description reports 1 Gbps,
> > so applying that speed clears PORT_OVERRIDE_SPEED_2000M and leaves the two
> > ends of the internal link configured at different speeds.
>
> Sounds like the devicetrees are wrong. Shouldn't that fixed-link
> description be updated to be 2 Gbps then? ;p

That's a fair ask, however that would require introducing 2Gbits/sec all 
over the place, and it's not like we really have a good way to report 
that even through emulated PHY registers. This would not be a bug fix 
however, which this patch set is targeting.

> > Force the 2 Gbps mode and flow control for BCM5301x and NSP CPU ports.  The
> > mismatch caused switch output queue discards on both copper and SerDes
> > ports, with one discard for every TCP retransmission.  With both ends
> > restored to their high-speed modes, iperf3 reports no retransmissions.
> >
> > Fixes: b6a8a5477fe9 ("net: dsa: b53: fix resetting speed and pause on forced link")
> > Signed-off-by: Florian Fainelli <florian.fainelli@xxxxxxxxxxxx>
> > ---
> >   drivers/net/dsa/b53/b53_common.c | 10 +++++++---
> >   1 file changed, 7 insertions(+), 3 deletions(-)
> >
> > diff --git a/drivers/net/dsa/b53/b53_common.c b/drivers/net/dsa/b53/b53_common.c
> > index 0880310c9ce3..1f4964c28fc5 100644
> > --- a/drivers/net/dsa/b53/b53_common.c
> > +++ b/drivers/net/dsa/b53/b53_common.c
> > @@ -1663,9 +1663,13 @@ static void b53_phylink_mac_link_up(struct phylink_config *config,
> >          }
> >
> >          if (mode == MLO_AN_FIXED) {
> > -               /* Force flow control on BCM5301x's CPU port */
> > -               if (is5301x(dev) && dsa_is_cpu_port(ds, port))
> > -                       tx_pause = rx_pause = true;
> > +               /* Force flow control on BCM5301x and NSP CPU ports */
>
> The comment is now outdated, and is missing the forced 2G mode.

Ack.
--
Florian