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

[Florian Fainelli <florian.fainelli@broadcom.com>]

On 10/26/26 11:31, Jonas Gorski wrote:
> Hi,
> 
> On Thu, Oct 22, 2026 at 11:11 PM Florian Fainelli
> <florian.fainelli@broadcom.com> 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@broadcom.com>
>> ---
>>   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 The comment is now outdated, and is missing the forced 2G mode.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