netdev - RE: [PATCH v1 net-next] net: dsa: Allow only up to two HSR HW offloaded ports for KSZ9477

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Message-ID: <BL0PR11MB291397353642C808454F575CE7CE2@BL0PR11MB2913.namprd11.prod.outlook.com>
Date: Tue, 18 Jun 2024 14:31:28 +0000
From: <Woojung.Huh@...rochip.com>
To: <dan.carpenter@...aro.org>, <andrew@...n.ch>
CC: <lukma@...x.de>, <olteanv@...il.com>, <kuba@...nel.org>,
	<netdev@...r.kernel.org>, <pabeni@...hat.com>, <edumazet@...gle.com>,
	<davem@...emloft.net>, <o.rempel@...gutronix.de>,
	<Tristram.Ha@...rochip.com>, <bigeasy@...utronix.de>, <horms@...nel.org>,
	<ricardo@...liere.net>, <casper.casan@...il.com>,
	<linux-kernel@...r.kernel.org>, <UNGLinuxDriver@...rochip.com>
Subject: RE: [PATCH v1 net-next] net: dsa: Allow only up to two HSR HW
 offloaded ports for KSZ9477

Hi Dan & Andrew,

> On Tue, Jun 18, 2024 at 03:52:23PM +0200, Andrew Lunn wrote:
> > > diff --git a/drivers/net/dsa/microchip/ksz_common.c
> b/drivers/net/dsa/microchip/ksz_common.c
> > > index 2818e24e2a51..181e81af3a78 100644
> > > --- a/drivers/net/dsa/microchip/ksz_common.c
> > > +++ b/drivers/net/dsa/microchip/ksz_common.c
> > > @@ -3906,6 +3906,11 @@ static int ksz_hsr_join(struct dsa_switch *ds,
> int port, struct net_device *hsr,
> > >             return -EOPNOTSUPP;
> > >     }
> > >
> > > +   if (hweight8(dev->hsr_ports) > 1) {
> > > +           NL_SET_ERR_MSG_MOD(extack, "Cannot offload more than two
> ports (in use=0x%x)", dev->hsr_ports);
> > > +           return -EOPNOTSUPP;
> > > +   }
> >
> > Hi Dan
> >
> > I don't know HSR to well, but this is offloading to hardware, to
> > accelerate what Linux is already doing in software. It should be, if
> > the hardware says it cannot do it, software will continue to do the
> > job. So the extack message should never be seen.
> 
> Ah.  Okay.  However the rest of the function prints similar messages
> and so probably we could remove those error messages as well.  To be
> honest, I just wanted something which functioned as a comment and
> mentioned "two ports".  Perhaps the condition would be more clear as
> >= 2 instead of > 1?
> 

I'm not a HSR expert and so could be a dummy question.

I think this case (upto 2 HSR port offload) is different from other offload error.
Others are checking whether offload is possible or not, so SW HSR can kick in
when -EOPNOTSUPP returns. However, this happens when joining 3rd (2+) port
with hardware offload is enabled.
It is still working two ports are in HW HSR offload and next ports are in SW HSR?

Thanks.
Woojung