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Message-ID: <CA+h21hp8LueSfh+Z8f0-Y7dTPB50d+3E3K9n6R5MwNzA3Dh1Lw@mail.gmail.com>
Date: Fri, 10 Apr 2020 13:46:45 +0300
From: Vladimir Oltean <olteanv@...il.com>
To: DENG Qingfang <dqfext@...il.com>
Cc: Florian Fainelli <f.fainelli@...il.com>,
David Miller <davem@...emloft.net>,
netdev <netdev@...r.kernel.org>,
René van Dorst <opensource@...rst.com>,
John Crispin <john@...ozen.org>,
Vivien Didelot <vivien.didelot@...il.com>,
Andrew Lunn <andrew@...n.ch>,
Sean Wang <sean.wang@...iatek.com>,
Weijie Gao <weijie.gao@...iatek.com>,
"moderated list:ARM/Mediatek SoC support"
<linux-mediatek@...ts.infradead.org>
Subject: Re: [PATCH net-next] net: dsa: mt7530: enable jumbo frame
Hi Qingfang,
On Fri, 10 Apr 2020 at 05:51, DENG Qingfang <dqfext@...il.com> wrote:
>
> On Fri, Apr 10, 2020 at 10:27 AM Florian Fainelli <f.fainelli@...il.com> wrote:
> >
> >
> >
> > On 4/9/2020 7:19 PM, DENG Qingfang wrote:
> > > So, since nothing else uses the mt7530_set_jumbo function, should I
> > > remove the function and just add a single rmw to mt7530_setup?
> >
> > (please do not top-post on netdev)
> >
> > There is a proper way to support the MTU configuration for DSA switch
> > drivers which is:
> >
> > /*
> > * MTU change functionality. Switches can also adjust their MRU
> > through
> > * this method. By MTU, one understands the SDU (L2 payload) length.
> > * If the switch needs to account for the DSA tag on the CPU
> > port, this
> > * method needs to to do so privately.
> > */
> > int (*port_change_mtu)(struct dsa_switch *ds, int port,
> > int new_mtu);
> > int (*port_max_mtu)(struct dsa_switch *ds, int port);
>
> MT7530 does not support configuring jumbo frame per-port
> The register affects globally
>
> >
> > --
> > Florian
This is a bit more tricky, but I think you can still deal with it
using the port_change_mtu functionality. Basically it is only a
problem when the other ports are standalone - otherwise the
dsa_bridge_mtu_normalization function should kick in.
So if you implement port_change_mtu, you should do something along the lines of:
for (i = 0; i < MT7530_NUM_PORTS; i++) {
struct net_device *slave;
if (!dsa_is_user_port(ds, i))
continue;
slave = ds->ports[i].slave;
slave->mtu = new_mtu;
}
to update the MTU known by the stack for all net devices.
Hope this helps,
-Vladimir
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