netdev - Re: Choose a default DSA CPU port

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Date:   Tue, 28 Feb 2023 14:48:13 +0100
From:   Frank Wunderlich <frank-w@...lic-files.de>
To:     Vladimir Oltean <olteanv@...il.com>
CC:     Arınç ÜNAL <arinc.unal@...nc9.com>,
        Felix Fietkau <nbd@....name>, netdev <netdev@...r.kernel.org>,
        erkin.bozoglu@...ont.com, Andrew Lunn <andrew@...n.ch>,
        Florian Fainelli <f.fainelli@...il.com>,
        John Crispin <john@...ozen.org>,
        Mark Lee <Mark-MC.Lee@...iatek.com>,
        Lorenzo Bianconi <lorenzo@...nel.org>,
        Matthias Brugger <matthias.bgg@...il.com>,
        Landen Chao <Landen.Chao@...iatek.com>,
        Sean Wang <sean.wang@...iatek.com>,
        DENG Qingfang <dqfext@...il.com>
Subject: Re: Choose a default DSA CPU port

Am 28. Februar 2023 12:58:46 MEZ schrieb Vladimir Oltean <olteanv@...il.com>:
>On Sun, Feb 26, 2023 at 01:12:04PM +0100, Frank Wunderlich wrote:
>> but back to topic...we have a patch from vladuimir which allows
>> setting the preferred cpu-port...how do we handle mt7531 here
>> correctly (which still sets port5 if defined and then break)?
>> 
>> https://git.kernel.org/pub/scm/linux/kernel/git/netdev/net-next.git/tree/drivers/net/dsa/mt7530.c#n2383
>> 
>> 	/* BPDU to CPU port */
>> 	dsa_switch_for_each_cpu_port(cpu_dp, ds) {
>> 		mt7530_rmw(priv, MT7531_CFC, MT7531_CPU_PMAP_MASK,
>> 			   BIT(cpu_dp->index));
>> 		break; //<<< should we drop this break only to set all "cpu-bits"? what happens then (flooding both ports with packets?)
>> 	}
>> 
>> as dsa only handles only 1 cpu-port we want the real cpu-port
>> (preferred | first). is this bit set also if the master is changed
>> with your follow-up patch?
>
>Could you please make a best-effort attempt at describing what does the
>MT7531_CFC[MT7531_CPU_PMAP_MASK] register affect? From the comment, if
>affects the trapping of control packets. Does the MT7530 not have this
>register? Do they behave differently? Does the register affect anything
>else? If that logic is commented out, does DSA-tagged traffic still work
>on MT7531? How about a bridge created with stp_state 1? I don't
>understand at the moment why the hardware allows specifying a port mask
>rather than a single port. Intuitively I'd say that if this field
>contains more than one bit set, then control packets would be delivered
>to all CPU ports that are up, effectively resulting in double processing
>in Linux. So that doesn't seem to be useful. But I don't have enough data.

I have only this datasheet from bpi for mt7531

https://drive.google.com/file/d/1aVdQz3rbKWjkvdga8-LQ-VFXjmHR8yf9/view

On page 23 the register is defined but without additional information about setting multiple bits in this range. CFC IS CPU_FORWARD_CONTROL register and CPU_PMAP is a 8bit part of it which have a bit for selecting each port as cpu-port (0-7). I found no information about packets sent over both cpu-ports, round-robin or something else.

For mt7530 i have no such document.

The way i got from mtk some time ago was using a vlan_aware bridge for selecting a "cpu-port" for a specific user-port. At this point port5 was no cpu-port and traffic is directly routed to this port bypassing dsa and the cpu-port define in driver...afaik this way port5 was handled as userport too.
regards Frank