netdev - Re: [PATCH net-next 15/15] net: mscc: ocelot: don't hardcode the number of the CPU port

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Message-ID: <d99479d0-b5c2-bee2-73ff-7d9235840225@gmail.com>
Date:   Sun, 10 Nov 2019 12:54:19 -0800
From:   Florian Fainelli <f.fainelli@...il.com>
To:     Vladimir Oltean <olteanv@...il.com>, Andrew Lunn <andrew@...n.ch>
Cc:     Jakub Kicinski <jakub.kicinski@...ronome.com>,
        "David S. Miller" <davem@...emloft.net>,
        Alexandre Belloni <alexandre.belloni@...tlin.com>,
        Vivien Didelot <vivien.didelot@...il.com>,
        Joergen Andreasen <joergen.andreasen@...rochip.com>,
        "Allan W. Nielsen" <allan.nielsen@...rochip.com>,
        Horatiu Vultur <horatiu.vultur@...rochip.com>,
        Claudiu Manoil <claudiu.manoil@....com>,
        netdev <netdev@...r.kernel.org>,
        Vladimir Oltean <vladimir.oltean@....com>
Subject: Re: [PATCH net-next 15/15] net: mscc: ocelot: don't hardcode the
 number of the CPU port



On 11/10/2019 9:33 AM, Vladimir Oltean wrote:
> On Sun, 10 Nov 2019 at 19:12, Andrew Lunn <andrew@...n.ch> wrote:
>>
>> On Sun, Nov 10, 2019 at 07:00:33PM +0200, Vladimir Oltean wrote:
>>> On Sun, 10 Nov 2019 at 18:50, Andrew Lunn <andrew@...n.ch> wrote:
>>>>
>>>> On Sat, Nov 09, 2019 at 03:03:01PM +0200, Vladimir Oltean wrote:
>>>>> From: Vladimir Oltean <vladimir.oltean@....com>
>>>>>
>>>>> VSC7514 is a 10-port switch with 2 extra "CPU ports" (targets in the
>>>>> queuing subsystem for terminating traffic locally).
>>>>
>>>> So maybe that answers my last question.
>>>>
>>>>> There are 2 issues with hardcoding the CPU port as #10:
>>>>> - It is not clear which snippets of the code are configuring something
>>>>>   for one of the CPU ports, and which snippets are just doing something
>>>>>   related to the number of physical ports.
>>>>> - Actually any physical port can act as a CPU port connected to an
>>>>>   external CPU (in addition to the local CPU). This is called NPI mode
>>>>>   (Node Processor Interface) and is the way that the 6-port VSC9959
>>>>>   (Felix) switch is integrated inside NXP LS1028A (the "local management
>>>>>   CPU" functionality is not used there).
>>>>
>>>> So i'm having trouble reading this and spotting the difference between
>>>> the DSA concept of a CPU port and the two extra "CPU ports". Maybe
>>>> using the concept of virtual ports would help?
>>>>
>>>> Are the physical ports number 0-9, and so port #10 is the first extra
>>>> "CPU port", aka a virtual port? And so that would not work for DSA,
>>>> where you need a physical port.
>>>>
>>>>       Andrew
>>>
>>> Right. See my other answer which links to Ocelot documentation.
>>
>> Yes, i'm getting the picture now.
>>
>> The basic problem is that in the Linux kernel CPU port has a specific
>> meaning, and it is clashing with the meaning used in the datasheet. So
>> maybe in the driver, we need to refer to these two ports as 'local
>> ports'?
>>
> 
> Hmm, I don't know. Both types of CPU ports lead to management CPUs,
> but to different types of them. I understand the clash with the DSA
> meaning, but even if I rename it I would have to provide an
> explanation relative to the datasheet definitions (and I already
> explain that the NPI mode is the DSA type of CPU port). I'm not sure
> there is a net gain.

Maybe we need to agree on renaming DSA's CPU port to "mgmt_port" or
something that indicates that there is in-band signaling to help support
the function of managing the switch, incidentally Broadcom switches call
their ports In-Band Management Port (IMP) which is clearer IMHO.
-- 
Florian