netdev - Re: [patch net-next RFC 0/4] introduce infrastructure for support of switch chip datapath

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Message-ID: <20140327165550.GN2845@minipsycho.orion>
Date:	Thu, 27 Mar 2014 17:55:50 +0100
From:	Jiri Pirko <jiri@...nulli.us>
To:	Sergey Ryazanov <ryazanov.s.a@...il.com>
Cc:	Florian Fainelli <f.fainelli@...il.com>,
	Jamal Hadi Salim <jhs@...atatu.com>,
	Roopa Prabhu <roopa@...ulusnetworks.com>,
	Neil Horman <nhorman@...driver.com>,
	Thomas Graf <tgraf@...g.ch>, netdev <netdev@...r.kernel.org>,
	David Miller <davem@...emloft.net>,
	Andy Gospodarek <andy@...yhouse.net>,
	dborkman <dborkman@...hat.com>, ogerlitz <ogerlitz@...lanox.com>,
	jesse <jesse@...ira.com>, pshelar <pshelar@...ira.com>,
	azhou <azhou@...ira.com>, Ben Hutchings <ben@...adent.org.uk>,
	Stephen Hemminger <stephen@...workplumber.org>,
	jeffrey.t.kirsher@...el.com, vyasevic <vyasevic@...hat.com>,
	Cong Wang <xiyou.wangcong@...il.com>,
	John Fastabend <john.r.fastabend@...el.com>,
	Eric Dumazet <edumazet@...gle.com>,
	Scott Feldman <sfeldma@...ulusnetworks.com>,
	Lennert Buytenhek <buytenh@...tstofly.org>,
	Shrijeet Mukherjee <shm@...ulusnetworks.com>,
	Felix Fietkau <nbd@...nwrt.org>
Subject: Re: [patch net-next RFC 0/4] introduce infrastructure for support of
 switch chip datapath

Thu, Mar 27, 2014 at 03:10:24PM CET, ryazanov.s.a@...il.com wrote:
>Hi all,
>
>sorry for the intrusion, but let me place my 2 cents.
>
>2014-03-27 10:56 GMT+04:00 Jiri Pirko <jiri@...nulli.us>:
>> Wed, Mar 26, 2014 at 11:22:51PM CET, f.fainelli@...il.com wrote:
>>>2014-03-26 14:51 GMT-07:00 Jamal Hadi Salim <jhs@...atatu.com>:
>>>> On 03/26/14 14:14, Jiri Pirko wrote:
>>>>>
>>>>> Wed, Mar 26, 2014 at 06:58:32PM CET, f.fainelli@...il.com wrote:
>>>>>>
>>>>>> 2014-03-26 10:35 GMT-07:00 Jiri Pirko <jiri@...nulli.us>:
>>>>
>>>>
>>>>
>>>>>> You are right, sw1p0 and sw1p1 were meant to be, say LAN ports in my
>>>>>> example.
>>>>>>
>>>>>> I think there is an implicit convention that sw1 represents the
>>>>>> Ethernet switch port connected to the CPU Ethernet MAC, and that it is
>>>>>> always connected, hence there is no need to create a "fake" bridge to
>>>>>> link sw1 to eth0 for instance?
>>>>>
>>>>>
>>>>> I think you are kind of mixing apples and oranges (or I might be I'm not
>>>>> understanding you correctly).
>>>>> This is how I see it, sticking to the names you use in the example:
>>>>>
>>>>>              (sw1) (abstract place-holder netdev)
>>>>>            --------
>>>>>           switch chip                   CPU
>>>>>     -----------------------            ------
>>>>>     sw1p0 sw1p1 sw1p2 sw1p3             eth0
>>>>>       |     |     |     |                |
>>>>>      PHY   PHY   PHY    ------someMII-----
>>>>>
>>>>> You see that eth0 is the CPU part of the "connection" and sw1p3 is the
>>>>> switch part (port representation).
>>>>>
>>>>
>>>>
>>>> Florian - I am sure you explained this before; I just dont remember. Why
>>>> is there need to expose eth0? It seems to me sw1p0-3 are abstracted
>>>> already in the kernel and the "cpu port" is merely a control interface.
>>>
>>>eth0 corresponds to a CPU Ethernet MAC facing e.g: sw1p3 switch port.
>>>It is "regular" Ethernet driver connected to the switch without
>>>switch-specific logic. The goal is twofold:
>>>
>>>- allow any regular Ethernet driver to be connected to an external
>>>switch via e.g: MDIO/MDC or other without specific switch knowledge
>>>- represents accurately how the hardware is designed/connected
>>>
>>>but maybe, we can simplify and have e.g: sw1p3 and eth0 be the same interface...
>>
>> I believe that hawing both sw1p3 and eth0 is the correct way of
>> modelling this. sw1p3 is instance if switch chip driver representing the
>> actual port of a switch. eth0 is an instance of some other ordinary NIC
>> driver (8139too is my favorite :))
>>
>> This model allows to draw the exact picture.
>> Also, when you add the described possibility to use iplink to build
>> vlans, bridges whatever on the switch ports, it makes perfect sense to
>> have this model.
>>
>> Merging sw1p3 and eth0 would cause a loose of information and confusion.
>>
>
>CPU switch port and switch fabric itself should be configured in
>consistence with host, in first place I mean a set of VLANs. Also it
>should be mentioned that some generic knobs such as port rate and
>duplex mode are meaningless for CPU switch port and a lot of status
>information (rx/tx counters etc.) duplicates statistics of host
>interface which is connected to switch port. So there are no reasons
>to force user to configure this port manually, and automatic
>configuration of CPU switch port without exporting them as netdev
>seems as good approach.

How can you tell that certain port is connected to CPU? That is platform
specific. 

>
>-- 
>BR,
>Sergey
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