linux-kernel - Re: [PATCH net] net: Have netpoll bring-up DSA management interface

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Date:   Tue, 20 Oct 2020 18:12:47 -0700
From:   Jakub Kicinski <kuba@...nel.org>
To:     Vladimir Oltean <olteanv@...il.com>
Cc:     Florian Fainelli <f.fainelli@...il.com>, netdev@...r.kernel.org,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Yunjian Wang <wangyunjian@...wei.com>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH net] net: Have netpoll bring-up DSA management interface

On Tue, 20 Oct 2020 00:19:16 +0300 Vladimir Oltean wrote:
> On Mon, Oct 19, 2020 at 02:03:40PM -0700, Florian Fainelli wrote:
> > > Completely crazy and outlandish idea, I know, but what's wrong with
> > > doing this in DSA?  
> > 
> > I really do not have a problem with that approach however other stacked
> > devices like 802.1Q do not do that. It certainly scales a lot better to
> > do this within DSA rather than sprinkling DSA specific knowledge
> > throughout the network stack. Maybe for "configuration less" stacked
> > devices such as DSA, 802.1Q (bridge ports?), bond etc. it would be
> > acceptable to ensure that the lower device is always brought up?  
> 
> For upper interfaces with more than one lower (bridge, bond) I'm not so
> sure. For uppers with a single lower (DSA, 8021q), it's pretty much a
> no-brainer to me. Question is, where to code this? I think it's ok to
> leave it in DSA, then 8021q could copy it as well if there was a need.

FWIW no strong preference here. Maybe I'd lean slightly towards
Florian's approach since we can go to the always upping the CPU netdev
from that, if we start with auto-upping CPU netdev - user space may
depend on that in general so we can't go back.

But up to you folks, this seems like a DSA-specific problem, vlans don't
get created before user space is up (AFAIK), so there is no compelling
reason to change them in my mind.

Florian for you patch specifially - can't we use
netdev_for_each_lower_dev()?