netdev - Re: [PATCH net-next] net: dsa: rzn1-a5psw: Add vlan support

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Date:   Fri, 13 Jan 2023 15:12:40 +0100
From:   Andrew Lunn <andrew@...n.ch>
To:     Jakub Kicinski <kuba@...nel.org>
Cc:     Clément Léger <clement.leger@...tlin.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        Vladimir Oltean <olteanv@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Paolo Abeni <pabeni@...hat.com>,
        Russell King <linux@...linux.org.uk>,
        linux-renesas-soc@...r.kernel.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Thomas Petazzoni <thomas.petazzoni@...tlin.com>,
        Herve Codina <herve.codina@...tlin.com>,
        Miquèl Raynal <miquel.raynal@...tlin.com>,
        Milan Stevanovic <milan.stevanovic@...com>,
        Jimmy Lalande <jimmy.lalande@...com>,
        Pascal Eberhard <pascal.eberhard@...com>
Subject: Re: [PATCH net-next] net: dsa: rzn1-a5psw: Add vlan support

On Thu, Jan 12, 2023 at 09:37:55PM -0800, Jakub Kicinski wrote:
> On Wed, 11 Jan 2023 12:56:07 +0100 Clément Léger wrote:
> > Add support for vlan operation (add, del, filtering) on the RZN1
> > driver. The a5psw switch supports up to 32 VLAN IDs with filtering,
> > tagged/untagged VLANs and PVID for each ports.
> 
> noob question - do you need that mutex? 
> aren't those ops all under rtnl_lock?

Hi Jakub

Not commenting about this specific patch, but not everything in DSA is
done under RTNL. So you need to deal with some parallel API calls. But
they tend to be in different areas. I would not expect to see two VLAN
changes as the same time, but maybe VLAN and polling in a workqueue to
update the statistics for example could happen. Depending on the
switch, some protect might be needed to stop these operations
interfering with each other. And DSA drivers in general tend to KISS
and over lock. Nothing here is particularly hot path, the switch
itself is on the end of a slow bus, so the overhead of locks are
minimum.

	Andrew