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

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Date:   Mon, 16 Jan 2023 09:08:37 +0100
From:   Clément Léger <clement.leger@...tlin.com>
To:     Vladimir Oltean <olteanv@...il.com>
Cc:     Andrew Lunn <andrew@...n.ch>, Jakub Kicinski <kuba@...nel.org>,
        Florian Fainelli <f.fainelli@...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

Le Fri, 13 Jan 2023 17:37:30 +0200,
Vladimir Oltean <olteanv@...il.com> a écrit :

> On Fri, Jan 13, 2023 at 03:12:40PM +0100, Andrew Lunn wrote:
> > 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.  
> 
> That being said, port_vlan_add(), port_vlan_del() and port_vlan_filtering()
> are all serialized by the rtnl_lock().

Ok then, I'll remove this lock and rely on the RTNL lock.

Thanks,

-- 
Clément Léger,
Embedded Linux and Kernel engineer at Bootlin
https://bootlin.com