linux-kernel - Re: [PATCH net-next v2 3/7] net: ethernet: fs_enet: drop the .adjust_link custom fs

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Message-ID: <20240904175043.0f198836@fedora.home>
Date: Wed, 4 Sep 2024 17:50:43 +0200
From: Maxime Chevallier <maxime.chevallier@...tlin.com>
To: Andrew Lunn <andrew@...n.ch>
Cc: davem@...emloft.net, Pantelis Antoniou <pantelis.antoniou@...il.com>,
 Jakub Kicinski <kuba@...nel.org>, Eric Dumazet <edumazet@...gle.com>, Paolo
 Abeni <pabeni@...hat.com>, Russell King <linux@...linux.org.uk>, Christophe
 Leroy <christophe.leroy@...roup.eu>, Florian Fainelli
 <f.fainelli@...il.com>, Heiner Kallweit <hkallweit1@...il.com>,
 netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
 thomas.petazzoni@...tlin.com, Herve Codina <herve.codina@...tlin.com>,
 Simon Horman <horms@...nel.org>, linuxppc-dev@...ts.ozlabs.org
Subject: Re: [PATCH net-next v2 3/7] net: ethernet: fs_enet: drop the
 .adjust_link custom fs_ops

On Wed, 4 Sep 2024 14:36:58 +0200
Andrew Lunn <andrew@...n.ch> wrote:

> On Wed, Sep 04, 2024 at 10:27:11AM +0200, Maxime Chevallier wrote:
> > Hi Andrew,
> > 
> > On Fri, 30 Aug 2024 23:06:08 +0200
> > Andrew Lunn <andrew@...n.ch> wrote:
> >   
> > > > --- a/drivers/net/ethernet/freescale/fs_enet/fs_enet-main.c
> > > > +++ b/drivers/net/ethernet/freescale/fs_enet/fs_enet-main.c
> > > > @@ -649,12 +649,7 @@ static void fs_adjust_link(struct net_device *dev)
> > > >  	unsigned long flags;
> > > >  
> > > >  	spin_lock_irqsave(&fep->lock, flags);
> > > > -
> > > > -	if (fep->ops->adjust_link)
> > > > -		fep->ops->adjust_link(dev);
> > > > -	else
> > > > -		generic_adjust_link(dev);
> > > > -
> > > > +	generic_adjust_link(dev);
> > > >  	spin_unlock_irqrestore(&fep->lock, flags);    
> > > 
> > > Holding a spinlock is pretty unusual. We are in thread context, and
> > > the phydev mutex is held. Looking at generic_adjust_link, do any of
> > > the fep->foo variables actually need protecting, particularly from
> > > changes in interrupts context?  
> > 
> > Yes there are, the interrupt mask/event registers are being accessed
> > from the interrupt handler and the ->restart() hook. I can try to
> > rework this a bit for a cleaner interrupt handling, but I don't have
> > means to test this on all mac flavors (fec/fcc/scc) :(  
> 
> As far as i can see, none of the fep->old* members are accessed
> outside of fs_enet-main.c. There values are not important for the
> restart call. So the spinlock has nothing to do with adjust_link as
> such, but restart. So maybe narrow down the lock to just the restart
> call? But it is not a big issues, just unusual.

I agree with you on that, and this is actually what end-up happening in
the final phylink conversion patch (only the restart() call gets called
wthin the spinlock).

I'll however include a patch that does exactly what you suggest as part
of the phylink conversion, both to make the big port-to-phylink patch
smaller, but also to better document why we only need to care about the
restart() part, if that's ok :)

Thanks,

Maxime