netdev - Re: [PATCH net-next] net: dsa: mv88e6xxx: assert SMI lock

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Date:	Fri, 30 Oct 2015 17:11:31 -0400
From:	Vivien Didelot <vivien.didelot@...oirfairelinux.com>
To:	Andrew Lunn <andrew@...n.ch>
Cc:	netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
	kernel@...oirfairelinux.com,
	"David S. Miller" <davem@...emloft.net>,
	Florian Fainelli <f.fainelli@...il.com>,
	Guenter Roeck <linux@...ck-us.net>,
	Neil Armstrong <narmstrong@...libre.com>
Subject: Re: [PATCH net-next] net: dsa: mv88e6xxx: assert SMI lock

On Oct. Friday 30 (44) 10:01 PM, Andrew Lunn wrote:
> > > >  static int _mv88e6xxx_reg_read(struct dsa_switch *ds, int addr, int reg)
> > > >  {
> > > > -	struct mii_bus *bus = dsa_host_dev_to_mii_bus(ds->master_dev);
> > > > +	struct mii_bus *bus;
> > > >  	int ret;
> > > >  
> > > > +	assert_smi_lock(ds);
> > > > +
> > > > +	bus = dsa_host_dev_to_mii_bus(ds->master_dev);
> > > 
> > > Is this change of when bus is assigned actually required?
> > 
> > No, but I found not necessary to issue this "mdio_bus" lookup if the
> > lock is not held (see net/dsa/dsa.c:555). Do you prefer not to do that?
> 
> You are optimising for an error condition. If this optimisation saves
> anything, it means we have a locking bug!

Very good point, I'll get rid of that then.

> As a separate patch, i would do this lookup once in a setup function
> and save it away in ps. We just need to watch out for the probe
> register accesses.

Yes, I already put that on a todo list ;-)

> > Also are you OK with removing all the "Must be called with..." comments,
> 
> Yes, it will become a lot more clear when the kernel outputs a stack dump!

Good, sending a v2 right away then.

Thanks,
-v
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