netdev - Re: [PATCH v3 net-next 3/9] net: mscc: ocelot: serialize access to the MAC table

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Date:   Fri, 22 Oct 2021 21:04:47 +0200
From:   Andrew Lunn <andrew@...n.ch>
To:     Vladimir Oltean <olteanv@...il.com>
Cc:     Florian Fainelli <f.fainelli@...il.com>,
        Vladimir Oltean <vladimir.oltean@....com>,
        netdev@...r.kernel.org, Vivien Didelot <vivien.didelot@...il.com>,
        UNGLinuxDriver@...rochip.com, DENG Qingfang <dqfext@...il.com>,
        Kurt Kanzenbach <kurt@...utronix.de>,
        Hauke Mehrtens <hauke@...ke-m.de>,
        Woojung Huh <woojung.huh@...rochip.com>,
        Sean Wang <sean.wang@...iatek.com>,
        Landen Chao <Landen.Chao@...iatek.com>,
        Alexandre Belloni <alexandre.belloni@...tlin.com>,
        George McCollister <george.mccollister@...il.com>,
        John Crispin <john@...ozen.org>,
        Aleksander Jan Bajkowski <olek2@...pl>,
        Egil Hjelmeland <privat@...l-hjelmeland.no>,
        Oleksij Rempel <o.rempel@...gutronix.de>,
        Prasanna Vengateshan <prasanna.vengateshan@...rochip.com>,
        Ansuel Smith <ansuelsmth@...il.com>,
        Alvin Šipraga <alsi@...g-olufsen.dk>
Subject: Re: [PATCH v3 net-next 3/9] net: mscc: ocelot: serialize access to
 the MAC table

On Fri, Oct 22, 2021 at 09:00:52PM +0300, Vladimir Oltean wrote:
> On Fri, Oct 22, 2021 at 10:34:04AM -0700, Florian Fainelli wrote:
> > On 10/22/21 10:27 AM, Vladimir Oltean wrote:
> > > DSA would like to remove the rtnl_lock from its
> > > SWITCHDEV_FDB_{ADD,DEL}_TO_DEVICE handlers, and the felix driver uses
> > > the same MAC table functions as ocelot.
> > > 
> > > This means that the MAC table functions will no longer be implicitly
> > > serialized with respect to each other by the rtnl_mutex, we need to add
> > > a dedicated lock in ocelot for the non-atomic operations of selecting a
> > > MAC table row, reading/writing what we want and polling for completion.
> > > 
> > > Signed-off-by: Vladimir Oltean <vladimir.oltean@....com>
> > > ---
> > >  drivers/net/ethernet/mscc/ocelot.c | 53 +++++++++++++++++++++++-------
> > >  include/soc/mscc/ocelot.h          |  3 ++
> > >  2 files changed, 44 insertions(+), 12 deletions(-)
> > > 
> > > diff --git a/drivers/net/ethernet/mscc/ocelot.c b/drivers/net/ethernet/mscc/ocelot.c
> > > index 4e5ae687d2e2..72925529b27c 100644
> > > --- a/drivers/net/ethernet/mscc/ocelot.c
> > > +++ b/drivers/net/ethernet/mscc/ocelot.c
> > > @@ -20,11 +20,13 @@ struct ocelot_mact_entry {
> > >  	enum macaccess_entry_type type;
> > >  };
> > >  
> > > +/* Must be called with &ocelot->mact_lock held */
> > 
> > I don't know if the sparse annotations: __must_hold() would work here,
> > but if they do, they serve as both comment and static verification,
> > might as well use them?
> 
> I've never come across that annotation before, thanks.
> I'll fix this and the other issue and resend once the build tests for
> this series finish.

If sparse cannot figure it out, mv88e6xxx has:

static void assert_reg_lock(struct mv88e6xxx_chip *chip)
{
        if (unlikely(!mutex_is_locked(&chip->reg_lock))) {
                dev_err(chip->dev, "Switch registers lock not held!\n");
                dump_stack();
        }
}

which is a bit heavier in weight, but the MDIO bus transaction will
dominate the time for such operations, not checking a mutex.

	 Andrew