netdev - Re: [PATCH net 6/8] net: mscc: ocelot: make struct ocelot_stat

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Date:   Wed, 17 Aug 2022 15:07:45 -0700
From:   Colin Foster <colin.foster@...advantage.com>
To:     Vladimir Oltean <vladimir.oltean@....com>
Cc:     "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        Andrew Lunn <andrew@...n.ch>,
        Vivien Didelot <vivien.didelot@...il.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        Claudiu Manoil <claudiu.manoil@....com>,
        Alexandre Belloni <alexandre.belloni@...tlin.com>,
        "UNGLinuxDriver@...rochip.com" <UNGLinuxDriver@...rochip.com>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Maxim Kochetkov <fido_max@...ox.ru>
Subject: Re: [PATCH net 6/8] net: mscc: ocelot: make struct
 ocelot_stat_layout array indexable

On Wed, Aug 17, 2022 at 10:03:51PM +0000, Vladimir Oltean wrote:
> On Wed, Aug 17, 2022 at 01:47:07PM -0700, Colin Foster wrote:
> > > How about we add this extra check?
> > > 
> > > diff --git a/drivers/net/ethernet/mscc/ocelot_stats.c b/drivers/net/ethernet/mscc/ocelot_stats.c
> > > index d39908c1c6c9..85259de86ec2 100644
> > > --- a/drivers/net/ethernet/mscc/ocelot_stats.c
> > > +++ b/drivers/net/ethernet/mscc/ocelot_stats.c
> > > @@ -385,7 +385,7 @@ EXPORT_SYMBOL(ocelot_port_get_stats64);
> > >  static int ocelot_prepare_stats_regions(struct ocelot *ocelot)
> > >  {
> > >  	struct ocelot_stats_region *region = NULL;
> > > -	unsigned int last;
> > > +	unsigned int last = 0;
> > >  	int i;
> > >  
> > >  	INIT_LIST_HEAD(&ocelot->stats_regions);
> > > @@ -402,6 +402,12 @@ static int ocelot_prepare_stats_regions(struct ocelot *ocelot)
> > >  			if (!region)
> > >  				return -ENOMEM;
> > >  
> > > +			/* enum ocelot_stat must be kept sorted in the same
> > > +			 * order as ocelot->stats_layout[i].reg in order to
> > > +			 * have efficient bulking.
> > > +			 */
> > > +			WARN_ON(last >= ocelot->stats_layout[i].reg);
> > > +
> > >  			region->base = ocelot->stats_layout[i].reg;
> > >  			region->count = 1;
> > >  			list_add_tail(&region->node, &ocelot->stats_regions);
> > > 
> > > If not, help me understand the concern better.
> > 
> > You get my concern. That's a good comment / addition. Gaps are welcome
> > in the register layout, but moving backwards will ensure (in the current
> > implementation) inefficiencies.
> 
> Ok. The WARN_ON() won't trigger with current code. Do you mind if I add
> it as a net-next change, and don't resend this series for net? I'm
> worried I'll miss this week's "net" pull request which means I'll have
> to wait some more for the other rework surrounding stats handling in the
> ocelot driver (which in turn is a dependency for frame preemption).

No objections here.

I'll respond in more detail to your other points in a separate email.
Might not be able to craft a response today.