linux-kernel - Re: [PATCH v8 5/8] arm64: Use of_cpu_node_to

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Message-ID: <20171017161140.GD19711@arm.com>
Date:   Tue, 17 Oct 2017 17:11:40 +0100
From:   Will Deacon <will.deacon@....com>
To:     Mark Rutland <mark.rutland@....com>
Cc:     Suzuki K Poulose <suzuki.poulose@....com>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        robh@...nel.org, sudeep.holla@....com, frowand.list@...il.com,
        devicetree@...r.kernel.org, Jonathan.Cameron@...wei.com,
        marc.zyngier@....com, peterz@...radead.org,
        mathieu.poirier@...aro.org, leo.yan@...aro.org,
        Catalin Marinas <catalin.marinas@....com>
Subject: Re: [PATCH v8 5/8] arm64: Use of_cpu_node_to_id helper for CPU
 topology parsing

On Tue, Oct 17, 2017 at 04:24:23PM +0100, Mark Rutland wrote:
> On Tue, Oct 10, 2017 at 11:33:00AM +0100, Suzuki K Poulose wrote:
> > Make use of the new generic helper to convert an of_node of a CPU
> > to the logical CPU id in parsing the topology.
> > 
> > Cc: Catalin Marinas <catalin.marinas@....com>
> > Cc: Leo Yan <leo.yan@...aro.org>
> > Cc: Will Deacon <will.deacon@....com>
> > Cc: Mark Rutland <mark.rutland@....com>
> > Signed-off-by: Suzuki K Poulose <suzuki.poulose@....com>
> 
> This looks sane to me, but it will need an ack from Will or Catalin.
> 
> FWIW:
> 
> Acked-by: Mark Rutland <mark.rutland@....com>
> 
> Thanks,
> Mark.
> 
> > ---
> >  arch/arm64/kernel/topology.c | 16 ++++++----------
> >  1 file changed, 6 insertions(+), 10 deletions(-)
> > 
> > diff --git a/arch/arm64/kernel/topology.c b/arch/arm64/kernel/topology.c
> > index 8d48b233e6ce..21868530018e 100644
> > --- a/arch/arm64/kernel/topology.c
> > +++ b/arch/arm64/kernel/topology.c
> > @@ -37,18 +37,14 @@ static int __init get_cpu_for_node(struct device_node *node)
> >  	if (!cpu_node)
> >  		return -1;
> >  
> > -	for_each_possible_cpu(cpu) {
> > -		if (of_get_cpu_node(cpu, NULL) == cpu_node) {
> > -			topology_parse_cpu_capacity(cpu_node, cpu);
> > -			of_node_put(cpu_node);
> > -			return cpu;
> > -		}
> > -	}
> > -
> > -	pr_crit("Unable to find CPU node for %pOF\n", cpu_node);
> > +	cpu = of_cpu_node_to_id(cpu_node);
> > +	if (cpu >= 0)
> > +		topology_parse_cpu_capacity(cpu_node, cpu);
> > +	else
> > +		pr_crit("Unable to find CPU node for %pOF\n", cpu_node);
> >  
> >  	of_node_put(cpu_node);

This of_node_put is confusing me. Since of_cpu_node_to_id appears to be
balanced with its use of the node refcount, is this one intended to pair
with the earlier call to of_parse_phandle? If so, does that mainline is
currently broken here because it doesn't drop the refcount twice for the
matching node? Or do we need to return with that held?

Will