Re: [PATCH v8 5/8] arm64: Use of_cpu_node_to_id helper for CPU topology parsing

[Suzuki K Poulose]

On 17/10/17 17:11, Will Deacon wrote:
> 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@xxxxxxx>
> > > Cc: Leo Yan <leo.yan@xxxxxxxxxx>
> > > Cc: Will Deacon <will.deacon@xxxxxxx>
> > > Cc: Mark Rutland <mark.rutland@xxxxxxx>
> > > Signed-off-by: Suzuki K Poulose <suzuki.poulose@xxxxxxx>
> >
> > This looks sane to me, but it will need an ack from Will or Catalin.
> >
> > FWIW:
> >
> > Acked-by: Mark Rutland <mark.rutland@xxxxxxx>
> >
> > 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?

Yes.

 If so, does that mainline is
> currently broken here because it doesn't drop the refcount twice for the
> matching node?

No. This of_node_put is for the failure case where we couldn't match a CPU.
In the success case, it is dropped just before we return the result within
the loop.

Cheers
Suzuki


 Or do we need to return with that held?
> Will