linux-kernel - Re: [PATCH 08/11] arm: perf: add functions to parse affinity from dt

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Message-ID: <20141117150253.GB25416@leverpostej>
Date:	Mon, 17 Nov 2014 15:02:53 +0000
From:	Mark Rutland <mark.rutland@....com>
To:	Will Deacon <will.deacon@....com>
Cc:	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"grant.likely@...aro.org" <grant.likely@...aro.org>,
	Rob Herring <rob.herring@...nel.org>
Subject: Re: [PATCH 08/11] arm: perf: add functions to parse affinity from dt

On Mon, Nov 17, 2014 at 11:16:25AM +0000, Will Deacon wrote:
> On Fri, Nov 07, 2014 at 04:25:33PM +0000, Mark Rutland wrote:
> > Depending on hardware configuration, some devices may only be accessible
> > from certain CPUs, may have interrupts wired up to a subset of CPUs, or
> > may have operations which affect subsets of CPUs. To handle these
> > devices it is necessary to describe this affinity information in
> > devicetree.
> > 
> > This patch adds functions to handle parsing the CPU affinity of
> > properties from devicetree, based on Lorenzo's topology binding,
> > allowing subsets of CPUs to be associated with interrupts, hardware
> > ports, etc. The functions can be used to build cpumasks and also to test
> > whether an affinity property only targets one CPU independent of the
> > current configuration (e.g. when the kernel supports fewer CPUs than are
> > physically present). This is useful for dealing with mixed SPI/PPI
> > devices.
> > 
> > A device may have an arbitrary number of affinity properties, the
> > meaning of which is device-specific and should be specified in a given
> > device's binding document.
> > 
> > For example, an affinity property describing interrupt routing may
> > consist of a phandle pointing to a subtree of the topology nodes,
> > indicating the set of CPUs an interrupt originates from or may be taken
> > on. Bindings may have restrictions on the topology nodes referenced -
> > for describing coherency controls an affinity property may indicate a
> > whole cluster (including any non-CPU logic it contains) is affected by
> > some configuration.
> > 
> > Signed-off-by: Mark Rutland <mark.rutland@....com>
> > Cc: Grant Likely <grant.likely@...aro.org>
> > Cc: Rob Herring <rob.herring@...nel.org>
> > ---
> >  arch/arm/kernel/perf_event_cpu.c | 127 +++++++++++++++++++++++++++++++++++++++
> >  1 file changed, 127 insertions(+)
> > 
> > diff --git a/arch/arm/kernel/perf_event_cpu.c b/arch/arm/kernel/perf_event_cpu.c
> > index ce35149..dfcaba5 100644
> > --- a/arch/arm/kernel/perf_event_cpu.c
> > +++ b/arch/arm/kernel/perf_event_cpu.c
> > @@ -22,6 +22,7 @@
> >  #include <linux/export.h>
> >  #include <linux/kernel.h>
> >  #include <linux/of.h>
> > +#include <linux/of_device.h>
> >  #include <linux/platform_device.h>
> >  #include <linux/slab.h>
> >  #include <linux/spinlock.h>
> > @@ -294,6 +295,132 @@ static int probe_current_pmu(struct arm_pmu *pmu)
> >  	return ret;
> >  }
> >  
> > +/*
> > + * Test if the node is within the topology tree.
> > + * Walk up to the root, keeping refcounts balanced.
> > + */
> > +static bool is_topology_node(struct device_node *node)
> > +{
> > +	struct device_node *np, *cpu_map;
> > +	bool ret = false;
> > +
> > +	cpu_map = of_find_node_by_path("/cpus/cpu-map");
> > +	if (!cpu_map)
> > +		return false;
> > +
> > +	/*
> > +	 * of_get_next_parent decrements the refcount of the provided node.
> > +	 * Increment it first to keep things balanced.
> > +	 */
> > +	for (np = of_node_get(node); np; np = of_get_next_parent(np)) {
> > +		if (np != cpu_map)
> > +			continue;
> > +
> > +		ret = true;
> > +		break;
> > +	}
> > +
> > +	of_node_put(np);
> > +	of_node_put(cpu_map);
> > +	return ret;
> > +}
> 
> Wouldn't this be more at home in topology.c, or somewhere where others can
> make use of it?

Perhaps. I'll need this for arm64 too and I don't know where that should
live.

Mark.
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