Re: [PATCH v6 03/11] powerpc/powernv: Detect supported IMC units and its events

[Anju T Sudhakar]

Hi Michael,


On Thursday 13 April 2017 05:13 PM, Michael Ellerman wrote:
> Anju T Sudhakar <anju@xxxxxxxxxxxxxxxxxx> writes:
> > On Thursday 06 April 2017 02:07 PM, Stewart Smith wrote:
> > > Madhavan Srinivasan <maddy@xxxxxxxxxxxxxxxxxx> writes:
> > > > --- a/arch/powerpc/platforms/powernv/opal-imc.c
> > > > +++ b/arch/powerpc/platforms/powernv/opal-imc.c
> > > > @@ -33,6 +33,388 @@
> > > <snip>
> > > > +static void imc_pmu_setup(struct device_node *parent)
> > > > +{
> > > > +	struct device_node *child;
> > > > +	int pmu_count = 0, rc = 0;
> > > > +	const struct property *pp;
> > > > +
> > > > +	if (!parent)
> > > > +		return;
> > > > +
> > > > +	/* Setup all the IMC pmus */
> > > > +	for_each_child_of_node(parent, child) {
> > > > +		pp = of_get_property(child, "compatible", NULL);
> > > > +		if (pp) {
> > > > +			/*
> > > > +			 * If there is a node with a "compatible" field,
> > > > +			 * that's a PMU node
> > > > +			 */
> > > > +			rc = imc_pmu_create(child, pmu_count);
> > > > +			if (rc)
> > > > +				return;
> > > > +			pmu_count++;
> > > > +		}
> > > > +	}
> > > > +}
> > > This doesn't strike me as the right kind of structure, the presence of a
> > > compatible property really just says "hey, there's this device and it's
> > > compatible with these ways of accessing it".
> > >
> > > I'm guessing the idea behind having imc-nest-offset/size in a top level
> > > node is because it's common to everything under it and the aim is to not
> > > blow up the device tree to be enormous.
> > >
> > > So why not go after each ibm,imc-counters-nest compatible node under the
> > > top level ibm,opal-in-memory-counters node? (i'm not convinced that
> > > having ibm,ibmc-counters-nest versus ibm,imc-counters-core and
> > > ibm,imc-counters-thread as I see in the dts is correct though, as
> > > they're all accessed exactly the same way?)
> > The idea here is, we have one directory which contains common events
> > information for nest(same incase of core and thread), and one directory
> > for each nest(/core/thread) pmu.
> > So while parsing we need to make sure that the node which we are parsing
> > is the pmu node, not the node which contains the common event
> > information. We use the "compatible" property here for that purpose.
> > Because we don't have a compatible property for the node which contains
> > events info.
> That's a really bad hack.
>
> You can use the compatible property to detect the node you're looking
> for, but you need to look at the *value* of the property and check it's
> what you expect. Just checking that it's there is fragile.
>
> cheers



ok. I will rework this code.



Thanks,
Anju