Re: [PATCH] powerpc: Use nid as fallback for chip_id

[Srikar Dronamraju <srikar@linux.vnet.ibm.com>]

* Michael Ellerman <mpe@ellerman.id.au> [2019-07-29 22:41:55]:

> >  
> > +	chip_id = of_get_ibm_chip_id(np);
> > +	if (chip_id == -1)
> > +		chip_id = of_node_to_nid(np);
> > +
> >  	of_node_put(np);
> > -	return of_get_ibm_chip_id(np);
> > +	return chip_id;
> >  }
> 
> A nid is not a chip-id.
> 

Agree that nid is not a chip-id.

> This obviously happens to work for the case you've identified above but
> it's not something I'm happy to merge in general.
> 

Okay.

> We could do a similar change in the topology code, but I'd probably like
> it to be restricted to when we're running under PowerVM and there are no
> chip-ids found at all.
> 

So for PowerNV case and KVM guest, of_get_ibm_chip_id() always seems to
returns a valid chip-id. Its *only* in the PowerVM case that we are
returning nid as the fallback chip-id.


Do you think checking for OPAL firmware would help?

chip_id = of_get_ibm_chip_id(np);
if (chip_id == -1 && !firmware_has_feature(FW_FEATURE_OPAL))
	chip_id = of_node_to_nid(np);

of_node_put(np);


or should we do

int topology_physical_package_id(int cpu)
{
	int chip_id = cpu_to_chip_id(cpu)
	if (chip_id == -1 && !firmware_has_feature(FW_FEATURE_OPAL))
		//Fallback to nid instead of chip-id.
....
	return chip_id;
}

> I'm also not clear how it will interact with migration.
> 

On migration, this function would be triggered when the cpumasks are getting
updated. So I would expect this to continue working.

Or Am I missing someother migration related quirk?

> cheers
> 


The other alternative that I see is 




-- 
Thanks and Regards
Srikar Dronamraju