Re: [PATCH v2] powerpc/kernel/sysfs: Export ldbar spr to sysfs

[Anju T Sudhakar]

Hi mpe,


On Wednesday 01 November 2017 06:20 AM, Michael Ellerman wrote:
> Anju T Sudhakar <anju@xxxxxxxxxxxxxxxxxx> writes:
>
> > Add ldbar spr to sysfs. The spr will hold thread level In-Memory Collection (IMC)
> > counter configuration data.
> This is missing any justification for why we would want to expose this,
> and in particular why we would make it *writable*.
>
> cheers


Thank you for reviewing the patch.

LDBAR, holds the thread-level counter configuration. Exposing this will help
us to understand the current status of thread-level counters in the system.
Primarily, Bit 0 of ldbar tells whether the counters are enabled or not.
And bit 1Â tells the mode (if 0-Accumulation Mode/if 1-Trace Mode).

But regarding the permission, you are right. On a reassessment I think 
that the permission
should be read only, because it is possible that we may write an 
incorrect value to the ldbar, that is wrong.
So I will change the permission here.



Thanks,
Anju
> > diff --git a/arch/powerpc/kernel/sysfs.c b/arch/powerpc/kernel/sysfs.c
> > index 4437c70..f8caee0 100644
> > --- a/arch/powerpc/kernel/sysfs.c
> > +++ b/arch/powerpc/kernel/sysfs.c
> > @@ -485,6 +485,7 @@ SYSFS_PMCSETUP(mmcra, SPRN_MMCRA);
> >   SYSFS_SPRSETUP(purr, SPRN_PURR);
> >   SYSFS_SPRSETUP(spurr, SPRN_SPURR);
> >   SYSFS_SPRSETUP(pir, SPRN_PIR);
> > +SYSFS_SPRSETUP(ldbar, SPRN_LDBAR);
> >   
> >   /*
> >     Lets only enable read for phyp resources and
> > @@ -492,6 +493,7 @@ SYSFS_SPRSETUP(pir, SPRN_PIR);
> >     Lets be conservative and default to pseries.
> >   */
> >   static DEVICE_ATTR(mmcra, 0600, show_mmcra, store_mmcra);
> > +static DEVICE_ATTR(ldbar, 0600, show_ldbar, store_ldbar);
> >   static DEVICE_ATTR(spurr, 0400, show_spurr, NULL);
> >   static DEVICE_ATTR(purr, 0400, show_purr, store_purr);
> >   static DEVICE_ATTR(pir, 0400, show_pir, NULL);
> > @@ -757,6 +759,9 @@ static int register_cpu_online(unsigned int cpu)
> >   			device_create_file(s, &pmc_attrs[i]);
> >   
> >   #ifdef CONFIG_PPC64
> > +	if (cpu_has_feature(CPU_FTR_ARCH_300))
> > +		device_create_file(s, &dev_attr_ldbar);
> > +
> >   	if (cpu_has_feature(CPU_FTR_MMCRA))
> >   		device_create_file(s, &dev_attr_mmcra);
> >   
> > @@ -842,6 +847,9 @@ static int unregister_cpu_online(unsigned int cpu)
> >   			device_remove_file(s, &pmc_attrs[i]);
> >   
> >   #ifdef CONFIG_PPC64
> > +	if (cpu_has_feature(CPU_FTR_ARCH_300))
> > +		device_remove_file(s, &dev_attr_ldbar);
> > +
> >   	if (cpu_has_feature(CPU_FTR_MMCRA))
> >   		device_remove_file(s, &dev_attr_mmcra);
> >   
> > --
> > 2.7.4