Re: [PATCH v2] powerpc/papr_scm: Reduce error severity if nvdimm stats inaccessible

Hi Ira,

Thanks for looking into this patch

Ira Weiny [off-list ref] writes:

On Thu, May 06, 2021 at 12:46:06AM +0530, Vaibhav Jain wrote:

quoted

Currently drc_pmem_qeury_stats() generates a dev_err in case
"Enable Performance Information Collection" feature is disabled from
HMC or performance stats are not available for an nvdimm. The error is
of the form below:

papr_scm ibm,persistent-memory:ibm,pmemory@44104001: Failed to query
	 performance stats, Err:-10

This error message confuses users as it implies a possible problem
with the nvdimm even though its due to a disabled/unavailable
feature. We fix this by explicitly handling the H_AUTHORITY and
H_UNSUPPORTED errors from the H_SCM_PERFORMANCE_STATS hcall.

In case of H_AUTHORITY error an info message is logged instead of an
error, saying that "Permission denied while accessing performance
stats". Also '-EACCES' error is return instead of -EPERM.

I thought you clarified before that this was a permission issue.  So why change
the error to EACCES?

EACCESS("Permission Denied") felt like a more accurate error code for
this case than EPERM("Operation not permitted"). So switched the usage
of EPERM error code to handle the case if this hcall is not supported
for an nvdimm.

quoted

In case of H_UNSUPPORTED error we return a -EPERM error back from
drc_pmem_query_stats() indicating that performance stats-query
operation is not supported on this nvdimm.

EPERM seems wrong here too...  ENOTSUP?

Yes, will change it to EOPNOTSUPP in v3.

Ira
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-- 
Cheers
~ Vaibhav