[PATCH v2] powerpc/papr_scm: Fix warning triggered by perf_stats_show()

[Michael Ellerman]

Vaibhav Jain <vaibhav at linux.ibm.com> writes:
> A warning is reported by the kernel in case perf_stats_show() returns
> an error code. The warning is of the form below:
>
>  papr_scm ibm,persistent-memory:ibm,pmemory at 44100001:
>  	  Failed to query performance stats, Err:-10
>  dev_attr_show: perf_stats_show+0x0/0x1c0 [papr_scm] returned bad count
>  fill_read_buffer: dev_attr_show+0x0/0xb0 returned bad count
>
> On investigation it looks like that the compiler is silently truncating the
> return value of drc_pmem_query_stats() from 'long' to 'int', since the
> variable used to store the return code 'rc' is an 'int'. This
> truncated value is then returned back as a 'ssize_t' back from
> perf_stats_show() to 'dev_attr_show()' which thinks of it as a large
> unsigned number and triggers this warning..
>
> To fix this we update the type of variable 'rc' from 'int' to
> 'ssize_t' that prevents the compiler from truncating the return value
> of drc_pmem_query_stats() and returning correct signed value back from
> perf_stats_show().
>
> Fixes: 2d02bf835e573 ('powerpc/papr_scm: Fetch nvdimm performance
>        stats from PHYP')

Please don't word wrap the Fixes tag it breaks b4.

I've fixed it up this time.

cheers