Re: [RFC PATCH v2] powerpc/papr_scm: Move duplicate definitions to common header files

Hi Mpe,

Thanks for looking into this patch.

Michael Ellerman [off-list ref] writes:

Shivaprasad G Bhat [off-list ref] writes:

quoted

papr_scm and ndtest share common PDSM payload structs like
nd_papr_pdsm_health. Presently these structs are duplicated across papr_pdsm.h
and ndtest.h header files. Since 'ndtest' is essentially arch independent and can
run on platforms other than PPC64, a way needs to be deviced to avoid redundancy
and duplication of PDSM structs in future.

So the patch proposes moving the PDSM header from arch/powerpc/include/uapi/ to
the generic include/uapi/linux directory. Also, there are some #defines common
between papr_scm and ndtest which are not exported to the user space. So, move
them to a header file which can be shared across ndtest and papr_scm via newly
introduced include/linux/papr_scm.h.

Signed-off-by: Shivaprasad G Bhat <redacted>
Signed-off-by: Vaibhav Jain <redacted>
Suggested-by: "Aneesh Kumar K.V" <redacted>
---
Changelog:

Since v1:
Link: https://patchwork.kernel.org/project/linux-nvdimm/patch/162505488483.72147.12741153746322191381.stgit@56e104a48989/
* Removed dependency on this patch for the other patches

 MAINTAINERS                               |    2 
 arch/powerpc/include/uapi/asm/papr_pdsm.h |  165 -----------------------------
 arch/powerpc/platforms/pseries/papr_scm.c |   43 --------
 include/linux/papr_scm.h                  |   48 ++++++++
 include/uapi/linux/papr_pdsm.h            |  165 +++++++++++++++++++++++++++++

This doesn't make sense to me.

Anything with papr (or PAPR) in the name is fundamentally powerpc
specific, it doesn't belong in a generic header, or in a generic
location.

What's the actual problem you're trying to solve?

The ndtest module (tools/testing/nvdimm/test/ndtest.c) is implemented in
an arch independed way to enable testing of PAPR PDSMs on non ppc64
platforms like x86_64. It uses the same PDSM structs as used by papr_scm
to communicate with libndctl userspace. 

Since papr_scm is ppc64 arch specific we were so far duplicating the
PDSM structures between ndtest and papr_scm. The patch tries to solve
this duplication by moving the shared structs to arch independent common
include dirs.

Secondly, PDSMs describes how userspace can use NVDIMM_FAMILY_PAPR to
interact with NVDIMMs. So potentially a new NVDIMM beyond powerpc arch
can add its support and would need access to the same structs used by
papr_scm and ndtest. In that context it would make sense to move PDSM
headers to generic include dirs.

If it's just including papr_scm bits into ndtest.c then that should be
as simple as:

#ifdef __powerpc__
#include <asm/papr_scm.h>
#endif

Shouldn't it?

No, as ndtest implements support for NVDIMM_FAMILY_PAPR and would need
access to PDSM related structs which presently are only available for
powerpc.

cheers

-- 
Cheers
~ Vaibhav