[PATCH v2] libnvdimm: Update persistence domain value for of_pmem and papr_scm device

[Dan Williams]

On Tue, Feb 4, 2020 at 9:21 PM Aneesh Kumar K.V
<aneesh.kumar at linux.ibm.com> wrote:
>
> Currently, kernel shows the below values
>         "persistence_domain":"cpu_cache"
>         "persistence_domain":"memory_controller"
>         "persistence_domain":"unknown"
>
> "cpu_cache" indicates no extra instructions is needed to ensure the persistence
> of data in the pmem media on power failure.
>
> "memory_controller" indicates platform provided instructions need to be issued

No, it does not. The only requirement implied by "memory_controller"
is global visibility outside the cpu cache. If there are special
instructions beyond that then it isn't persistent memory, at least not
pmem that is safe for dax. virtio-pmem is an example of pmem-like
memory that is not enabled for userspace flushing (MAP_SYNC disabled).

> as per documented sequence to make sure data get flushed so that it is
> guaranteed to be on pmem media in case of system power loss.
>
> Based on the above use memory_controller for non volatile regions on ppc64.
>
> Signed-off-by: Aneesh Kumar K.V <aneesh.kumar at linux.ibm.com>
> ---
>  arch/powerpc/platforms/pseries/papr_scm.c | 7 ++++++-
>  drivers/nvdimm/of_pmem.c                  | 4 +++-
>  include/linux/libnvdimm.h                 | 1 -
>  3 files changed, 9 insertions(+), 3 deletions(-)
>
> diff --git a/arch/powerpc/platforms/pseries/papr_scm.c b/arch/powerpc/platforms/pseries/papr_scm.c
> index 7525635a8536..ffcd0d7a867c 100644
> --- a/arch/powerpc/platforms/pseries/papr_scm.c
> +++ b/arch/powerpc/platforms/pseries/papr_scm.c
> @@ -359,8 +359,13 @@ static int papr_scm_nvdimm_init(struct papr_scm_priv *p)
>
>         if (p->is_volatile)
>                 p->region = nvdimm_volatile_region_create(p->bus, &ndr_desc);
> -       else
> +       else {
> +               /*
> +                * We need to flush things correctly to guarantee persistance
> +                */

There are never guarantees. If you're going to comment what does
software need to flush, and how?

> +               set_bit(ND_REGION_PERSIST_MEMCTRL, &ndr_desc.flags);
>                 p->region = nvdimm_pmem_region_create(p->bus, &ndr_desc);
> +       }
>         if (!p->region) {
>                 dev_err(dev, "Error registering region %pR from %pOF\n",
>                                 ndr_desc.res, p->dn);
> diff --git a/drivers/nvdimm/of_pmem.c b/drivers/nvdimm/of_pmem.c
> index 8224d1431ea9..6826a274a1f1 100644
> --- a/drivers/nvdimm/of_pmem.c
> +++ b/drivers/nvdimm/of_pmem.c
> @@ -62,8 +62,10 @@ static int of_pmem_region_probe(struct platform_device *pdev)
>
>                 if (is_volatile)
>                         region = nvdimm_volatile_region_create(bus, &ndr_desc);
> -               else
> +               else {
> +                       set_bit(ND_REGION_PERSIST_MEMCTRL, &ndr_desc.flags);
>                         region = nvdimm_pmem_region_create(bus, &ndr_desc);
> +               }
>
>                 if (!region)
>                         dev_warn(&pdev->dev, "Unable to register region %pR from %pOF\n",
> diff --git a/include/linux/libnvdimm.h b/include/linux/libnvdimm.h
> index 0f366706b0aa..771d888a5ed7 100644
> --- a/include/linux/libnvdimm.h
> +++ b/include/linux/libnvdimm.h
> @@ -54,7 +54,6 @@ enum {
>         /*
>          * Platform provides mechanisms to automatically flush outstanding
>          * write data from memory controler to pmem on system power loss.
> -        * (ADR)

I'd rather not delete critical terminology for a developer / platform
owner to be able to consult documentation, or their vendor. Can you
instead add the PowerPC equivalent term for this capability? I.e. list
(x86: ADR PowerPC: foo ...).