Re: [PATCH v2] libnvdimm: Update persistence domain value for of_pmem and papr_scm device
From: Dan Williams <hidden>
Date: 2020-02-09 16:14:12
Also in:
nvdimm
On Tue, Feb 4, 2020 at 9:21 PM Aneesh Kumar K.V [off-list ref] 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 issuedNo, 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).
quoted hunk ↗ jump to hunk
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 <redacted> --- 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?
quoted hunk ↗ jump to hunk
+ 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 ...).