Re: [Linux-nvdimm] [PATCH v2 05/20] libnd, nd_acpi: dimm/memory-devices

On Fri, 2015-05-01 at 11:43 -0700, Dan Williams wrote: > On Fri, May 1, 2015 at 11:19 AM, Toshi Kani <toshi.kani(a)hp.com&gt; wrote: > > On Fri, 2015-05-01 at 11:22 -0700, Dan Williams wrote: > >> On Fri, May 1, 2015 at 10:48 AM, Toshi Kani <toshi.kani(a)hp.com&gt; wrote: > >> > On Tue, 2015-04-28 at 14:24 -0400, Dan Williams wrote: > >> >> Register the memory devices described in the nfit as libnd 'dimm' > >> >> devices on an nd bus. The kernel assigned device id for dimms is > >> >> dynamic. If userspace needs a more static identifier it should consult > >> >> a provider-specific attribute. In the case where NFIT is the provider, > >> >> the 'nmemX/nfit/handle' or 'nmemX/nfit/serial' attributes may be used > >> >> for this purpose. > >> > : > >> >> + > >> >> +static int nd_acpi_register_dimms(struct acpi_nfit_desc *acpi_desc) > >> >> +{ > >> >> + struct nfit_mem *nfit_mem; > >> >> + > >> >> + list_for_each_entry(nfit_mem, &acpi_desc->dimms, list) { > >> >> + struct nd_dimm *nd_dimm; > >> >> + unsigned long flags = 0; > >> >> + u32 nfit_handle; > >> >> + > >> >> + nfit_handle = __to_nfit_memdev(nfit_mem)->nfit_handle; > >> >> + nd_dimm = nd_acpi_dimm_by_handle(acpi_desc, nfit_handle); > >> >> + if (nd_dimm) { > >> >> + /* > >> >> + * If for some reason we find multiple DCRs the > >> >> + * first one wins > >> >> + */ > >> >> + dev_err(acpi_desc->dev, "duplicate DCR detected: %s\n", > >> >> + nd_dimm_name(nd_dimm)); > >> >> + continue; > >> >> + } > >> >> + > >> >> + if (nfit_mem->bdw && nfit_mem->memdev_pmem) > >> >> + flags |= NDD_ALIASING; > >> > > >> > Does this check work for a NVDIMM card which has multiple pmem regions > >> > with label info, but does not have any bdw region configured? > >> > >> If you have multiple pmem regions then you don't have aliasing and > >> don't need a label. You'll get an nd_namespace_io per region. > >> > >> > The code assumes that namespace_pmem (NDD_ALIASING) and namespace_blk > >> > have label info. There may be an NVDIMM card with a single blk region > >> > without label info. > >> > >> I'd really like to suggest that labels are only for resolving aliasing > >> and that if you have a BLK-only NVDIMM you'll get an automatic > >> namespace created the same as a PMEM-only. Partitioning is always > >> there to provide sub-divisions of a namespace. The only reason to > >> support multiple BLK-namespaces per-region is to give each a different > >> sector size. I may eventually need to relent on this position, but > >> I'd really like to understand the use case for requiring labels when > >> aliasing is not present as it seems like a waste to me. > > > > By looking at the callers of is_namespace_pmem() and is_namespace_blk(), > > such as nd_namespace_label_update(), I am concerned that the namespace > > types are also used for indicating the presence a label. Is it OK for > > nd_namespace_label_update() to do nothing when there is no aliasing? Did you forget to answer this question? I am not asking to have a label. I am asking if the namespace types can handle it correctly. Restating the nd_namespace_label_update() example: - namespace_io case: Skip, but a label may still exist. Correct? - namespace_blk case: Proceed, but blk does not require a label.