Re: [Linux-nvdimm] [PATCH v2 02/20] libnd, nd_acpi: initial libnd infrastructure and NFIT support

On Thu, Apr 30, 2015 at 6:21 PM, Rafael J. Wysocki <rjw(a)rjwysocki.net&gt; wrote: > On Thursday, April 30, 2015 05:39:06 PM Dan Williams wrote: >> On Thu, Apr 30, 2015 at 4:23 PM, Rafael J. Wysocki <rjw(a)rjwysocki.net&gt; wrote: [..] >> >> +if ND_DEVICES >> >> + >> >> +config LIBND >> >> + tristate "LIBND: libnd device driver support" >> >> + help >> >> + Platform agnostic device model for a libnd bus. Publishes >> >> + resources for a PMEM (persistent-memory) driver and/or BLK >> >> + (sliding mmio window(s)) driver to attach. Exposes a device >> >> + topology under a "ndX" bus device, a "/dev/ndctlX" bus-ioctl >> >> + message passing interface, and a "/dev/nmemX" dimm-ioctl >> >> + message interface for each memory device registered on the >> >> + bus. instance. A userspace library "ndctl" provides an API >> >> + to enumerate/manage this subsystem. >> >> + >> >> +config ND_ACPI >> >> + tristate "ACPI: NFIT to libnd bus support" >> >> + select LIBND >> >> + depends on ACPI >> >> + help >> >> + Infrastructure to probe ACPI 6 compliant platforms for >> >> + NVDIMMs (NFIT) and register a libnd device tree. In >> >> + addition to storage devices this also enables libnd craft >> >> + ACPI._DSM messages for platform/dimm configuration. >> > >> > I'm wondering if the two CONFIG options above really need to be user-selectable? >> > >> > For example, what reason people (who've already selected ND_DEVICES) may have >> > for not selecting ND_ACPI if ACPI is set? >> >> >> Later on in the series we introduce ND_E820 which supports creating a >> libnd-bus from e820-type-12 memory ranges on pre-NFIT systems. I'm >> also considering a configfs defined libnd-bus because e820 types are >> not nearly enough information to safely define nvdimm resources >> outside of NFIT. > > I hope these are not mutually exclusive with ND_ACPI? Otherwise distros > will have problems with supporting them in one kernel. You can have ND_E820 support and ND_ACPI support in the same system. Likely an NFIT enabled system will never have e820-type-12 ranges, but if a user messes up and uses the new memmap=ss!nn command line to overlap NFIT-defined memory then the request_mem_region() calls in the driver will collide. First to load wins in that scenario. > If ND_E820 and ND_ACPI aren't mutually exclusive, I still don't see a good > enough reason for asking users about ND_ACPI. Why would I ever say "No" > here if I said "Yes" or "Module" to ND_DEVICES? I agree that if the user selects ND_DEVICES then ND_ACPI should probably default on, but otherwise turning it off is a useful option. If you know your system is pre-ACPI-6 then why bother including support?