On Mon, Aug 17, 2015 at 8:01 AM, Christoph Hellwig <hch@xxxxxx> wrote: > On Sat, Aug 15, 2015 at 09:04:02AM -0700, Dan Williams wrote: >> What other layer? /sys/devices/platform/e820_pmem is that exact same >> device we had before this patch. We just have a proper driver for it >> now. > > We're adding another layer of indirection between the old e820 file > and the new module. Ok, yes, I was confused by "another layer of platform_devices". That said here are the non-unit-test related reasons for this change that I would include in a new changelog: --- We currently register a platform device for e820 type-12 memory and register a nvdimm bus beneath it. Registering the platform device triggers the device-core machinery to probe for a driver, but that search currently comes up empty. Building the nvdimm-bus registration into the e820_pmem platform device registration in this way forces libnvdimm to be built-in. Instead, convert the built-in portion of CONFIG_X86_PMEM_LEGACY to simply register a platform device and move the rest of the logic to the driver for e820_pmem, for the following reasons: 1/ Letting libnvdimm be a module allows building and testing libnvdimm.ko changes without rebooting 2/ All the normal policy around modules can be applied to e820_pmem (unbind to disable and/or blacklisting the module from loading by default) 3/ Moving the driver to a generic location and converting it to scan "iomem_resource" rather than "e820.map" means any other architecture can take advantage of this simple nvdimm resource discovery mechanism by registering a resource named "Persistent Memory (legacy)" -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>