On Tue, Apr 28, 2015 at 3:21 PM, Phil Pokorny
On Tue, Apr 28, 2015 at 2:04 PM, Andy Lutomirski
> On Tue, Apr 28, 2015 at 11:25 AM, Dan Williams <dan.j.williams(a)intel.com>
>> +config ND_E820
>> + tristate "E820: Support the E820-type-12 PMEM convention"
>> + depends on X86_PMEM_LEGACY
>> + default m if X86_PMEM_LEGACY
>> + select LIBND
>> + help
>> + Prior to ACPI 6 some platforms advertised peristent memory
>> + via type-12 e820 memory ranges. Create a libnd bus and
>> + attach an instance of the pmem driver to these ranges.
> How about something like:
> "This driver allows libnd to work with legacy, pre-ACPI 6 NVDIMMs.
> This enables such devices to be exposed as block devices using PMEM.
> The legacy NVDIMM interface is problematic. This driver will not work
> if you boot using UEFI, and some NVDIMMs and motherboards that work
> with this driver may require proprietary code in order to work
Perhaps not "problematic" but "requires a BIOS in Legacy mode"
It might also mention that if you use the kernel command line
memmap=nn!ss syntax it adds
a type 12 region to the e820 map and so you would want this support.
If you have a motherboard with UEFI support for NVDIMM's that would be
This is such a mess that I think this driver should maybe flat-out
refuse to load in this type of configuration without some scary module
option. I have some NVDIMMs that report as type 12 but need two extra
out-of-tree drivers to work safely. First, they need i2c_imc or the
equivalent (I'll try to resubmit that soon). Second, they need secret
magic NDAed register poking. The latter is very problematic.
At the very least, I think we should discourage people who don't
really know what they're doing from using this driver without care.