Re: CXL 1.1 Support Plan

["Verma, Vishal L" <vishal.l.verma@intel.com>]

On Thu, 2021-09-30 at 22:17 +0000, John Groves wrote:
> > > 
> I don't see your doc patch yet in the ndctl repo, but I recommend merging it there.
> 
> A related question: "daxctl reconfigure-device --mode=system-ram ..." works for me,
> with --force, but going the other way (--mode=devdax) fails.  But a reboot puts it back
> into devdax mode regardless of the pre-boot setting (i.e. --mode=system-ram reverts
> back to devdax on reboot).

Oh, I'm a bit confused. --force only applies when going from system-ram
to devdax -- it offlines the memory for you. Without force, you're
responsible for a prior 'daxctl offline-memory daxX.Y' step.

Going from devdax to system-ram should not need --force, and I don't
think force actually does anything there.

> 
> Is reconfigure-device capable of remaining in effect after a reboot (in which case I'm curious
> how you persist the info if the device is volatile; I believe it's the LSA on a non-volatile
> device).

The beginnings of this automation are in progress, at least for
converting pmem devices:

  https://lore.kernel.org/nvdimm/20210831090459.2306727-1-vishal.l.verma@intel.com/

This is yet to be extended to volatile dax devices after figuring out
what property we can key off of - one idea is the 'target_node' from
ACPI.

> 
> Back to the patch: you mention --mode=system-ram, but it might be helpful to add
> a mention of --mode=devdax, along with a mention of whether (and how) these
> changes are persisted.

The rest of the man page talks a little bit about the modes:

  https://pmem.io/ndctl/daxctl-reconfigure-device.html

Dan - you haven't posted the patch you attached to the list yet have
you? /me couldn't find it on lore - wasn't sure if I'd just missed it.