Re: [PATCH 1/6] drivers/cxl: add cxl_memctrl_mode and region->memctrl

[Jonathan Cameron <jonathan.cameron@huawei.com>]

On Wed, 14 Jan 2026 13:25:53 -0500
Gregory Price <gourry@gourry.net> wrote:

> On Wed, Jan 14, 2026 at 05:18:08PM +0000, Jonathan Cameron wrote:
> > On Mon, 12 Jan 2026 11:35:09 -0500
> > Gregory Price <gourry@gourry.net> wrote:
> >   
> > > The CXL driver presently hands policy management over to DAX subsystem
> > > for sysram regions, which makes building policy around the entire region
> > > clunky and at time difficult (e.g. multiple actions to offline and
> > > hot-unplug memory reliably).
> > > 
> > > To support multiple backend controllers for memory regions (for example
> > > dax vs direct hotplug), implement a memctrl field in cxl_region allows
> > > switching uncomitted regions between different "memory controllers".
> > > 
> > > CXL_CONTROL_NONE: No selected controller, probe will fail.
> > > CXL_CONTROL_AUTO: If memory is already online as SysRAM, no controller
> > >                   otherwise register a dax_region
> > > CXL_CONTROL_DAX : register a dax_region
> > > 
> > > Auto regions will either be static sysram (BIOS-onlined) and has no
> > > region controller associated with it - or if the SP bit was set a
> > > DAX device will be created.
> > > 
> > > Rather than default all regions to the auto-controller, only default
> > > auto-regions to the auto controller.
> > > 
> > > Non-auto regions will be defaulted to CXL_CONTROL_NONE, which will cause
> > > a failure to probe unless a controller is selected.
> > > 
> > > Signed-off-by: Gregory Price <gourry@gourry.net>  
> > Trivial comments whilst I try to get my head around the series.
> > 
> > ...
> >  
> 
> Recommend piviting to v2 which simplifies and addresses some of your
> notes here already:
> 
> https://lore.kernel.org/linux-cxl/aWfe-r7uEV-ajfhX@gourry-fedora-PF4VCD3F/T/#m791301178876f9b1ab55ed4091c674d4f4ceb07c
> 
> Still need to add some docs.
That came cover letter free so I didn't figure out it was this
until a few patches in!

J
> 
> ~Gregory