linux-kernel - Re: [PATCH 1/6] drivers/cxl: add cxl_memctrl

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Message-ID: <aWffsUbIx2DUefSS@gourry-fedora-PF4VCD3F>
Date: Wed, 14 Jan 2026 13:25:53 -0500
From: Gregory Price <gourry@...rry.net>
To: Jonathan Cameron <jonathan.cameron@...wei.com>
Cc: linux-cxl@...r.kernel.org, linux-kernel@...r.kernel.org,
	kernel-team@...a.com, dave@...olabs.net, dave.jiang@...el.com,
	alison.schofield@...el.com, vishal.l.verma@...el.com,
	ira.weiny@...el.com, dan.j.williams@...el.com
Subject: Re: [PATCH 1/6] drivers/cxl: add cxl_memctrl_mode and region->memctrl

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@...rry.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@...rry.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.

~Gregory