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

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Message-ID: <20260114183633.0000410f@huawei.com>
Date: Wed, 14 Jan 2026 18:36:33 +0000
From: Jonathan Cameron <jonathan.cameron@...wei.com>
To: Gregory Price <gourry@...rry.net>
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, 14 Jan 2026 13:25:53 -0500
Gregory Price <gourry@...rry.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@...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.
That came cover letter free so I didn't figure out it was this
until a few patches in!

J
> 
> ~Gregory