linux-kernel - Re: [PATCH 4/6] cxl: add CONFIG_CXL_REGION_CTRL_AUTO

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Message-ID: <6965cabc68fda_875d100c0@dwillia2-mobl4.notmuch>
Date: Mon, 12 Jan 2026 20:31:56 -0800
From: <dan.j.williams@...el.com>
To: Gregory Price <gourry@...rry.net>, "Cheatham, Benjamin"
	<benjamin.cheatham@....com>
CC: <linux-cxl@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	<kernel-team@...a.com>, <dave@...olabs.net>, <jonathan.cameron@...wei.com>,
	<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 4/6] cxl: add CONFIG_CXL_REGION_CTRL_AUTO_* build config
 options

Gregory Price wrote:
[..]
> > If you remove the 'auto' mode earlier on, then you can just drop the first sentence here.
> > I'd also add a note about when a DAX region can be failed to be created (i.e. BIOS already
> > set up and onlined the memory).
> > 
> 
> I think I'm just going to drop this entirely, probably this was just too
> ambitious trying to create an easy transition from dax to sysram for
> auto regions.
> 
> The reality is BIOS-configured decoders "is NOT the way" (TM). If BIOS
> configures it - it's DAX, otherwise the user gets a choice (or they can
> tear it down and rebuild).

Is the plan here to "whither struct memory_block"? I can see value in
starting the deprecation process given the problems Hannes points out
and BIOS alignment causes massive numbers of those things to show up.

If yes, then even if it is DAX the distro might still want the option to
only allows for region-scoped "hotplug" rather than memory_block-scoped
"online".