linux-kernel - Re: [PATCH v5 3/7] cxl/region: Skip decoder reset on detach for autodiscovered regions

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Message-ID: <697a7e8a815b_3095100e9@dwillia2-mobl4.notmuch>
Date: Wed, 28 Jan 2026 13:24:26 -0800
From: <dan.j.williams@...el.com>
To: Alejandro Lucero Palau <alucerop@....com>, <dan.j.williams@...el.com>,
	"Koralahalli Channabasappa, Smita" <skoralah@....com>, Jonathan Cameron
	<jonathan.cameron@...wei.com>, Smita Koralahalli
	<Smita.KoralahalliChannabasappa@....com>
CC: <linux-cxl@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	<nvdimm@...ts.linux.dev>, <linux-fsdevel@...r.kernel.org>,
	<linux-pm@...r.kernel.org>, Ard Biesheuvel <ardb@...nel.org>, "Alison
 Schofield" <alison.schofield@...el.com>, Vishal Verma
	<vishal.l.verma@...el.com>, Ira Weiny <ira.weiny@...el.com>, Yazen Ghannam
	<yazen.ghannam@....com>, Dave Jiang <dave.jiang@...el.com>, Davidlohr Bueso
	<dave@...olabs.net>, Matthew Wilcox <willy@...radead.org>, Jan Kara
	<jack@...e.cz>, "Rafael J . Wysocki" <rafael@...nel.org>, Len Brown
	<len.brown@...el.com>, Pavel Machek <pavel@...nel.org>, Li Ming
	<ming.li@...omail.com>, Jeff Johnson <jeff.johnson@....qualcomm.com>, "Ying
 Huang" <huang.ying.caritas@...il.com>, Yao Xingtao <yaoxt.fnst@...itsu.com>,
	Peter Zijlstra <peterz@...radead.org>, Greg Kroah-Hartman
	<gregkh@...uxfoundation.org>, Nathan Fontenot <nathan.fontenot@....com>,
	Terry Bowman <terry.bowman@....com>, Robert Richter <rrichter@....com>,
	Benjamin Cheatham <benjamin.cheatham@....com>, Zhijian Li
	<lizhijian@...itsu.com>, Borislav Petkov <bp@...en8.de>, Tomasz Wolski
	<tomasz.wolski@...itsu.com>
Subject: Re: [PATCH v5 3/7] cxl/region: Skip decoder reset on detach for
 autodiscovered regions

Alejandro Lucero Palau wrote:
[..]
> I have been trying to figure out how to preserve the decoders for Type2 
> auto discover regions since, I think, this was demanded after v22 sent 
> upstream. This patch/change is what I was looking for, and although I 
> did implement it in another way requiring "consensus", this one seems 
> good enough and already discussed and approved, so all good.
> 
> 
> However, I think it would be also interesting to give the Type2 driver 
> the option of resetting decoders as well, what I have been using for v22 
> and successfully tested. But this change will preclude that other 
> possibility, so, what about an option for clearing CXL_REGION_F_AUTO by 
> Type2 drivers? If you want this only to be done by admin/root, I guess a 
> module param would do it.

The expecation is that as long as "Fixed Device Configuration" is not
set then reconfiguration is possible. The best case is BIOS does not
create the ambiguity and leaves accelerators alone. The hard part is
that HPA space going back into a general CXL pool for other regions when
it is really earmarked for a singular use case.

So yes, a future helper for accelerator drivers to reclaim decoder
ownership from the platform seems reasonable, but the first hope is to
just have a BIOS switch / change to stop mapping accelerators and let
the OS handle it.