linux-kernel - Re: [PATCH 3/6] dax/hmem, cxl: Tighten dependencies on DEV_DAX_CXL and dax

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Message-ID: <e95590e9-5c39-430b-bccd-e531d46c2228@fujitsu.com>
Date: Mon, 1 Sep 2025 03:28:30 +0000
From: "Zhijian Li (Fujitsu)" <lizhijian@...itsu.com>
To: Smita Koralahalli <Smita.KoralahalliChannabasappa@....com>,
	"linux-cxl@...r.kernel.org" <linux-cxl@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"nvdimm@...ts.linux.dev" <nvdimm@...ts.linux.dev>,
	"linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>
CC: Davidlohr Bueso <dave@...olabs.net>, Jonathan Cameron
	<jonathan.cameron@...wei.com>, Dave Jiang <dave.jiang@...el.com>, Alison
 Schofield <alison.schofield@...el.com>, Vishal Verma
	<vishal.l.verma@...el.com>, Ira Weiny <ira.weiny@...el.com>, Dan Williams
	<dan.j.williams@...el.com>, 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>, "Xingtao Yao (Fujitsu)"
	<yaoxt.fnst@...itsu.com>, Peter Zijlstra <peterz@...radead.org>, Greg KH
	<gregkh@...uxfoundation.org>, Nathan Fontenot <nathan.fontenot@....com>,
	Terry Bowman <terry.bowman@....com>, Robert Richter <rrichter@....com>,
	Benjamin Cheatham <benjamin.cheatham@....com>, PradeepVineshReddy Kodamati
	<PradeepVineshReddy.Kodamati@....com>
Subject: Re: [PATCH 3/6] dax/hmem, cxl: Tighten dependencies on DEV_DAX_CXL
 and dax_hmem



On 22/08/2025 11:41, Smita Koralahalli wrote:
> Update Kconfig and runtime checks to better coordinate dax_cxl and dax_hmem
> registration.
> 
> Add explicit Kconfig ordering so that CXL_ACPI and CXL_PCI must be
> initialized before DEV_DAX_HMEM. 

Is this dependency statement fully accurate? To clarify, another prerequisite for
this ordering to work correctly is that dax_hmem must explicitly call
`request_module("cxl_acpi")` and `request_module("cxl_pci")` during its initialization.
  
Therefore, I recommend consolidating the following patches into a single commit
to ensure atomic handling of the initialization order:
- [PATCH 2/6] dax/hmem: Request cxl_acpi and cxl_pci before walking Soft Reserved ranges
- [PATCH 3/6] dax/hmem, cxl: Tighten dependencies on DEV_DAX_CXL and dax_hmem

Thanks
Zhijian

> This prevents dax_hmem from consuming
> Soft Reserved ranges before CXL drivers have had a chance to claim them.
> 
> Replace IS_ENABLED(CONFIG_CXL_REGION) with IS_ENABLED(CONFIG_DEV_DAX_CXL)
> so the code more precisely reflects when CXL-specific DAX coordination is
> expected.
> 
> This ensures that ownership of Soft Reserved ranges is consistently
> handed off to the CXL stack when DEV_DAX_CXL is configured.