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

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Message-ID: <20250822034202.26896-4-Smita.KoralahalliChannabasappa@amd.com>
Date: Fri, 22 Aug 2025 03:41:59 +0000
From: Smita Koralahalli <Smita.KoralahalliChannabasappa@....com>
To: <linux-cxl@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	<nvdimm@...ts.linux.dev>, <linux-fsdevel@...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>, Yao Xingtao <yaoxt.fnst@...itsu.com>,
	Peter Zijlstra <peterz@...radead.org>, Greg KH <gregkh@...uxfoundation.org>,
	Nathan Fontenot <nathan.fontenot@....com>, Smita Koralahalli
	<Smita.KoralahalliChannabasappa@....com>, Terry Bowman
	<terry.bowman@....com>, Robert Richter <rrichter@....com>, Benjamin Cheatham
	<benjamin.cheatham@....com>, PradeepVineshReddy Kodamati
	<PradeepVineshReddy.Kodamati@....com>, Zhijian Li <lizhijian@...itsu.com>
Subject: [PATCH 3/6] dax/hmem, cxl: Tighten dependencies on DEV_DAX_CXL and dax_hmem

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. 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.

Signed-off-by: Smita Koralahalli <Smita.KoralahalliChannabasappa@....com>
Signed-off-by: Dan Williams <dan.j.williams@...el.com>
---
 drivers/dax/Kconfig     | 2 ++
 drivers/dax/hmem/hmem.c | 2 +-
 2 files changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/dax/Kconfig b/drivers/dax/Kconfig
index d656e4c0eb84..3683bb3f2311 100644
--- a/drivers/dax/Kconfig
+++ b/drivers/dax/Kconfig
@@ -48,6 +48,8 @@ config DEV_DAX_CXL
 	tristate "CXL DAX: direct access to CXL RAM regions"
 	depends on CXL_BUS && CXL_REGION && DEV_DAX
 	default CXL_REGION && DEV_DAX
+	depends on CXL_ACPI >= DEV_DAX_HMEM
+	depends on CXL_PCI >= DEV_DAX_HMEM
 	help
 	  CXL RAM regions are either mapped by platform-firmware
 	  and published in the initial system-memory map as "System RAM", mapped
diff --git a/drivers/dax/hmem/hmem.c b/drivers/dax/hmem/hmem.c
index 9277e5ea0019..7ada820cb177 100644
--- a/drivers/dax/hmem/hmem.c
+++ b/drivers/dax/hmem/hmem.c
@@ -66,7 +66,7 @@ static int hmem_register_device(struct device *host, int target_nid,
 	long id;
 	int rc;
 
-	if (IS_ENABLED(CONFIG_CXL_REGION) &&
+	if (IS_ENABLED(CONFIG_DEV_DAX_CXL) &&
 	    region_intersects(res->start, resource_size(res), IORESOURCE_MEM,
 			      IORES_DESC_CXL) != REGION_DISJOINT) {
 		dev_dbg(host, "deferring range to CXL: %pr\n", res);
-- 
2.17.1