linux-kernel - [PATCH v5 5/7] dax: Introduce dax_cxl

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Message-ID: <20260122045543.218194-6-Smita.KoralahalliChannabasappa@amd.com>
Date: Thu, 22 Jan 2026 04:55:41 +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: Ard Biesheuvel <ardb@...nel.org>, 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>,
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	<dave@...olabs.net>, Matthew Wilcox <willy@...radead.org>, Jan Kara
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	Peter Zijlstra <peterz@...radead.org>, Greg Kroah-Hartman
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	Terry Bowman <terry.bowman@....com>, Robert Richter <rrichter@....com>,
	Benjamin Cheatham <benjamin.cheatham@....com>, Zhijian Li
	<lizhijian@...itsu.com>, Borislav Petkov <bp@...en8.de>, Smita Koralahalli
	<Smita.KoralahalliChannabasappa@....com>, Tomasz Wolski
	<tomasz.wolski@...itsu.com>
Subject: [PATCH v5 5/7] dax: Introduce dax_cxl_mode for CXL coordination

Introduce dax_cxl_mode to coordinate between dax_cxl and dax_hmem when
handling CXL tagged memory ranges.

This patch defines the dax_cxl_mode enum and establishes a default policy.
Subsequent patches will wire this into dax_cxl and dax_hmem to decide
whether CXL tagged memory ranges should be deferred, registered or
dropped.

No functional changes.

Signed-off-by: Smita Koralahalli <Smita.KoralahalliChannabasappa@....com>
---
 drivers/dax/bus.c | 3 +++
 drivers/dax/bus.h | 8 ++++++++
 2 files changed, 11 insertions(+)

diff --git a/drivers/dax/bus.c b/drivers/dax/bus.c
index fde29e0ad68b..72bc5b76f061 100644
--- a/drivers/dax/bus.c
+++ b/drivers/dax/bus.c
@@ -24,6 +24,9 @@ DECLARE_RWSEM(dax_region_rwsem);
  */
 DECLARE_RWSEM(dax_dev_rwsem);
 
+enum dax_cxl_mode dax_cxl_mode = DAX_CXL_MODE_DEFER;
+EXPORT_SYMBOL_GPL(dax_cxl_mode);
+
 #define DAX_NAME_LEN 30
 struct dax_id {
 	struct list_head list;
diff --git a/drivers/dax/bus.h b/drivers/dax/bus.h
index cbbf64443098..a40cbbf1e26b 100644
--- a/drivers/dax/bus.h
+++ b/drivers/dax/bus.h
@@ -41,6 +41,14 @@ struct dax_device_driver {
 	void (*remove)(struct dev_dax *dev);
 };
 
+enum dax_cxl_mode {
+	DAX_CXL_MODE_DEFER,
+	DAX_CXL_MODE_REGISTER,
+	DAX_CXL_MODE_DROP,
+};
+
+extern enum dax_cxl_mode dax_cxl_mode;
+
 int __dax_driver_register(struct dax_device_driver *dax_drv,
 		struct module *module, const char *mod_name);
 #define dax_driver_register(driver) \
-- 
2.17.1