linux-kernel - [PATCH v1 08/20] cxl/region: Rework memregion id allocation and move it to register

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Message-ID: <20250715191143.1023512-9-rrichter@amd.com>
Date: Tue, 15 Jul 2025 21:11:31 +0200
From: Robert Richter <rrichter@....com>
To: 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>, Jonathan Cameron <Jonathan.Cameron@...wei.com>,
	Dave Jiang <dave.jiang@...el.com>, Davidlohr Bueso <dave@...olabs.net>
CC: <linux-cxl@...r.kernel.org>, <linux-kernel@...r.kernel.org>, Gregory Price
	<gourry@...rry.net>, "Fabio M. De Francesco"
	<fabio.m.de.francesco@...ux.intel.com>, Terry Bowman <terry.bowman@....com>,
	Robert Richter <rrichter@....com>
Subject: [PATCH v1 08/20] cxl/region: Rework memregion id allocation and move it to register_region()

Make the atomic_cmpxchg() loop an inner loop of register_region().
Simplify calling of __create_region() by modifying the @port_id
function argument to accept a value of -1 to indicates that an
available memregion id should be assigned to the region.

Signed-off-by: Robert Richter <rrichter@....com>
---
 drivers/cxl/core/region.c | 31 ++++++++++++++++++++++---------
 1 file changed, 22 insertions(+), 9 deletions(-)

diff --git a/drivers/cxl/core/region.c b/drivers/cxl/core/region.c
index 57ee758bdece..34ffd726859e 100644
--- a/drivers/cxl/core/region.c
+++ b/drivers/cxl/core/region.c
@@ -2504,18 +2504,34 @@ static int register_region(struct cxl_region *cxlr, int id)
 {
 	struct cxl_root_decoder *cxlrd = cxlr->cxlrd;
 	struct device *dev = &cxlr->dev;
-	int rc;
+	int old, match, rc;
 
 	rc = memregion_alloc(GFP_KERNEL);
 	if (rc < 0)
 		return rc;
 
-	if (atomic_cmpxchg(&cxlrd->region_id, id, rc) != id) {
+	if (id < 0)
+		match = atomic_read(&cxlrd->region_id);
+	else
+		match = id;
+
+	for (; match >= 0;) {
+		old = atomic_cmpxchg(&cxlrd->region_id, match, rc);
+		if (old == match)
+			break;
+		if (id >= 0)
+			break;
+		match = old;
+	}
+
+	if (match < 0 || match != old) {
 		memregion_free(rc);
+		if (match < 0)
+			return -ENXIO;
 		return -EBUSY;
 	}
 
-	cxlr->id = id;
+	cxlr->id = old;
 
 	rc = dev_set_name(dev, "region%d", cxlr->id);
 	if (rc)
@@ -2528,7 +2544,8 @@ static int register_region(struct cxl_region *cxlr, int id)
  * devm_cxl_add_region - Adds a region to the CXL hierarchy.
  * @cxlr: region to be added
  * @id: memregion id to create must match current @port_id of the
- *      region's @cxlrd
+ *      region's @cxlrd. A negative value indicates that an available
+ *      memregion id should be assigned to the region.
  *
  * This is the second step of region initialization. Regions exist within an
  * address space which is mapped by a @cxlrd.
@@ -3412,11 +3429,7 @@ static struct cxl_region *construct_region(struct cxl_root_decoder *cxlrd,
 	int rc, part = READ_ONCE(cxled->part);
 	struct cxl_region *cxlr;
 
-	do {
-		cxlr = __create_region(cxlrd, cxlds->part[part].mode,
-				       atomic_read(&cxlrd->region_id));
-	} while (IS_ERR(cxlr) && PTR_ERR(cxlr) == -EBUSY);
-
+	cxlr = __create_region(cxlrd, cxlds->part[part].mode, -1);
 	if (IS_ERR(cxlr)) {
 		dev_err(cxlmd->dev.parent,
 			"%s:%s: %s failed assign region: %ld\n",
-- 
2.39.5