cxl/region: Consolidate cxl_decoder_kill_region() and cxl_region_detach()

Both detach_target() and cxld_unregister() want to tear down a cxl_region
when an endpoint decoder is either detached or destroyed.

When a region is to be destroyed cxl_region_detach() releases
cxl_region_rwsem unbinds the cxl_region driver and re-acquires the rwsem.

This "reverse" locking pattern is difficult to reason about, not amenable
to scope-based cleanup, and the minor differences in the calling context of
detach_target() and cxld_unregister() currently results in the
cxl_decoder_kill_region() wrapper.

Introduce cxl_decoder_detach() to wrap a core __cxl_decoder_detach() that
serves both cases. I.e. either detaching a known position in a region
(interruptible), or detaching an endpoint decoder if it is found to be a
member of a region (uninterruptible).

Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: Jonathan Cameron <jonathan.cameron@huawei.com>
Cc: Dave Jiang <dave.jiang@intel.com>
Cc: Alison Schofield <alison.schofield@intel.com>
Cc: Vishal Verma <vishal.l.verma@intel.com>
Cc: Ira Weiny <ira.weiny@intel.com>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
Reviewed-by: Fabio M. De Francesco <fabio.m.de.francesco@linux.intel.com>
Reviewed-by: Dave Jiang <dave.jiang@intel.com>
Reviewed-by: Jonathan Cameron <jonathan.cameron@huawei.com>
Reviewed-by: Alison Schofield <alison.schofield@intel.com>
Reviewed-by: Davidlohr Bueso <dave@stgolabs.net>
Link: https://patch.msgid.link/20250711234932.671292-8-dan.j.williams@intel.com
Signed-off-by: Dave Jiang <dave.jiang@intel.com>

drivers/cxl/core/core.h

@@ -12,6 +12,11 @@ extern const struct device_type cxl_pmu_type;
 
 extern struct attribute_group cxl_base_attribute_group;
 
+enum cxl_detach_mode {
+	DETACH_ONLY,
+	DETACH_INVALIDATE,
+};
+
 #ifdef CONFIG_CXL_REGION
 extern struct device_attribute dev_attr_create_pmem_region;
 extern struct device_attribute dev_attr_create_ram_region;
@@ -20,7 +25,11 @@ extern struct device_attribute dev_attr_region;
 extern const struct device_type cxl_pmem_region_type;
 extern const struct device_type cxl_dax_region_type;
 extern const struct device_type cxl_region_type;
-void cxl_decoder_kill_region(struct cxl_endpoint_decoder *cxled);
+
+int cxl_decoder_detach(struct cxl_region *cxlr,
+		       struct cxl_endpoint_decoder *cxled, int pos,
+		       enum cxl_detach_mode mode);
+
 #define CXL_REGION_ATTR(x) (&dev_attr_##x.attr)
 #define CXL_REGION_TYPE(x) (&cxl_region_type)
 #define SET_CXL_REGION_ATTR(x) (&dev_attr_##x.attr),
@@ -48,7 +57,9 @@ static inline int cxl_get_poison_by_endpoint(struct cxl_port *port)
 {
 	return 0;
 }
-static inline void cxl_decoder_kill_region(struct cxl_endpoint_decoder *cxled)
+static inline int cxl_decoder_detach(struct cxl_region *cxlr,
+				     struct cxl_endpoint_decoder *cxled,
+				     int pos, enum cxl_detach_mode mode)
 {
 }
 static inline int cxl_region_init(void)

drivers/cxl/core/port.c

@@ -2001,12 +2001,9 @@ EXPORT_SYMBOL_NS_GPL(cxl_decoder_add, "CXL");
 
 static void cxld_unregister(void *dev)
 {
-	struct cxl_endpoint_decoder *cxled;
-
-	if (is_endpoint_decoder(dev)) {
-		cxled = to_cxl_endpoint_decoder(dev);
-		cxl_decoder_kill_region(cxled);
-	}
+	if (is_endpoint_decoder(dev))
+		cxl_decoder_detach(NULL, to_cxl_endpoint_decoder(dev), -1,
+				   DETACH_INVALIDATE);
 
 	device_unregister(dev);
 }

drivers/cxl/core/region.c

@@ -2135,27 +2135,43 @@ static int cxl_region_attach(struct cxl_region *cxlr,
 	return 0;
 }
 
-static int cxl_region_detach(struct cxl_endpoint_decoder *cxled)
+static struct cxl_region *
+__cxl_decoder_detach(struct cxl_region *cxlr,
+		     struct cxl_endpoint_decoder *cxled, int pos,
+		     enum cxl_detach_mode mode)
 {
-	struct cxl_port *iter, *ep_port = cxled_to_port(cxled);
-	struct cxl_region *cxlr = cxled->cxld.region;
 	struct cxl_region_params *p;
-	int rc = 0;
 
 	lockdep_assert_held_write(&cxl_region_rwsem);
 
-	if (!cxlr)
-		return 0;
+	if (!cxled) {
+		p = &cxlr->params;
 
-	p = &cxlr->params;
-	get_device(&cxlr->dev);
+		if (pos >= p->interleave_ways) {
+			dev_dbg(&cxlr->dev, "position %d out of range %d\n",
+				pos, p->interleave_ways);
+			return ERR_PTR(-ENXIO);
+		}
+
+		if (!p->targets[pos])
+			return NULL;
+		cxled = p->targets[pos];
+	} else {
+		cxlr = cxled->cxld.region;
+		if (!cxlr)
+			return NULL;
+		p = &cxlr->params;
+	}
+
+	if (mode == DETACH_INVALIDATE)
+		cxled->part = -1;
 
 	if (p->state > CXL_CONFIG_ACTIVE) {
 		cxl_region_decode_reset(cxlr, p->interleave_ways);
 		p->state = CXL_CONFIG_ACTIVE;
 	}
 
-	for (iter = ep_port; !is_cxl_root(iter);
+	for (struct cxl_port *iter = cxled_to_port(cxled); !is_cxl_root(iter);
 	     iter = to_cxl_port(iter->dev.parent))
 		cxl_port_detach_region(iter, cxlr, cxled);
 
@@ -2166,7 +2182,7 @@ static int cxl_region_detach(struct cxl_endpoint_decoder *cxled)
 		dev_WARN_ONCE(&cxlr->dev, 1, "expected %s:%s at position %d\n",
 			      dev_name(&cxlmd->dev), dev_name(&cxled->cxld.dev),
 			      cxled->pos);
-		goto out;
+		return NULL;
 	}
 
 	if (p->state == CXL_CONFIG_ACTIVE) {
@@ -2180,21 +2196,42 @@ static int cxl_region_detach(struct cxl_endpoint_decoder *cxled)
 		.end = -1,
 	};
 
-	/* notify the region driver that one of its targets has departed */
-	up_write(&cxl_region_rwsem);
-	device_release_driver(&cxlr->dev);
-	down_write(&cxl_region_rwsem);
-out:
-	put_device(&cxlr->dev);
-	return rc;
+	get_device(&cxlr->dev);
+	return cxlr;
 }
 
-void cxl_decoder_kill_region(struct cxl_endpoint_decoder *cxled)
+/*
+ * Cleanup a decoder's interest in a region. There are 2 cases to
+ * handle, removing an unknown @cxled from a known position in a region
+ * (detach_target()) or removing a known @cxled from an unknown @cxlr
+ * (cxld_unregister())
+ *
+ * When the detachment finds a region release the region driver.
+ */
+int cxl_decoder_detach(struct cxl_region *cxlr,
+		       struct cxl_endpoint_decoder *cxled, int pos,
+		       enum cxl_detach_mode mode)
 {
-	down_write(&cxl_region_rwsem);
-	cxled->part = -1;
-	cxl_region_detach(cxled);
+	struct cxl_region *detach;
+
+	/* when the decoder is being destroyed lock unconditionally */
+	if (mode == DETACH_INVALIDATE)
+		down_write(&cxl_region_rwsem);
+	else {
+		int rc = down_write_killable(&cxl_region_rwsem);
+
+		if (rc)
+			return rc;
+	}
+
+	detach = __cxl_decoder_detach(cxlr, cxled, pos, mode);
 	up_write(&cxl_region_rwsem);
+
+	if (detach) {
+		device_release_driver(&detach->dev);
+		put_device(&detach->dev);
+	}
+	return 0;
 }
 
 static int attach_target(struct cxl_region *cxlr,
@@ -2225,29 +2262,7 @@ static int attach_target(struct cxl_region *cxlr,
 
 static int detach_target(struct cxl_region *cxlr, int pos)
 {
-	struct cxl_region_params *p = &cxlr->params;
-	int rc;
-
-	rc = down_write_killable(&cxl_region_rwsem);
-	if (rc)
-		return rc;
-
-	if (pos >= p->interleave_ways) {
-		dev_dbg(&cxlr->dev, "position %d out of range %d\n", pos,
-			p->interleave_ways);
-		rc = -ENXIO;
-		goto out;
-	}
-
-	if (!p->targets[pos]) {
-		rc = 0;
-		goto out;
-	}
-
-	rc = cxl_region_detach(p->targets[pos]);
-out:
-	up_write(&cxl_region_rwsem);
-	return rc;
+	return cxl_decoder_detach(cxlr, NULL, pos, DETACH_ONLY);
 }
 
 static size_t store_targetN(struct cxl_region *cxlr, const char *buf, int pos,