linux-kernel - [RFC PATCH 15/20] cxl: Add a routine to find cxl root decoder on cxl bus

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Message-Id: <1295226194.21750165382072.JavaMail.epsvc@epcpadp2new>
Date: Tue, 17 Jun 2025 18:09:39 +0530
From: Neeraj Kumar <s.neeraj@...sung.com>
To: dan.j.williams@...el.com, dave@...olabs.net,
	jonathan.cameron@...wei.com, dave.jiang@...el.com,
	alison.schofield@...el.com, vishal.l.verma@...el.com, ira.weiny@...el.com
Cc: a.manzanares@...sung.com, nifan.cxl@...il.com, anisa.su@...sung.com,
	vishak.g@...sung.com, krish.reddy@...sung.com, arun.george@...sung.com,
	alok.rathore@...sung.com, s.neeraj@...sung.com, neeraj.kernel@...il.com,
	linux-kernel@...r.kernel.org, linux-cxl@...r.kernel.org,
	nvdimm@...ts.linux.dev, gost.dev@...sung.com, cpgs@...sung.com
Subject: [RFC PATCH 15/20] cxl: Add a routine to find cxl root decoder on
 cxl bus

Add cxl_find_root_decoder to find root decoder on cxl bus. It is used to
find root decoder during region creation

Signed-off-by: Neeraj Kumar <s.neeraj@...sung.com>
---
 drivers/cxl/core/port.c | 26 ++++++++++++++++++++++++++
 drivers/cxl/cxl.h       |  1 +
 2 files changed, 27 insertions(+)

diff --git a/drivers/cxl/core/port.c b/drivers/cxl/core/port.c
index 2452f7c15b2d..94d9322b8e38 100644
--- a/drivers/cxl/core/port.c
+++ b/drivers/cxl/core/port.c
@@ -513,6 +513,32 @@ struct cxl_switch_decoder *to_cxl_switch_decoder(struct device *dev)
 }
 EXPORT_SYMBOL_NS_GPL(to_cxl_switch_decoder, "CXL");
 
+static int match_root_decoder(struct device *dev, void *data)
+{
+	return is_root_decoder(dev);
+}
+
+/**
+ * cxl_find_root_decoder() - find a cxl root decoder on cxl bus
+ * @port: any descendant port in root-cxl-port topology
+ */
+struct cxl_root_decoder *cxl_find_root_decoder(struct cxl_port *port)
+{
+	struct cxl_root *cxl_root __free(put_cxl_root) = find_cxl_root(port);
+	struct device *dev;
+
+	if (!cxl_root)
+		return NULL;
+
+	dev = device_find_child(&cxl_root->port.dev, NULL, match_root_decoder);
+
+	if (!dev)
+		return NULL;
+
+	return to_cxl_root_decoder(dev);
+}
+EXPORT_SYMBOL_NS_GPL(cxl_find_root_decoder, "CXL");
+
 static void cxl_ep_release(struct cxl_ep *ep)
 {
 	put_device(ep->ep);
diff --git a/drivers/cxl/cxl.h b/drivers/cxl/cxl.h
index 30c80e04cb27..2c6a782d0941 100644
--- a/drivers/cxl/cxl.h
+++ b/drivers/cxl/cxl.h
@@ -871,6 +871,7 @@ bool is_cxl_nvdimm_bridge(struct device *dev);
 int devm_cxl_add_nvdimm(struct cxl_port *parent_port, struct cxl_memdev *cxlmd);
 struct cxl_nvdimm_bridge *cxl_find_nvdimm_bridge(struct cxl_port *port);
 void cxl_region_discovery(struct cxl_port *port);
+struct cxl_root_decoder *cxl_find_root_decoder(struct cxl_port *port);
 
 #ifdef CONFIG_CXL_REGION
 bool is_cxl_pmem_region(struct device *dev);
-- 
2.34.1