linux-kernel - [PATCH v3 4/9] cxl/mem: Skip intermediate port enumeration of restricted endpoints (RCDs)

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Message-ID: <20221109104059.766720-5-rrichter@amd.com>
Date:   Wed, 9 Nov 2022 11:40:54 +0100
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>,
        Ben Widawsky <bwidawsk@...nel.org>,
        Dan Williams <dan.j.williams@...el.com>
CC:     <linux-cxl@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Len Brown <lenb@...nel.org>,
        Jonathan Cameron <Jonathan.Cameron@...wei.com>,
        "Davidlohr Bueso" <dave@...olabs.net>,
        Dave Jiang <dave.jiang@...el.com>,
        Robert Richter <rrichter@....com>
Subject: [PATCH v3 4/9] cxl/mem: Skip intermediate port enumeration of restricted endpoints (RCDs)

When an endpoint is found, all ports in beetween the endpoint and the
CXL host bridge need to be created. In the RCH case there are no ports
in between a host bridge and the endpoint. Skip the enumeration of
intermediate ports.

The port enumeration does not only create all ports, it also
initializes the endpoint chain by adding the endpoint to every
downstream port up to the root bridge. This must be done also in RCD
mode, but is much more simple as the endpoint only needs to be added
to the host bridge's dport.

Note: For endpoint removal the cxl_detach_ep() is not needed as it is
released in cxl_port_release().

Signed-off-by: Robert Richter <rrichter@....com>
---
 drivers/cxl/core/port.c | 18 ++++++++++++++++--
 1 file changed, 16 insertions(+), 2 deletions(-)

diff --git a/drivers/cxl/core/port.c b/drivers/cxl/core/port.c
index d10c3580719b..e21a9c3fe4da 100644
--- a/drivers/cxl/core/port.c
+++ b/drivers/cxl/core/port.c
@@ -1366,8 +1366,24 @@ int devm_cxl_enumerate_ports(struct cxl_memdev *cxlmd)
 {
 	struct device *dev = &cxlmd->dev;
 	struct device *iter;
+	struct cxl_dport *dport;
+	struct cxl_port *port;
 	int rc;
 
+	/*
+	 * Skip intermediate port enumeration in the RCH case, there
+	 * are no ports in between a host bridge and an endpoint. Only
+	 * initialize the EP chain.
+	 */
+	if (is_cxl_restricted(cxlmd)) {
+		port = cxl_mem_find_port(cxlmd, &dport);
+		if (!port)
+			return -ENXIO;
+		rc = cxl_add_ep(dport, &cxlmd->dev);
+		put_device(&port->dev);
+		return rc;
+	}
+
 	rc = devm_add_action_or_reset(&cxlmd->dev, cxl_detach_ep, cxlmd);
 	if (rc)
 		return rc;
@@ -1381,8 +1397,6 @@ int devm_cxl_enumerate_ports(struct cxl_memdev *cxlmd)
 	for (iter = dev; iter; iter = grandparent(iter)) {
 		struct device *dport_dev = grandparent(iter);
 		struct device *uport_dev;
-		struct cxl_dport *dport;
-		struct cxl_port *port;
 
 		if (!dport_dev)
 			return 0;
-- 
2.30.2