[PATCH v5 2/2] cxl/pci: Add sysfs attribute for CXL 1.1 device link status

["Kobayashi,Daisuke" <kobayashi.da-06@fujitsu.com>]

Add sysfs attribute for CXL 1.1 device link status to the cxl pci device.

In CXL1.1, the link status of the device is included in the RCRB mapped to
the memory mapped register area. Critically, that arrangement makes the
link status and control registers invisible to existing PCI user tooling.

Export those registers via sysfs with the expectation that PCI user
tooling will alternatively look for these sysfs files when attempting to
access to these CXL 1.1 endpoints registers.

Signed-off-by: "Kobayashi,Daisuke" <kobayashi.da-06@fujitsu.com>
---
 drivers/cxl/pci.c | 98 +++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 98 insertions(+)

diff --git a/drivers/cxl/pci.c b/drivers/cxl/pci.c
index 2ff361e756d6..b2d8198ab532 100644
--- a/drivers/cxl/pci.c
+++ b/drivers/cxl/pci.c
@@ -786,6 +786,103 @@ static int cxl_event_config(struct pci_host_bridge *host_bridge,
 	return 0;
 }
 
+static ssize_t rcd_link_cap_show(struct device *dev,
+				   struct device_attribute *attr, char *buf)
+{
+	struct cxl_port *port;
+	struct cxl_dport *dport;
+	struct cxl_dev_state *cxlds = dev_get_drvdata(dev);
+	struct cxl_memdev *cxlmd = cxlds->cxlmd;
+	struct device *endpoint_parent;
+
+	port = cxl_mem_find_port(cxlmd, &dport);
+	if (!port)
+		return -EINVAL;
+
+	endpoint_parent = port->uport_dev;
+	if (!endpoint_parent)
+		return -ENXIO;
+
+	guard(device)(endpoint_parent);
+	if (!endpoint_parent->driver)
+		return -ENXIO;
+
+	return sysfs_emit(buf, "%x\n", dport->rcrb.rcd_lnkcap);
+}
+static DEVICE_ATTR_RO(rcd_link_cap);
+
+static ssize_t rcd_link_ctrl_show(struct device *dev,
+				   struct device_attribute *attr, char *buf)
+{
+	struct cxl_port *port;
+	struct cxl_dport *dport;
+	struct cxl_dev_state *cxlds = dev_get_drvdata(dev);
+	struct cxl_memdev *cxlmd = cxlds->cxlmd;
+	struct device *endpoint_parent;
+
+	port = cxl_mem_find_port(cxlmd, &dport);
+	if (!port)
+		return -EINVAL;
+
+	endpoint_parent = port->uport_dev;
+	if (!endpoint_parent)
+		return -ENXIO;
+
+	guard(device)(endpoint_parent);
+	if (!endpoint_parent->driver)
+		return -ENXIO;
+
+	return sysfs_emit(buf, "%x\n", dport->rcrb.rcd_lnkctrl);
+}
+static DEVICE_ATTR_RO(rcd_link_ctrl);
+
+static ssize_t rcd_link_status_show(struct device *dev,
+				   struct device_attribute *attr, char *buf)
+{
+	struct cxl_port *port;
+	struct cxl_dport *dport;
+	struct cxl_dev_state *cxlds = dev_get_drvdata(dev);
+	struct cxl_memdev *cxlmd = cxlds->cxlmd;
+	struct device *endpoint_parent;
+
+	port = cxl_mem_find_port(cxlmd, &dport);
+	if (!port)
+		return -EINVAL;
+
+	endpoint_parent = port->uport_dev;
+	if (!endpoint_parent)
+		return -ENXIO;
+
+	guard(device)(endpoint_parent);
+	if (!endpoint_parent->driver)
+		return -ENXIO;
+
+	return sysfs_emit(buf, "%x\n", dport->rcrb.rcd_lnkstatus);
+}
+static DEVICE_ATTR_RO(rcd_link_status);
+
+static struct attribute *cxl_rcd_attrs[] = {
+		&dev_attr_rcd_link_cap.attr,
+		&dev_attr_rcd_link_ctrl.attr,
+		&dev_attr_rcd_link_status.attr,
+		NULL
+};
+
+static umode_t cxl_rcd_visible(struct kobject *kobj,
+					  struct attribute *a, int n)
+{
+	struct device *dev = kobj_to_dev(kobj);
+	struct pci_dev *pdev = to_pci_dev(dev);
+
+	if (is_cxl_restricted(pdev))
+		return a->mode;
+
+	return 0;
+}
+
+static struct attribute_group cxl_rcd_group = {
+		.attrs = cxl_rcd_attrs,
+		.is_visible = cxl_rcd_visible,
+};
+__ATTRIBUTE_GROUPS(cxl_rcd);
+
 static int cxl_pci_probe(struct pci_dev *pdev, const struct pci_device_id *id)
 {
 	struct pci_host_bridge *host_bridge = pci_find_host_bridge(pdev->bus);
@@ -969,6 +1066,7 @@ static struct pci_driver cxl_pci_driver = {
 	.id_table		= cxl_mem_pci_tbl,
 	.probe			= cxl_pci_probe,
 	.err_handler		= &cxl_error_handlers,
+	.dev_groups		= cxl_rcd_groups,
 	.driver	= {
 		.probe_type	= PROBE_PREFER_ASYNCHRONOUS,
 	},
-- 
2.44.0