cxl/core: Emit modalias for CXL devices

In order to enable libkmod lookups for CXL device objects to their
corresponding module, add 'modalias' to the base attribute of CXL
devices.
Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Reviewed-by: Ben Widawsky <ben.widawsky@intel.com>
Link: https://lore.kernel.org/r/164298424120.3018233.15611905873808708542.stgit@dwillia2-desk3.amr.corp.intel.comSigned-off-by: Dan Williams <dan.j.williams@intel.com>

Documentation/ABI/testing/sysfs-bus-cxl

@@ -34,6 +34,15 @@ Description:
 		the same value communicated in the DEVTYPE environment variable
 		for uevents for devices on the "cxl" bus.
 
+What:		/sys/bus/cxl/devices/*/modalias
+Date:		December, 2021
+KernelVersion:	v5.18
+Contact:	linux-cxl@vger.kernel.org
+Description:
+		CXL device objects export the modalias attribute which mirrors
+		the same value communicated in the MODALIAS environment variable
+		for uevents for devices on the "cxl" bus.
+
 What:		/sys/bus/cxl/devices/portX/uport
 Date:		June, 2021
 KernelVersion:	v5.14

drivers/cxl/core/port.c

@@ -34,8 +34,25 @@ static ssize_t devtype_show(struct device *dev, struct device_attribute *attr,
 }
 static DEVICE_ATTR_RO(devtype);
 
+static int cxl_device_id(struct device *dev)
+{
+	if (dev->type == &cxl_nvdimm_bridge_type)
+		return CXL_DEVICE_NVDIMM_BRIDGE;
+	if (dev->type == &cxl_nvdimm_type)
+		return CXL_DEVICE_NVDIMM;
+	return 0;
+}
+
+static ssize_t modalias_show(struct device *dev, struct device_attribute *attr,
+			     char *buf)
+{
+	return sysfs_emit(buf, CXL_MODALIAS_FMT "\n", cxl_device_id(dev));
+}
+static DEVICE_ATTR_RO(modalias);
+
 static struct attribute *cxl_base_attributes[] = {
 	&dev_attr_devtype.attr,
+	&dev_attr_modalias.attr,
 	NULL,
 };
 
@@ -855,15 +872,6 @@ void cxl_driver_unregister(struct cxl_driver *cxl_drv)
 }
 EXPORT_SYMBOL_NS_GPL(cxl_driver_unregister, CXL);
 
-static int cxl_device_id(struct device *dev)
-{
-	if (dev->type == &cxl_nvdimm_bridge_type)
-		return CXL_DEVICE_NVDIMM_BRIDGE;
-	if (dev->type == &cxl_nvdimm_type)
-		return CXL_DEVICE_NVDIMM;
-	return 0;
-}
-
 static int cxl_bus_uevent(struct device *dev, struct kobj_uevent_env *env)
 {
 	return add_uevent_var(env, "MODALIAS=" CXL_MODALIAS_FMT,