[PATCH v2 1/3] serdev: handle devices without an ACPI or device tree node

[ChunAn Wu <an.wu@canonical.com>]

Driver-created serdev clients may lack an ACPI companion or device tree
node.

Add a creator-supplied name for these clients. Use it as a serial
modalias fallback and to match a serdev driver of the same name. Keep
returning -ENODEV for unnamed clients.

Signed-off-by: ChunAn Wu <an.wu@canonical.com>
---
 drivers/tty/serdev/core.c | 36 ++++++++++++++++++++++++++++++------
 include/linux/serdev.h    | 31 +++++++++++++++++++++++++++++++
 2 files changed, 61 insertions(+), 6 deletions(-)

diff --git a/drivers/tty/serdev/core.c b/drivers/tty/serdev/core.c
index 7500efcdfc21..8354a4688fd8 100644
--- a/drivers/tty/serdev/core.c
+++ b/drivers/tty/serdev/core.c
@@ -29,13 +29,21 @@ static DEFINE_IDA(ctrl_ida);
 static ssize_t modalias_show(struct device *dev,
 			     struct device_attribute *attr, char *buf)
 {
+	const struct serdev_device *serdev = to_serdev_device(dev);
 	int len;
 
 	len = acpi_device_modalias(dev, buf, PAGE_SIZE - 1);
 	if (len != -ENODEV)
 		return len;
 
-	return of_device_modalias(dev, buf, PAGE_SIZE);
+	len = of_device_modalias(dev, buf, PAGE_SIZE);
+	if (len != -ENODEV)
+		return len;
+
+	if (!serdev->name[0])
+		return -ENODEV;
+
+	return sysfs_emit(buf, "%s%s\n", SERDEV_MODULE_PREFIX, serdev->name);
 }
 static DEVICE_ATTR_RO(modalias);
 
@@ -47,15 +55,22 @@ ATTRIBUTE_GROUPS(serdev_device);
 
 static int serdev_device_uevent(const struct device *dev, struct kobj_uevent_env *env)
 {
+	const struct serdev_device *serdev = to_serdev_device(dev);
 	int rc;
 
-	/* TODO: platform modalias */
-
 	rc = acpi_device_uevent_modalias(dev, env);
 	if (rc != -ENODEV)
 		return rc;
 
-	return of_device_uevent_modalias(dev, env);
+	rc = of_device_uevent_modalias(dev, env);
+	if (rc != -ENODEV)
+		return rc;
+
+	if (!serdev->name[0])
+		return -ENODEV;
+
+	add_uevent_var(env, "MODALIAS=%s%s", SERDEV_MODULE_PREFIX, serdev->name);
+	return 0;
 }
 
 static void serdev_device_release(struct device *dev)
@@ -88,14 +103,23 @@ static const struct device_type serdev_ctrl_type = {
 
 static int serdev_device_match(struct device *dev, const struct device_driver *drv)
 {
+	const struct serdev_device *serdev;
+
 	if (!is_serdev_device(dev))
 		return 0;
 
-	/* TODO: platform matching */
 	if (acpi_driver_match_device(dev, drv))
 		return 1;
 
-	return of_driver_match_device(dev, drv);
+	if (of_driver_match_device(dev, drv))
+		return 1;
+
+	/* Fall back to the name set by the creator of the device */
+	serdev = to_serdev_device(dev);
+	if (!serdev->name[0])
+		return 0;
+
+	return strcmp(serdev->name, drv->name) == 0;
 }
 
 /**
diff --git a/include/linux/serdev.h b/include/linux/serdev.h
index b6c3d957ec15..26baa0321eef 100644
--- a/include/linux/serdev.h
+++ b/include/linux/serdev.h
@@ -8,6 +8,7 @@
 #include <linux/types.h>
 #include <linux/device.h>
 #include <linux/iopoll.h>
+#include <linux/string.h>
 #include <linux/uaccess.h>
 #include <linux/termios.h>
 #include <linux/delay.h>
@@ -19,6 +20,10 @@ struct serdev_device;
  * serdev device structures
  */
 
+/* Large enough to hold the KBUILD_MODNAME of any serdev client driver */
+#define SERDEV_NAME_SIZE	40
+#define SERDEV_MODULE_PREFIX	"serial:"
+
 /**
  * struct serdev_device_ops - Callback operations for a serdev device
  * @receive_buf:	Function called with data received from device;
@@ -35,6 +40,9 @@ struct serdev_device_ops {
  * struct serdev_device - Basic representation of an serdev device
  * @dev:	Driver model representation of the device.
  * @nr:		Device number on serdev bus.
+ * @name:	Name of the device, set by its creator, empty for devices
+ *		which are enumerated from firmware, see
+ *		serdev_device_set_name().
  * @ctrl:	serdev controller managing this device.
  * @ops:	Device operations.
  * @write_comp:	Completion used by serdev_device_write() internally
@@ -43,6 +51,7 @@ struct serdev_device_ops {
 struct serdev_device {
 	struct device dev;
 	int nr;
+	char name[SERDEV_NAME_SIZE];
 	struct serdev_controller *ctrl;
 	const struct serdev_device_ops *ops;
 	struct completion write_comp;
@@ -135,6 +144,28 @@ static inline void serdev_device_set_client_ops(struct serdev_device *serdev,
 	serdev->ops = ops;
 }
 
+/**
+ * serdev_device_set_name() - set the name of a serdev device
+ * @serdev:	serdev device.
+ * @name:	non-empty name to use, typically KBUILD_MODNAME of the client
+ *		driver.
+ *
+ * A serdev device is identified by its ACPI companion, by its device tree
+ * node, or by a name set by its creator. Serdev devices which are
+ * instantiated by a driver rather than by firmware have neither of the
+ * former, so they must set a name before serdev_device_add() to be
+ * identifiable. Doing so gives them a SERDEV_MODULE_PREFIX modalias and
+ * makes them match a serdev device driver of the same name.
+ *
+ * Devices enumerated from firmware have no name and keep deriving their
+ * modalias and their driver match from firmware only.
+ */
+static inline void serdev_device_set_name(struct serdev_device *serdev,
+					  const char *name)
+{
+	strscpy(serdev->name, name);
+}
+
 static inline
 void *serdev_controller_get_drvdata(const struct serdev_controller *ctrl)
 {

base-commit: 9e947d96915af63e28896caae85a81b74855621b
-- 
2.34.1