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

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

[ChunAn Wu]

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

[PATCH v2 2/3] platform/x86: dell-uart-backlight: Bind through normal serdev matching

[ChunAn Wu]

The driver creates a serdev client without firmware metadata and
force-attaches its driver.

Set its name before adding it so the serdev core can match the driver
normally, then remove the manual attachment.

Signed-off-by: ChunAn Wu <an.wu@canonical.com>
---
 drivers/platform/x86/dell/dell-uart-backlight.c | 12 ++----------
 1 file changed, 2 insertions(+), 10 deletions(-)

diff --git a/drivers/platform/x86/dell/dell-uart-backlight.c b/drivers/platform/x86/dell/dell-uart-backlight.c
index f323a667dc2d..19ed7f8b12bd 100644
--- a/drivers/platform/x86/dell/dell-uart-backlight.c
+++ b/drivers/platform/x86/dell/dell-uart-backlight.c
@@ -354,6 +354,8 @@ static int dell_uart_bl_pdev_probe(struct platform_device *pdev)
 	if (!serdev)
 		return -ENOMEM;
 
+	serdev_device_set_name(serdev, KBUILD_MODNAME);
+
 	ret = serdev_device_add(serdev);
 	if (ret) {
 		dev_err(&pdev->dev, "error %d adding serdev\n", ret);
@@ -365,20 +367,10 @@ static int dell_uart_bl_pdev_probe(struct platform_device *pdev)
 	if (ret)
 		goto err_remove_serdev;
 
-	/*
-	 * serdev device <-> driver matching relies on OF or ACPI matches and
-	 * neither is available here, manually bind the driver.
-	 */
-	ret = device_driver_attach(&dell_uart_bl_serdev_driver.driver, &serdev->dev);
-	if (ret)
-		goto err_unregister_serdev_driver;
-
 	/* So that dell_uart_bl_pdev_remove() can remove the serdev */
 	platform_set_drvdata(pdev, serdev);
 	return 0;
 
-err_unregister_serdev_driver:
-	serdev_device_driver_unregister(&dell_uart_bl_serdev_driver);
 err_remove_serdev:
 	serdev_device_remove(serdev);
 	return ret;
-- 
2.34.1

[PATCH v2 3/3] platform/x86: lenovo-yoga-tab2-pro-1380-fastcharger: Bind through normal serdev matching

[ChunAn Wu]

The software-node-backed serdev client cannot match through ACPI or
device tree and is force-attached.

Set its name before adding it so the serdev core matches it normally.
Deferred probing is then handled by the driver core.

Signed-off-by: ChunAn Wu <an.wu@canonical.com>
---
 .../lenovo/yoga-tab2-pro-1380-fastcharger.c   | 21 ++++++-------------
 1 file changed, 6 insertions(+), 15 deletions(-)

diff --git a/drivers/platform/x86/lenovo/yoga-tab2-pro-1380-fastcharger.c b/drivers/platform/x86/lenovo/yoga-tab2-pro-1380-fastcharger.c
index 8551ab4d2c7d..2eee9ecbcae7 100644
--- a/drivers/platform/x86/lenovo/yoga-tab2-pro-1380-fastcharger.c
+++ b/drivers/platform/x86/lenovo/yoga-tab2-pro-1380-fastcharger.c
@@ -260,25 +260,14 @@ static int yt2_1380_fc_pdev_probe(struct platform_device *pdev)
 	/* The fwnode is a managed node, so it will be auto-put on serdev_device_put() */
 	fwnode_handle_get(dev_fwnode(&serdev->dev));
 
+	serdev_device_set_name(serdev, KBUILD_MODNAME);
+
 	ret = serdev_device_add(serdev);
 	if (ret) {
 		serdev_device_put(serdev);
 		return dev_err_probe(&pdev->dev, ret, "adding serdev\n");
 	}
 
-	/*
-	 * serdev device <-> driver matching relies on OF or ACPI matches and
-	 * neither is available here, manually bind the driver.
-	 */
-	ret = device_driver_attach(&yt2_1380_fc_serdev_driver.driver, &serdev->dev);
-	if (ret) {
-		/* device_driver_attach() maps EPROBE_DEFER to EAGAIN, map it back */
-		serdev_device_remove(serdev);
-		return dev_err_probe(&pdev->dev,
-				     (ret == -EAGAIN) ? -EPROBE_DEFER : ret,
-				     "attaching serdev driver\n");
-	}
-
 	/* So that yt2_1380_fc_pdev_remove() can remove the serdev */
 	platform_set_drvdata(pdev, serdev);
 	return 0;
@@ -305,8 +294,10 @@ static int __init yt2_1380_fc_module_init(void)
 	int ret;
 
 	/*
-	 * serdev driver MUST be registered first because pdev driver calls
-	 * device_driver_attach() on the serdev, serdev-driver pair.
+	 * Register the serdev driver first, so that the serdev device added
+	 * by the pdev driver's probe() matches it and gets probed. serdev
+	 * drivers are probed asynchronously, so that probe may still be
+	 * running when the pdev probe() returns.
 	 */
 	ret = serdev_device_driver_register(&yt2_1380_fc_serdev_driver);
 	if (ret)
-- 
2.34.1

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

[Markus Probst]

[-- Attachment #1: Type: text/plain, Size: 6517 bytes --]

On Wed, 2026-10-21 at 17:21 +0800, ChunAn Wu wrote:
> 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:"
Move into include/linux/device-id/, see below first.

> +
>  /**
>   * 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);
> +}
> +
If you set a name via `serdev_device_set_name()`, the actual device
name will still be "serial0-0" or similar.

I don't think we should change the actual device name though, as it is
a potentially breaking change.

Instead we should name the field "modalias" like in the spi bus. So its
clear it doesn't represent the device name.


Also add

`const struct serdev_device_id *id_table;`

to `struct serdev_device_driver`.
This makes it more consistent with other bus devices. It makes it also
possible to handle multiple serial devices (without fwnode), including
storing different private data.

You will have to define serdev_device_id first inside
`include/linux/device-id/`.

Thanks
- Markus Probst


>  static inline
>  void *serdev_controller_get_drvdata(const struct serdev_controller *ctrl)
>  {
> 
> base-commit: 9e947d96915af63e28896caae85a81b74855621b

[-- Attachment #2: This is a digitally signed message part --]
[-- Type: application/pgp-signature, Size: 870 bytes --]

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

[Hans de Goede]

Hi,

On 21-Oct-26 11:21, ChunAn Wu wrote:
> 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>

For v3 of this series please include a cover-letter and explain
why this series is an improvement over the` existing situation.

The dell-uart-backlight and lenovo-yoga-tab2-pro-1380-fastcharger
drivers are both pretty special cases and here you are adding
a chunk of code to the serdev-core for those special cases,
so I wonder: why?

The current manual attach approach taking in these 2 special
drivers works fine.

What does this new approach gain us ?

Also if you are going to do this may I suggest looking at doing
some sort of of-compatible matching based on a compatible string
inside a swnode ? I do not know what that would look like but
that is something which seems like it might be generally useful
also outside these 2 special cases.

Regards,

Hans



> ---
>  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

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

[Markus Probst]

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On Wed, 2026-10-21 at 16:32 +0200, Hans de Goede wrote:
> Hi,
> 
> On 21-Oct-26 11:21, ChunAn Wu wrote:
> > 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>
> 
> For v3 of this series please include a cover-letter and explain
> why this series is an improvement over the` existing situation.
> 
> The dell-uart-backlight and lenovo-yoga-tab2-pro-1380-fastcharger
> drivers are both pretty special cases and here you are adding
> a chunk of code to the serdev-core for those special cases,
> so I wonder: why?
> 
> The current manual attach approach taking in these 2 special
> drivers works fine.
> 
> What does this new approach gain us ?

That was my review comment [1] that resulted in this.

From what I can tell from revision 1, ChunAn Wu is trying to fix that
accessing uevent and modalias of the device (via sysfs) results in a -
ENODEV error.

As mentioned in my review:

- "/* TODO: platform modalias */"
- "/* TODO: platform matching */"
still exist in the serdev codebase (drivers/tty/serdev/core.c) and are
unresolved. Resolving those also fixes the issue mentioned above.
Therefore I think this would be a better approach.

A cover letter is ofc still needed.

> 
> Also if you are going to do this may I suggest looking at doing
> some sort of of-compatible matching based on a compatible string
> inside a swnode ? I do not know what that would look like but
> that is something which seems like it might be generally useful
> also outside these 2 special cases.

I haven't used them before, but I don't think of-compatible string
matching inside a swnode is done anywhere in the kernel (At least I
haven't found a case).

They can be added supplementary if needed.

Thanks
- Markus Probst

[1]
https://lore.kernel.org/linux-serial/8e4ca13d3e8acd5d649bd4c7357e5da0785ba6b3.camel@posteo.de/

> 
> Regards,
> 
> Hans
> 
> 
> 
> > ---
> >  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

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

[Hans de Goede]

Hi,

On 21-Oct-26 17:08, Markus Probst wrote:
> On Wed, 2026-10-21 at 16:32 +0200, Hans de Goede wrote:
>> Hi,
>>
>> On 21-Oct-26 11:21, ChunAn Wu wrote:
>>> 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>
>>
>> For v3 of this series please include a cover-letter and explain
>> why this series is an improvement over the` existing situation.
>>
>> The dell-uart-backlight and lenovo-yoga-tab2-pro-1380-fastcharger
>> drivers are both pretty special cases and here you are adding
>> a chunk of code to the serdev-core for those special cases,
>> so I wonder: why?
>>
>> The current manual attach approach taking in these 2 special
>> drivers works fine.
>>
>> What does this new approach gain us ?
> 
> That was my review comment [1] that resulted in this.

Thanks, that is useful info and the kinda info I would
expect in a cover-letter :)
> From what I can tell from revision 1, ChunAn Wu is trying to fix that
> accessing uevent and modalias of the device (via sysfs) results in a -
> ENODEV error.

I see. Makes me wonder though how that -ENODEV is a problem,
it is weird. But is it a problem?

The v1 patch writes the following about this:

"This makes the modalias sysfs read fail and suppresses the device
add uevent, even though the device is registered and bound to its driver."

Ok, but the backlight driver ultimately ends up adding a
/sys/class/backlight device which I assume does get
a uevent, or is the problem that one never getting a uevent
because of its parent not getting one ?

And the lenovo-yoga-tab2-pro-1380-fastcharger driver does all
it needs to do fully in kernel and does not even export
a userspace interface.

> As mentioned in my review:
> 
> - "/* TODO: platform modalias */"
> - "/* TODO: platform matching */"
> still exist in the serdev codebase (drivers/tty/serdev/core.c) and are
> unresolved. Resolving those also fixes the issue mentioned above.
> Therefore I think this would be a better approach.

With that said given that there are TODO comments for this
I guess addressing the TODO-s is ok.
> A cover letter is ofc still needed.

Ack.

>> Also if you are going to do this may I suggest looking at doing
>> some sort of of-compatible matching based on a compatible string
>> inside a swnode ? I do not know what that would look like but
>> that is something which seems like it might be generally useful
>> also outside these 2 special cases.
> 
> I haven't used them before, but I don't think of-compatible string
> matching inside a swnode is done anywhere in the kernel (At least I
> haven't found a case).
> 
> They can be added supplementary if needed.

The idea was to make this a generic match mechanism / helper
function busses can call, like the current of and acpi
match (and modalias) helpers. And then have matching by
a compatible string instead of by name since matching by name
only works if there is only 1 instance.

Anyways this is just an idea and somewhat out of scope for
this patch-set.

Regards,

Hans

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

[Markus Probst]

[-- Attachment #1: Type: text/plain, Size: 4343 bytes --]

On Wed, 2026-10-21 at 20:07 +0200, Hans de Goede wrote:
> Hi,
> 
> On 21-Oct-26 17:08, Markus Probst wrote:
> > On Wed, 2026-10-21 at 16:32 +0200, Hans de Goede wrote:
> > > Hi,
> > > 
> > > On 21-Oct-26 11:21, ChunAn Wu wrote:
> > > > 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>
> > > 
> > > For v3 of this series please include a cover-letter and explain
> > > why this series is an improvement over the` existing situation.
> > > 
> > > The dell-uart-backlight and lenovo-yoga-tab2-pro-1380-fastcharger
> > > drivers are both pretty special cases and here you are adding
> > > a chunk of code to the serdev-core for those special cases,
> > > so I wonder: why?
> > > 
> > > The current manual attach approach taking in these 2 special
> > > drivers works fine.
> > > 
> > > What does this new approach gain us ?
> > 
> > That was my review comment [1] that resulted in this.
> 
> Thanks, that is useful info and the kinda info I would
> expect in a cover-letter :)
> > From what I can tell from revision 1, ChunAn Wu is trying to fix that
> > accessing uevent and modalias of the device (via sysfs) results in a -
> > ENODEV error.
> 
> I see. Makes me wonder though how that -ENODEV is a problem,
> it is weird. But is it a problem?
> 
> The v1 patch writes the following about this:
> 
> "This makes the modalias sysfs read fail and suppresses the device
> add uevent, even though the device is registered and bound to its driver."
> 
> Ok, but the backlight driver ultimately ends up adding a
> /sys/class/backlight device which I assume does get
> a uevent, or is the problem that one never getting a uevent
> because of its parent not getting one ?
> 
> And the lenovo-yoga-tab2-pro-1380-fastcharger driver does all
> it needs to do fully in kernel and does not even export
> a userspace interface.
I am not sure which issue is solves precisely. Maybe udev doesn't like
it?

ChunAn Wu has to answer that.

Returning -ENODEV on an existing device there is likely not intended.


> 
> > As mentioned in my review:
> > 
> > - "/* TODO: platform modalias */"
> > - "/* TODO: platform matching */"
> > still exist in the serdev codebase (drivers/tty/serdev/core.c) and are
> > unresolved. Resolving those also fixes the issue mentioned above.
> > Therefore I think this would be a better approach.
> 
> With that said given that there are TODO comments for this
> I guess addressing the TODO-s is ok.
> > A cover letter is ofc still needed.
> 
> Ack.
> 
> > > Also if you are going to do this may I suggest looking at doing
> > > some sort of of-compatible matching based on a compatible string
> > > inside a swnode ? I do not know what that would look like but
> > > that is something which seems like it might be generally useful
> > > also outside these 2 special cases.
> > 
> > I haven't used them before, but I don't think of-compatible string
> > matching inside a swnode is done anywhere in the kernel (At least I
> > haven't found a case).
> > 
> > They can be added supplementary if needed.
> 
> The idea was to make this a generic match mechanism / helper
> function busses can call, like the current of and acpi
> match (and modalias) helpers. And then have matching by
> a compatible string instead of by name since matching by name
> only works if there is only 1 instance.
Please take a look at my previous review comment [1].

In this I suggested adding a `id_table` field to `serdev_driver`.
This allows to match multiple instances, including providing different
private datas.

software node is only relevant I think if you already use
`fwnode_property_read_string` inside a driver next to acpi and of, and
also want to handle devices without of or acpi.

Thanks
- Markus Probst

[1]
https://lore.kernel.org/linux-serial/0be5624e3778c3426f88daf2d67376435f474497.camel@posteo.de/

> 
> Anyways this is just an idea and somewhat out of scope for
> this patch-set.
> 
> Regards,
> 
> Hans
> 

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