[PATCH v4 0/3] serdev: handle devices without an ACPI or device tree node

[PATCH v4 0/3] serdev: handle devices without an ACPI or device tree node

[ChunAn Wu]

Driver-created serdev clients without an ACPI companion or device tree
node currently have no modalias and cannot be matched to a driver:
their modalias sysfs read returns -ENODEV and their creators force a
bind with device_driver_attach().

Backlight function on dell-uart-backlight is not affected: that class
device is registered independently and gets its own add uevent. The
user-visible breakage is the failing modalias read on an existing
serdev child -- Checkbox dkms_info_attachment aborts with
"OSError: [Errno 19] No such device".

Resolve the two long-standing serdev-core TODOs by letting the creator
pass a modalias to serdev_device_add() and giving the serdev driver an
id_table, modelled on the SPI bus. ACPI and OF match first and are
unchanged. Convert dell-uart-backlight and the Lenovo Yoga Tab 2 Pro
fastcharger to this path and drop their force-attach workarounds.

Changes in v4:
- Patch 1: drop the dead is_serdev_device() guard from the match
  callback, and dereference serdev once at the top
- Patch 1: drop the "large enough" comment on SERDEV_NAME_SIZE
- Patch 1: in struct serdev_device_driver, place id_table right under
  driver, next to driver->of_match_table and driver->acpi_match_table
- Patch 1: merge serdev_device_set_modalias() into serdev_device_add()
  so the modalias is set at the only point where forgetting it would
  matter; internal firmware callers pass NULL
- All three patches: tightened commit messages and moved the v2/v3
  changelog narrative out of Patch 1 into this cover letter

Changes in v3:
- Rename struct serdev_device::name to ::modalias; dev_name() is
  unchanged
- Model matching on the SPI bus: add struct serdev_device_id and
  id_table; drop driver->name matching
- Add serdev_device_set_modalias() helper and SERDEV_MODULE_PREFIX
- No MODULE_DEVICE_TABLE(serdev, ...) support: both in-tree
  firmware-less clients are created by the same module that provides
  their driver, so udev has nothing to autoload

Changes in v2:
- Instead of silently returning success with no modalias, use a
  creator-supplied name as a "serial:<name>" modalias fallback and as
  the matching key, so clients can bind through normal serdev matching

v3: https://lore.kernel.org/lkml/20261023052717.2577234-1-an.wu@canonical.com/
v2: https://lore.kernel.org/lkml/20261022032842.2492572-1-an.wu@canonical.com/
v1: https://lore.kernel.org/lkml/20261021092124.2306053-1-an.wu@canonical.com/

ChunAn Wu (3):
  serdev: handle devices without an ACPI or device tree node
  platform/x86: dell-uart-backlight: Bind through normal serdev matching
  platform/x86: lenovo-yoga-tab2-pro-1380-fastcharger: Bind through
    normal serdev matching

 MAINTAINERS                                   |  1 +
 .../platform/x86/dell/dell-uart-backlight.c   | 33 ++++------
 .../lenovo/yoga-tab2-pro-1380-fastcharger.c   | 25 +++----
 .../platform/x86/x86-android-tablets/core.c   |  2 +-
 drivers/power/sequencing/pwrseq-pcie-m2.c     |  2 +-
 drivers/tty/serdev/core.c                     | 65 ++++++++++++++-----
 include/linux/device-id/serdev.h              | 19 ++++++
 include/linux/serdev.h                        | 12 +++-
 8 files changed, 105 insertions(+), 54 deletions(-)
 create mode 100644 include/linux/device-id/serdev.h


base-commit: 9e947d96915af63e28896caae85a81b74855621b
--
2.34.1

[PATCH v4 1/3] serdev: handle devices without an ACPI or device tree node

[ChunAn Wu]

Serdev clients instantiated by a driver have no ACPI companion and no
device tree node. Their modalias read returns -ENODEV, their add uevent
is suppressed, and they cannot be driver-matched, so creators force a
bind with device_driver_attach().

Resolve both TODOs in the serdev core by modelling matching on the SPI
bus: let the creator pass a modalias to serdev_device_add() and give
struct serdev_device_driver an id_table. ACPI and OF are still tried
first; clients without their own modalias keep returning -ENODEV. The
device name, derived from the controller, is unchanged.

Split struct serdev_device_id and its defines into a new
include/linux/device-id/serdev.h, following the pattern already used by
the SPI and I2C buses.

Signed-off-by: ChunAn Wu <an.wu@canonical.com>
---
 MAINTAINERS                                   |  1 +
 .../platform/x86/x86-android-tablets/core.c   |  2 +-
 drivers/power/sequencing/pwrseq-pcie-m2.c     |  2 +-
 drivers/tty/serdev/core.c                     | 65 ++++++++++++++-----
 include/linux/device-id/serdev.h              | 19 ++++++
 include/linux/serdev.h                        | 12 +++-
 6 files changed, 82 insertions(+), 19 deletions(-)
 create mode 100644 include/linux/device-id/serdev.h

diff --git a/MAINTAINERS b/MAINTAINERS
index 917f3f72e31b..06e67aa5d9b0 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -24905,6 +24905,7 @@ L:	linux-serial@vger.kernel.org
 S:	Maintained
 F:	Documentation/devicetree/bindings/serial/serial.yaml
 F:	drivers/tty/serdev/
+F:	include/linux/device-id/serdev.h
 F:	include/linux/serdev.h
 F:	rust/helpers/serdev.c
 F:	rust/kernel/serdev.rs
diff --git a/drivers/platform/x86/x86-android-tablets/core.c b/drivers/platform/x86/x86-android-tablets/core.c
index cfff7f5eac5d..853aa6ff5d50 100644
--- a/drivers/platform/x86/x86-android-tablets/core.c
+++ b/drivers/platform/x86/x86-android-tablets/core.c
@@ -317,7 +317,7 @@ static __init int x86_instantiate_serdev(const struct x86_dev_info *dev_info, in
 	ACPI_COMPANION_SET(&serdev->dev, serdev_adev);
 	acpi_device_set_enumerated(serdev_adev);
 
-	ret = serdev_device_add(serdev);
+	ret = serdev_device_add(serdev, NULL);
 	if (ret) {
 		dev_err(&serdev->dev, "error %d adding serdev\n", ret);
 		serdev_device_put(serdev);
diff --git a/drivers/power/sequencing/pwrseq-pcie-m2.c b/drivers/power/sequencing/pwrseq-pcie-m2.c
index e42e85f47629..e0482f2ef39f 100644
--- a/drivers/power/sequencing/pwrseq-pcie-m2.c
+++ b/drivers/power/sequencing/pwrseq-pcie-m2.c
@@ -309,7 +309,7 @@ static int pwrseq_pcie_m2_create_serdev_one(struct pwrseq_pcie_m2_ctx *ctx,
 	if (ret)
 		goto err_free_serdev;
 
-	ret = serdev_device_add(pci_dev->serdev);
+	ret = serdev_device_add(pci_dev->serdev, NULL);
 	if (ret) {
 		dev_err(dev, "Failed to add serdev for PCI device (%s): %d\n",
 			pci_name(pdev), ret);
diff --git a/drivers/tty/serdev/core.c b/drivers/tty/serdev/core.c
index 7500efcdfc21..45175403bd55 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->modalias[0])
+		return -ENODEV;
+
+	return sysfs_emit(buf, "%s%s\n", SERDEV_MODULE_PREFIX, serdev->modalias);
 }
 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->modalias[0])
+		return -ENODEV;
+
+	return add_uevent_var(env, "MODALIAS=%s%s", SERDEV_MODULE_PREFIX,
+			      serdev->modalias);
 }
 
 static void serdev_device_release(struct device *dev)
@@ -70,11 +85,6 @@ static const struct device_type serdev_device_type = {
 	.release	= serdev_device_release,
 };
 
-static bool is_serdev_device(const struct device *dev)
-{
-	return dev->type == &serdev_device_type;
-}
-
 static void serdev_ctrl_release(struct device *dev)
 {
 	struct serdev_controller *ctrl = to_serdev_controller(dev);
@@ -86,28 +96,51 @@ static const struct device_type serdev_ctrl_type = {
 	.release	= serdev_ctrl_release,
 };
 
+static const struct serdev_device_id *serdev_match_id(const struct serdev_device_id *id,
+						      const char *modalias)
+{
+	if (!id || !modalias[0])
+		return NULL;
+
+	while (id->name[0]) {
+		if (!strcmp(modalias, id->name))
+			return id;
+		id++;
+	}
+
+	return NULL;
+}
+
 static int serdev_device_match(struct device *dev, const struct device_driver *drv)
 {
-	if (!is_serdev_device(dev))
-		return 0;
+	const struct serdev_device *serdev = to_serdev_device(dev);
+	const struct serdev_device_driver *sdrv = to_serdev_device_driver(drv);
 
-	/* 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;
+
+	return !!serdev_match_id(sdrv->id_table, serdev->modalias);
 }
 
 /**
  * serdev_device_add() - add a device previously constructed via serdev_device_alloc()
  * @serdev:	serdev_device to be added
+ * @modalias:	Driver name or alias, used to match devices which have neither
+ *		an ACPI companion nor a device tree node. NULL for devices
+ *		enumerated from firmware.
  */
-int serdev_device_add(struct serdev_device *serdev)
+int serdev_device_add(struct serdev_device *serdev, const char *modalias)
 {
 	struct serdev_controller *ctrl = serdev->ctrl;
 	struct device *parent = serdev->dev.parent;
 	int err;
 
+	if (modalias)
+		strscpy(serdev->modalias, modalias);
+
 	dev_set_name(&serdev->dev, "%s-%d", dev_name(parent), serdev->nr);
 
 	/* Only a single slave device is currently supported. */
@@ -553,7 +586,7 @@ static int of_serdev_register_devices(struct serdev_controller *ctrl)
 
 		device_set_node(&serdev->dev, of_fwnode_handle(node));
 
-		err = serdev_device_add(serdev);
+		err = serdev_device_add(serdev, NULL);
 		if (err) {
 			dev_err(&serdev->dev,
 				"failure adding device. status %pe\n",
@@ -707,7 +740,7 @@ static acpi_status acpi_serdev_register_device(struct serdev_controller *ctrl,
 	ACPI_COMPANION_SET(&serdev->dev, adev);
 	acpi_device_set_enumerated(adev);
 
-	err = serdev_device_add(serdev);
+	err = serdev_device_add(serdev, NULL);
 	if (err) {
 		dev_err(&serdev->dev,
 			"failure adding ACPI serdev device. status %pe\n",
diff --git a/include/linux/device-id/serdev.h b/include/linux/device-id/serdev.h
new file mode 100644
index 000000000000..96644953cece
--- /dev/null
+++ b/include/linux/device-id/serdev.h
@@ -0,0 +1,19 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef LINUX_DEVICE_ID_SERDEV_H
+#define LINUX_DEVICE_ID_SERDEV_H
+
+#ifdef __KERNEL__
+typedef unsigned long kernel_ulong_t;
+#endif
+
+/* serdev */
+
+#define SERDEV_NAME_SIZE	40
+#define SERDEV_MODULE_PREFIX	"serial:"
+
+struct serdev_device_id {
+	char name[SERDEV_NAME_SIZE];
+	kernel_ulong_t driver_data;	/* Data private to the driver */
+};
+
+#endif /* ifndef LINUX_DEVICE_ID_SERDEV_H */
diff --git a/include/linux/serdev.h b/include/linux/serdev.h
index b6c3d957ec15..96a441abc1ac 100644
--- a/include/linux/serdev.h
+++ b/include/linux/serdev.h
@@ -7,7 +7,9 @@
 
 #include <linux/types.h>
 #include <linux/device.h>
+#include <linux/device-id/serdev.h>
 #include <linux/iopoll.h>
+#include <linux/string.h>
 #include <linux/uaccess.h>
 #include <linux/termios.h>
 #include <linux/delay.h>
@@ -35,6 +37,10 @@ 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.
+ * @modalias:	Name of the driver to use with this device, or the alias
+ *		for it. Empty for devices enumerated from firmware, which
+ *		are identified through their ACPI companion or their device
+ *		tree node instead. See serdev_device_add().
  * @ctrl:	serdev controller managing this device.
  * @ops:	Device operations.
  * @write_comp:	Completion used by serdev_device_write() internally
@@ -43,6 +49,7 @@ struct serdev_device_ops {
 struct serdev_device {
 	struct device dev;
 	int nr;
+	char modalias[SERDEV_NAME_SIZE];
 	struct serdev_controller *ctrl;
 	const struct serdev_device_ops *ops;
 	struct completion write_comp;
@@ -55,12 +62,15 @@ struct serdev_device {
  * struct serdev_device_driver - serdev slave device driver
  * @driver:	serdev device drivers should initialize name field of this
  *		structure.
+ * @id_table:	List of serdev devices supported by this driver, used to
+ *		match devices which are not enumerated from firmware.
  * @probe:	binds this driver to a serdev device.
  * @remove:	unbinds this driver from the serdev device.
  * @shutdown:	shut down this serdev device.
  */
 struct serdev_device_driver {
 	struct device_driver driver;
+	const struct serdev_device_id *id_table;
 	int	(*probe)(struct serdev_device *);
 	void	(*remove)(struct serdev_device *);
 	void	(*shutdown)(struct serdev_device *);
@@ -158,7 +168,7 @@ static inline void serdev_controller_put(struct serdev_controller *ctrl)
 }
 
 struct serdev_device *serdev_device_alloc(struct serdev_controller *);
-int serdev_device_add(struct serdev_device *);
+int serdev_device_add(struct serdev_device *serdev, const char *modalias);
 void serdev_device_remove(struct serdev_device *);
 
 struct serdev_controller *serdev_controller_alloc(struct device *host,
-- 
2.34.1

[PATCH v4] 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 to it.

Pass the modalias to serdev_device_add() and give the serdev driver a
matching id_table, so that the serdev core binds the two through normal
matching, then drop the manual attachment.

The client now also reports a "serial:dell_uart_backlight" modalias to
userspace instead of failing with -ENODEV. A failing serdev probe no
longer propagates out of the platform probe; as for any other bus, the
client is simply left unbound.

Signed-off-by: ChunAn Wu <an.wu@canonical.com>
---
 .../platform/x86/dell/dell-uart-backlight.c    | 18 +++++++-----------
 1 file changed, 7 insertions(+), 11 deletions(-)

diff --git a/drivers/platform/x86/dell/dell-uart-backlight.c b/drivers/platform/x86/dell/dell-uart-backlight.c
index f323a667dc2d..9b8ef91bb0a2 100644
--- a/drivers/platform/x86/dell/dell-uart-backlight.c
+++ b/drivers/platform/x86/dell/dell-uart-backlight.c
@@ -325,11 +325,17 @@ static int dell_uart_bl_serdev_probe(struct serdev_device *serdev)
 	return PTR_ERR_OR_ZERO(dell_bl->bl);
 }
 
+static const struct serdev_device_id dell_uart_bl_serdev_id[] = {
+	{ KBUILD_MODNAME },
+	{ }
+};
+
 static struct serdev_device_driver dell_uart_bl_serdev_driver = {
 	.probe = dell_uart_bl_serdev_probe,
 	.driver = {
 		.name = KBUILD_MODNAME,
 	},
+	.id_table = dell_uart_bl_serdev_id,
 };
 
 static int dell_uart_bl_pdev_probe(struct platform_device *pdev)
@@ -354,7 +360,7 @@ static int dell_uart_bl_pdev_probe(struct platform_device *pdev)
 	if (!serdev)
 		return -ENOMEM;
 
-	ret = serdev_device_add(serdev);
+	ret = serdev_device_add(serdev, KBUILD_MODNAME);
 	if (ret) {
 		dev_err(&pdev->dev, "error %d adding serdev\n", ret);
 		serdev_device_put(serdev);
@@ -365,20 +371,10 @@ 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 v4 3/3] platform/x86: lenovo-yoga-tab2-pro-1380-fastcharger: Bind through normal serdev matching

[ChunAn Wu]

The software-node-backed serdev client cannot be matched through ACPI or
device tree and is force-attached to its driver.

Pass the modalias to serdev_device_add() and give the serdev driver a
matching id_table, so that the serdev core binds the two through normal
matching. Deferred probing is then handled by the driver core, so the
-EAGAIN translation is no longer needed.

A failing serdev probe no longer propagates out of the platform probe;
as for any other bus, the client is simply left unbound.

Signed-off-by: ChunAn Wu <an.wu@canonical.com>
---
 .../lenovo/yoga-tab2-pro-1380-fastcharger.c   | 25 +++++++------------
 1 file changed, 9 insertions(+), 16 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..d0bd9d4e3137 100644
--- a/drivers/platform/x86/lenovo/yoga-tab2-pro-1380-fastcharger.c
+++ b/drivers/platform/x86/lenovo/yoga-tab2-pro-1380-fastcharger.c
@@ -219,11 +219,17 @@ static int yt2_1380_fc_serdev_probe(struct serdev_device *serdev)
 	return 0;
 }
 
+static const struct serdev_device_id yt2_1380_fc_serdev_id[] = {
+	{ KBUILD_MODNAME },
+	{ }
+};
+
 static struct serdev_device_driver yt2_1380_fc_serdev_driver = {
 	.probe = yt2_1380_fc_serdev_probe,
 	.driver = {
 		.name = KBUILD_MODNAME,
 	},
+	.id_table = yt2_1380_fc_serdev_id,
 };
 
 static const struct pinctrl_map yt2_1380_fc_pinctrl_map[] = {
@@ -260,25 +266,12 @@ 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));
 
-	ret = serdev_device_add(serdev);
+	ret = serdev_device_add(serdev, KBUILD_MODNAME);
 	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 +298,8 @@ 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.
+	 * serdev driver MUST be registered first so that the serdev device
+	 * created by the pdev probe binds to it via the id_table match.
 	 */
 	ret = serdev_device_driver_register(&yt2_1380_fc_serdev_driver);
 	if (ret)
-- 
2.34.1

[PATCH v4 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 to it.

Pass the modalias to serdev_device_add() and give the serdev driver a
matching id_table, so that the serdev core binds the two through normal
matching, then drop the manual attachment.

The client now also reports a "serial:dell_uart_backlight" modalias to
userspace instead of failing with -ENODEV. A failing serdev probe no
longer propagates out of the platform probe; as for any other bus, the
client is simply left unbound.

Signed-off-by: ChunAn Wu <an.wu@canonical.com>
---
 .../platform/x86/dell/dell-uart-backlight.c    | 18 +++++++-----------
 1 file changed, 7 insertions(+), 11 deletions(-)

diff --git a/drivers/platform/x86/dell/dell-uart-backlight.c b/drivers/platform/x86/dell/dell-uart-backlight.c
index f323a667dc2d..9b8ef91bb0a2 100644
--- a/drivers/platform/x86/dell/dell-uart-backlight.c
+++ b/drivers/platform/x86/dell/dell-uart-backlight.c
@@ -325,11 +325,17 @@ static int dell_uart_bl_serdev_probe(struct serdev_device *serdev)
 	return PTR_ERR_OR_ZERO(dell_bl->bl);
 }
 
+static const struct serdev_device_id dell_uart_bl_serdev_id[] = {
+	{ KBUILD_MODNAME },
+	{ }
+};
+
 static struct serdev_device_driver dell_uart_bl_serdev_driver = {
 	.probe = dell_uart_bl_serdev_probe,
 	.driver = {
 		.name = KBUILD_MODNAME,
 	},
+	.id_table = dell_uart_bl_serdev_id,
 };
 
 static int dell_uart_bl_pdev_probe(struct platform_device *pdev)
@@ -354,7 +360,7 @@ static int dell_uart_bl_pdev_probe(struct platform_device *pdev)
 	if (!serdev)
 		return -ENOMEM;
 
-	ret = serdev_device_add(serdev);
+	ret = serdev_device_add(serdev, KBUILD_MODNAME);
 	if (ret) {
 		dev_err(&pdev->dev, "error %d adding serdev\n", ret);
 		serdev_device_put(serdev);
@@ -365,20 +371,10 @@ 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

Re: [PATCH v4 0/3] serdev: handle devices without an ACPI or device tree node

[An Wu]

Hi Makus
    According to sashiko:
'''
In drivers/tty/serdev/core.c, serdev_controller_alloc() places controller
devices on serdev_bus_type:

    device_initialize(&ctrl->dev);
    ctrl->dev.type = &serdev_ctrl_type;
    ctrl->dev.bus = &serdev_bus_type;

When yt2_1380_fc_module_init() calls serdev_device_driver_register() for
yt2_1380_fc_serdev_driver (or when a new serdev_controller is added), the
driver core runs serdev_device_match() against every device on
serdev_bus_type, including struct serdev_controller instances:

static int serdev_device_match(struct device *dev, const struct
device_driver *drv)
{
        const struct serdev_device *serdev = to_serdev_device(dev);
        const struct serdev_device_driver *sdrv = to_serdev_device_driver(drv);

        if (acpi_driver_match_device(dev, drv))
                return 1;

        if (of_driver_match_device(dev, drv))
                return 1;

        return !!serdev_match_id(sdrv->id_table, serdev->modalias);
}

Because serdev_device_match() does not check is_serdev_device(dev) before
casting dev with to_serdev_device(dev), and yt2_1380_fc_serdev_driver has no
ACPI or OF match table, serdev_device_match() falls through to
serdev_match_id(sdrv->id_table, serdev->modalias) on struct serdev_controller
devices.

In struct serdev_device, modalias[SERDEV_NAME_SIZE] starts at offset
sizeof(struct device) + 4, which in struct serdev_controller overlaps the
struct device *host pointer, ctrl->nr, ctrl->serdev, ctrl->ops, and extends 12
bytes past sizeof(struct serdev_controller). When the overlapping byte at
modalias[0] is non-zero, serdev_match_id() passes that non-string memory and
trailing out-of-bounds bytes to strcmp().

Should serdev_device_match() verify is_serdev_device(dev) before casting dev
to struct serdev_device?
'''

If we remove is_serdev_device could cause some problem due to the
serdev_controller could also
run into this function and "serdev_match_id(sdrv->id_table,
serdev->modalias);" can be a potential risk.

I will add the "is_serdev_device" back and send v5 out.

BR
    An


On Sat, Oct 24, 2026 at 10:29 AM ChunAn Wu <an.wu@canonical.com> wrote:
>
> Driver-created serdev clients without an ACPI companion or device tree
> node currently have no modalias and cannot be matched to a driver:
> their modalias sysfs read returns -ENODEV and their creators force a
> bind with device_driver_attach().
>
> Backlight function on dell-uart-backlight is not affected: that class
> device is registered independently and gets its own add uevent. The
> user-visible breakage is the failing modalias read on an existing
> serdev child -- Checkbox dkms_info_attachment aborts with
> "OSError: [Errno 19] No such device".
>
> Resolve the two long-standing serdev-core TODOs by letting the creator
> pass a modalias to serdev_device_add() and giving the serdev driver an
> id_table, modelled on the SPI bus. ACPI and OF match first and are
> unchanged. Convert dell-uart-backlight and the Lenovo Yoga Tab 2 Pro
> fastcharger to this path and drop their force-attach workarounds.
>
> Changes in v4:
> - Patch 1: drop the dead is_serdev_device() guard from the match
>   callback, and dereference serdev once at the top
> - Patch 1: drop the "large enough" comment on SERDEV_NAME_SIZE
> - Patch 1: in struct serdev_device_driver, place id_table right under
>   driver, next to driver->of_match_table and driver->acpi_match_table
> - Patch 1: merge serdev_device_set_modalias() into serdev_device_add()
>   so the modalias is set at the only point where forgetting it would
>   matter; internal firmware callers pass NULL
> - All three patches: tightened commit messages and moved the v2/v3
>   changelog narrative out of Patch 1 into this cover letter
>
> Changes in v3:
> - Rename struct serdev_device::name to ::modalias; dev_name() is
>   unchanged
> - Model matching on the SPI bus: add struct serdev_device_id and
>   id_table; drop driver->name matching
> - Add serdev_device_set_modalias() helper and SERDEV_MODULE_PREFIX
> - No MODULE_DEVICE_TABLE(serdev, ...) support: both in-tree
>   firmware-less clients are created by the same module that provides
>   their driver, so udev has nothing to autoload
>
> Changes in v2:
> - Instead of silently returning success with no modalias, use a
>   creator-supplied name as a "serial:<name>" modalias fallback and as
>   the matching key, so clients can bind through normal serdev matching
>
> v3: https://lore.kernel.org/lkml/20261023052717.2577234-1-an.wu@canonical.com/
> v2: https://lore.kernel.org/lkml/20261022032842.2492572-1-an.wu@canonical.com/
> v1: https://lore.kernel.org/lkml/20261021092124.2306053-1-an.wu@canonical.com/
>
> ChunAn Wu (3):
>   serdev: handle devices without an ACPI or device tree node
>   platform/x86: dell-uart-backlight: Bind through normal serdev matching
>   platform/x86: lenovo-yoga-tab2-pro-1380-fastcharger: Bind through
>     normal serdev matching
>
>  MAINTAINERS                                   |  1 +
>  .../platform/x86/dell/dell-uart-backlight.c   | 33 ++++------
>  .../lenovo/yoga-tab2-pro-1380-fastcharger.c   | 25 +++----
>  .../platform/x86/x86-android-tablets/core.c   |  2 +-
>  drivers/power/sequencing/pwrseq-pcie-m2.c     |  2 +-
>  drivers/tty/serdev/core.c                     | 65 ++++++++++++++-----
>  include/linux/device-id/serdev.h              | 19 ++++++
>  include/linux/serdev.h                        | 12 +++-
>  8 files changed, 105 insertions(+), 54 deletions(-)
>  create mode 100644 include/linux/device-id/serdev.h
>
>
> base-commit: 9e947d96915af63e28896caae85a81b74855621b
> --
> 2.34.1
>

Re: [PATCH v4 0/3] serdev: handle devices without an ACPI or device tree node

[Markus Probst]

[-- Attachment #1: Type: text/plain, Size: 6121 bytes --]

On Sat, 2026-10-24 at 16:40 +0800, An Wu wrote:
> Hi Makus
>     According to sashiko:
> '''
> In drivers/tty/serdev/core.c, serdev_controller_alloc() places controller
> devices on serdev_bus_type:
> 
>     device_initialize(&ctrl->dev);
>     ctrl->dev.type = &serdev_ctrl_type;
>     ctrl->dev.bus = &serdev_bus_type;
> 
> When yt2_1380_fc_module_init() calls serdev_device_driver_register() for
> yt2_1380_fc_serdev_driver (or when a new serdev_controller is added), the
> driver core runs serdev_device_match() against every device on
> serdev_bus_type, including struct serdev_controller instances:
> 
> static int serdev_device_match(struct device *dev, const struct
> device_driver *drv)
> {
>         const struct serdev_device *serdev = to_serdev_device(dev);
>         const struct serdev_device_driver *sdrv = to_serdev_device_driver(drv);
> 
>         if (acpi_driver_match_device(dev, drv))
>                 return 1;
> 
>         if (of_driver_match_device(dev, drv))
>                 return 1;
> 
>         return !!serdev_match_id(sdrv->id_table, serdev->modalias);
> }
> 
> Because serdev_device_match() does not check is_serdev_device(dev) before
> casting dev with to_serdev_device(dev), and yt2_1380_fc_serdev_driver has no
> ACPI or OF match table, serdev_device_match() falls through to
> serdev_match_id(sdrv->id_table, serdev->modalias) on struct serdev_controller
> devices.
> 
> In struct serdev_device, modalias[SERDEV_NAME_SIZE] starts at offset
> sizeof(struct device) + 4, which in struct serdev_controller overlaps the
> struct device *host pointer, ctrl->nr, ctrl->serdev, ctrl->ops, and extends 12
> bytes past sizeof(struct serdev_controller). When the overlapping byte at
> modalias[0] is non-zero, serdev_match_id() passes that non-string memory and
> trailing out-of-bounds bytes to strcmp().
> 
> Should serdev_device_match() verify is_serdev_device(dev) before casting dev
> to struct serdev_device?
> '''
> 
> If we remove is_serdev_device could cause some problem due to the
> serdev_controller could also
> run into this function and "serdev_match_id(sdrv->id_table,
> serdev->modalias);" can be a potential risk.
> 
> I will add the "is_serdev_device" back and send v5 out.
Your right, I missed that.

Thanks
- Markus Probst

> 
> BR
>     An
> 
> 
> On Sat, Oct 24, 2026 at 10:29 AM ChunAn Wu <an.wu@canonical.com> wrote:
> > 
> > Driver-created serdev clients without an ACPI companion or device tree
> > node currently have no modalias and cannot be matched to a driver:
> > their modalias sysfs read returns -ENODEV and their creators force a
> > bind with device_driver_attach().
> > 
> > Backlight function on dell-uart-backlight is not affected: that class
> > device is registered independently and gets its own add uevent. The
> > user-visible breakage is the failing modalias read on an existing
> > serdev child -- Checkbox dkms_info_attachment aborts with
> > "OSError: [Errno 19] No such device".
> > 
> > Resolve the two long-standing serdev-core TODOs by letting the creator
> > pass a modalias to serdev_device_add() and giving the serdev driver an
> > id_table, modelled on the SPI bus. ACPI and OF match first and are
> > unchanged. Convert dell-uart-backlight and the Lenovo Yoga Tab 2 Pro
> > fastcharger to this path and drop their force-attach workarounds.
> > 
> > Changes in v4:
> > - Patch 1: drop the dead is_serdev_device() guard from the match
> >   callback, and dereference serdev once at the top
> > - Patch 1: drop the "large enough" comment on SERDEV_NAME_SIZE
> > - Patch 1: in struct serdev_device_driver, place id_table right under
> >   driver, next to driver->of_match_table and driver->acpi_match_table
> > - Patch 1: merge serdev_device_set_modalias() into serdev_device_add()
> >   so the modalias is set at the only point where forgetting it would
> >   matter; internal firmware callers pass NULL
> > - All three patches: tightened commit messages and moved the v2/v3
> >   changelog narrative out of Patch 1 into this cover letter
> > 
> > Changes in v3:
> > - Rename struct serdev_device::name to ::modalias; dev_name() is
> >   unchanged
> > - Model matching on the SPI bus: add struct serdev_device_id and
> >   id_table; drop driver->name matching
> > - Add serdev_device_set_modalias() helper and SERDEV_MODULE_PREFIX
> > - No MODULE_DEVICE_TABLE(serdev, ...) support: both in-tree
> >   firmware-less clients are created by the same module that provides
> >   their driver, so udev has nothing to autoload
> > 
> > Changes in v2:
> > - Instead of silently returning success with no modalias, use a
> >   creator-supplied name as a "serial:<name>" modalias fallback and as
> >   the matching key, so clients can bind through normal serdev matching
> > 
> > v3: https://lore.kernel.org/lkml/20261023052717.2577234-1-an.wu@canonical.com/
> > v2: https://lore.kernel.org/lkml/20261022032842.2492572-1-an.wu@canonical.com/
> > v1: https://lore.kernel.org/lkml/20261021092124.2306053-1-an.wu@canonical.com/
> > 
> > ChunAn Wu (3):
> >   serdev: handle devices without an ACPI or device tree node
> >   platform/x86: dell-uart-backlight: Bind through normal serdev matching
> >   platform/x86: lenovo-yoga-tab2-pro-1380-fastcharger: Bind through
> >     normal serdev matching
> > 
> >  MAINTAINERS                                   |  1 +
> >  .../platform/x86/dell/dell-uart-backlight.c   | 33 ++++------
> >  .../lenovo/yoga-tab2-pro-1380-fastcharger.c   | 25 +++----
> >  .../platform/x86/x86-android-tablets/core.c   |  2 +-
> >  drivers/power/sequencing/pwrseq-pcie-m2.c     |  2 +-
> >  drivers/tty/serdev/core.c                     | 65 ++++++++++++++-----
> >  include/linux/device-id/serdev.h              | 19 ++++++
> >  include/linux/serdev.h                        | 12 +++-
> >  8 files changed, 105 insertions(+), 54 deletions(-)
> >  create mode 100644 include/linux/device-id/serdev.h
> > 
> > 
> > base-commit: 9e947d96915af63e28896caae85a81b74855621b
> > --
> > 2.34.1
> > 

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

Re: [PATCH v4] platform/x86: dell-uart-backlight: Bind through normal serdev matching

[kernel test robot]

Hi ChunAn,

kernel test robot noticed the following build errors:

[auto build test ERROR on driver-core/driver-core-testing]
[also build test ERROR on driver-core/driver-core-next driver-core/driver-core-linus linus/master v7.3 next-20261022]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch#_base_tree_information]

url:    https://github.com/intel-lab-lkp/linux/commits/ChunAn-Wu/platform-x86-dell-uart-backlight-Bind-through-normal-serdev-matching/20261024-102929
base:   driver-core/driver-core-testing
patch link:    https://lore.kernel.org/r/20261024022930.2704030-3-an.wu%40canonical.com
patch subject: [PATCH v4] platform/x86: dell-uart-backlight: Bind through normal serdev matching
config: i386-randconfig-1007-20261024 (https://download.01.org/0day-ci/archive/20261024/202610241920.GJiRENj2-lkp@intel.com/config)
compiler: gcc-14 (Debian 14.2.0-19) 14.2.0
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20261024/202610241920.GJiRENj2-lkp@intel.com/reproduce)

If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@intel.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202610241920.GJiRENj2-lkp@intel.com/

All error/warnings (new ones prefixed by >>):

>> drivers/platform/x86/dell/dell-uart-backlight.c:328:38: error: array type has incomplete element type 'struct serdev_device_id'
     328 | static const struct serdev_device_id dell_uart_bl_serdev_id[] = {
         |                                      ^~~~~~~~~~~~~~~~~~~~~~
>> drivers/platform/x86/dell/dell-uart-backlight.c:338:10: error: 'struct serdev_device_driver' has no member named 'id_table'
     338 |         .id_table = dell_uart_bl_serdev_id,
         |          ^~~~~~~~
   drivers/platform/x86/dell/dell-uart-backlight.c: In function 'dell_uart_bl_pdev_probe':
>> drivers/platform/x86/dell/dell-uart-backlight.c:363:15: error: too many arguments to function 'serdev_device_add'
     363 |         ret = serdev_device_add(serdev, KBUILD_MODNAME);
         |               ^~~~~~~~~~~~~~~~~
   In file included from drivers/platform/x86/dell/dell-uart-backlight.c:19:
   include/linux/serdev.h:161:5: note: declared here
     161 | int serdev_device_add(struct serdev_device *);
         |     ^~~~~~~~~~~~~~~~~
   drivers/platform/x86/dell/dell-uart-backlight.c: At top level:
>> drivers/platform/x86/dell/dell-uart-backlight.c:328:38: warning: 'dell_uart_bl_serdev_id' defined but not used [-Wunused-variable]
     328 | static const struct serdev_device_id dell_uart_bl_serdev_id[] = {
         |                                      ^~~~~~~~~~~~~~~~~~~~~~


vim +328 drivers/platform/x86/dell/dell-uart-backlight.c

   327	
 > 328	static const struct serdev_device_id dell_uart_bl_serdev_id[] = {
   329		{ KBUILD_MODNAME },
   330		{ }
   331	};
   332	
   333	static struct serdev_device_driver dell_uart_bl_serdev_driver = {
   334		.probe = dell_uart_bl_serdev_probe,
   335		.driver = {
   336			.name = KBUILD_MODNAME,
   337		},
 > 338		.id_table = dell_uart_bl_serdev_id,
   339	};
   340	
   341	static int dell_uart_bl_pdev_probe(struct platform_device *pdev)
   342	{
   343		enum acpi_backlight_type bl_type;
   344		struct serdev_device *serdev;
   345		struct device *ctrl_dev;
   346		int ret;
   347	
   348		bl_type = acpi_video_get_backlight_type();
   349		if (bl_type != acpi_backlight_dell_uart) {
   350			dev_dbg(&pdev->dev, "Not loading (ACPI backlight type = %d)\n", bl_type);
   351			return -ENODEV;
   352		}
   353	
   354		ctrl_dev = get_serdev_controller("DELL0501", NULL, 0, "serial0");
   355		if (IS_ERR(ctrl_dev))
   356			return PTR_ERR(ctrl_dev);
   357	
   358		serdev = serdev_device_alloc(to_serdev_controller(ctrl_dev));
   359		put_device(ctrl_dev);
   360		if (!serdev)
   361			return -ENOMEM;
   362	
 > 363		ret = serdev_device_add(serdev, KBUILD_MODNAME);
   364		if (ret) {
   365			dev_err(&pdev->dev, "error %d adding serdev\n", ret);
   366			serdev_device_put(serdev);
   367			return ret;
   368		}
   369	
   370		ret = serdev_device_driver_register(&dell_uart_bl_serdev_driver);
   371		if (ret)
   372			goto err_remove_serdev;
   373	
   374		/* So that dell_uart_bl_pdev_remove() can remove the serdev */
   375		platform_set_drvdata(pdev, serdev);
   376		return 0;
   377	
   378	err_remove_serdev:
   379		serdev_device_remove(serdev);
   380		return ret;
   381	}
   382	

--
0-DAY CI Kernel Test Service
https://github.com/intel/lkp-tests/wiki

Re: [PATCH v4] platform/x86: dell-uart-backlight: Bind through normal serdev matching

[Markus Probst]

[-- Attachment #1: Type: text/plain, Size: 5336 bytes --]

On Sat, 2026-10-24 at 19:59 +0800, kernel test robot wrote:
> Hi ChunAn,
> 
> kernel test robot noticed the following build errors:
> 
> [auto build test ERROR on driver-core/driver-core-testing]
> [also build test ERROR on driver-core/driver-core-next driver-core/driver-core-linus linus/master v7.3 next-20261022]
> [If your patch is applied to the wrong git tree, kindly drop us a note.
> And when submitting patch, we suggest to use '--base' as documented in
> https://git-scm.com/docs/git-format-patch#_base_tree_information]
> 
> url:    https://github.com/intel-lab-lkp/linux/commits/ChunAn-Wu/platform-x86-dell-uart-backlight-Bind-through-normal-serdev-matching/20261024-102929
> base:   driver-core/driver-core-testing
> patch link:    https://lore.kernel.org/r/20261024022930.2704030-3-an.wu%40canonical.com
> patch subject: [PATCH v4] platform/x86: dell-uart-backlight: Bind through normal serdev matching
> config: i386-randconfig-1007-20261024 (https://download.01.org/0day-ci/archive/20261024/202610241920.GJiRENj2-lkp@intel.com/config)
> compiler: gcc-14 (Debian 14.2.0-19) 14.2.0
> reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20261024/202610241920.GJiRENj2-lkp@intel.com/reproduce)
> 
> If you fix the issue in a separate patch/commit (i.e. not just a new version of
> the same patch/commit), kindly add following tags
> > Reported-by: kernel test robot <lkp@intel.com>
> > Closes: https://lore.kernel.org/oe-kbuild-all/202610241920.GJiRENj2-lkp@intel.com/
> 
> All error/warnings (new ones prefixed by >>):
> 
> > > drivers/platform/x86/dell/dell-uart-backlight.c:328:38: error: array type has incomplete element type 'struct serdev_device_id'
>      328 | static const struct serdev_device_id dell_uart_bl_serdev_id[] = {
>          |                                      ^~~~~~~~~~~~~~~~~~~~~~
> > > drivers/platform/x86/dell/dell-uart-backlight.c:338:10: error: 'struct serdev_device_driver' has no member named 'id_table'
>      338 |         .id_table = dell_uart_bl_serdev_id,
>          |          ^~~~~~~~
>    drivers/platform/x86/dell/dell-uart-backlight.c: In function 'dell_uart_bl_pdev_probe':
> > > drivers/platform/x86/dell/dell-uart-backlight.c:363:15: error: too many arguments to function 'serdev_device_add'
>      363 |         ret = serdev_device_add(serdev, KBUILD_MODNAME);
>          |               ^~~~~~~~~~~~~~~~~
>    In file included from drivers/platform/x86/dell/dell-uart-backlight.c:19:
>    include/linux/serdev.h:161:5: note: declared here
>      161 | int serdev_device_add(struct serdev_device *);
>          |     ^~~~~~~~~~~~~~~~~
>    drivers/platform/x86/dell/dell-uart-backlight.c: At top level:
> > > drivers/platform/x86/dell/dell-uart-backlight.c:328:38: warning: 'dell_uart_bl_serdev_id' defined but not used [-Wunused-variable]
>      328 | static const struct serdev_device_id dell_uart_bl_serdev_id[] = {
>          |                                      ^~~~~~~~~~~~~~~~~~~~~~
> 
> 
> vim +328 drivers/platform/x86/dell/dell-uart-backlight.c
> 
>    327	
>  > 328	static const struct serdev_device_id dell_uart_bl_serdev_id[] = {
>    329		{ KBUILD_MODNAME },
>    330		{ }
>    331	};
>    332	
>    333	static struct serdev_device_driver dell_uart_bl_serdev_driver = {
>    334		.probe = dell_uart_bl_serdev_probe,
>    335		.driver = {
>    336			.name = KBUILD_MODNAME,
>    337		},
>  > 338		.id_table = dell_uart_bl_serdev_id,
>    339	};
>    340	
>    341	static int dell_uart_bl_pdev_probe(struct platform_device *pdev)
>    342	{
>    343		enum acpi_backlight_type bl_type;
>    344		struct serdev_device *serdev;
>    345		struct device *ctrl_dev;
>    346		int ret;
>    347	
>    348		bl_type = acpi_video_get_backlight_type();
>    349		if (bl_type != acpi_backlight_dell_uart) {
>    350			dev_dbg(&pdev->dev, "Not loading (ACPI backlight type = %d)\n", bl_type);
>    351			return -ENODEV;
>    352		}
>    353	
>    354		ctrl_dev = get_serdev_controller("DELL0501", NULL, 0, "serial0");
>    355		if (IS_ERR(ctrl_dev))
>    356			return PTR_ERR(ctrl_dev);
>    357	
>    358		serdev = serdev_device_alloc(to_serdev_controller(ctrl_dev));
>    359		put_device(ctrl_dev);
>    360		if (!serdev)
>    361			return -ENOMEM;
>    362	
>  > 363		ret = serdev_device_add(serdev, KBUILD_MODNAME);
>    364		if (ret) {
>    365			dev_err(&pdev->dev, "error %d adding serdev\n", ret);
>    366			serdev_device_put(serdev);
>    367			return ret;
>    368		}
>    369	
>    370		ret = serdev_device_driver_register(&dell_uart_bl_serdev_driver);
>    371		if (ret)
>    372			goto err_remove_serdev;
>    373	
>    374		/* So that dell_uart_bl_pdev_remove() can remove the serdev */
>    375		platform_set_drvdata(pdev, serdev);
>    376		return 0;
>    377	
>    378	err_remove_serdev:
>    379		serdev_device_remove(serdev);
>    380		return ret;
>    381	}
>    382	
> 
> --
> 0-DAY CI Kernel Test Service
> https://github.com/intel/lkp-tests/wiki

Because of the missing "2/3" in the subject line it likely has applied
it as first patch. I assume that was by mistake, given you also resent
the same patch again with the correct subject line.

Anyway, this report should be meaningless.

Thanks
- Markus Probst


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