[PATCH v6 0/3] serdev: handle devices without an ACPI or device tree node

[PATCH v6 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 v6:
- Patch 1: switch dell-uart-backlight and yoga-tab2-pro-1380
  fastcharger over to the new serdev_device_add() signature with
  modalias=NULL so the tree keeps building through patch 1; patches
  2/3 then switch them to a real modalias. Fixes the bisect break
  that sashiko-bot flagged (true positive, Markus Probst confirmed).
- Patch 1: wire up struct serdev_device_id in modpost, modelled on
  the SPI bus: new DEVID() + DEVID_FIELD() entries in
  scripts/mod/devicetable-offsets.c, do_serdev_entry() and devtable[]
  entry in scripts/mod/file2alias.c, and the device-id/serdev.h
  include in include/linux/mod_devicetable.h. Also add
  serdev_device_id to scripts/coccinelle/misc/of_table.cocci.
  Reported by sashiko-bot; the two in-tree firmware-less clients do
  not need MODULE_DEVICE_TABLE(serdev, ...) because the same module
  creates and drives their serdev child, but the plumbing matches
  the other buses in case out-of-tree users want it. Markus Probst
  confirmed as true positive.
- Patch 1: drop the unused `#include <linux/string.h>` from
  include/linux/serdev.h. strscpy() is used only in core.c, which
  already pulls string.h transitively. Reported by Markus Probst.
- Patch 1: drop Markus's v5 Reviewed-by. The modpost wiring and the
  dell/yoga NULL-stub bisect fix are new code he has not seen; the
  tag belongs on code that was actually reviewed.
- Patch 3: drop the "serdev driver MUST be registered first" comment
  in yt2_1380_fc_module_init(). With id_table matching the order of
  driver_register vs device_add no longer matters. Reported by
  Markus Probst.

Changes in v5:
- Patch 1: restore is_serdev_device() guard at the top of
  serdev_device_match(). Dropping it was correct when match only
  called acpi/of helpers, but Patch 1 also adds
  serdev_match_id(sdrv->id_table, serdev->modalias), which
  dereferences serdev_device-only memory. Since serdev_controller
  shares serdev_bus_type, the driver core calls .match on controllers
  too; without the guard, serdev->modalias on a controller reads bytes
  from inside host/nr/serdev/ops, and strcmp() can walk past the end of
  the controller struct. Reported by sashiko-bot on 2/3 and 3/3.

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

v5: https://lore.kernel.org/lkml/cover.1792831564.git.an.wu@canonical.com/
v4: https://lore.kernel.org/lkml/20261024022930.2704030-1-an.wu@canonical.com/
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   | 18 +++---
 .../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                     | 62 ++++++++++++++++---
 include/linux/device-id/serdev.h              | 19 ++++++
 include/linux/mod_devicetable.h               |  1 +
 include/linux/serdev.h                        | 11 +++-
 scripts/coccinelle/misc/of_table.cocci        | 16 ++---
 scripts/mod/devicetable-offsets.c             |  3 +
 scripts/mod/file2alias.c                      |  9 +++
 12 files changed, 120 insertions(+), 49 deletions(-)
 create mode 100644 include/linux/device-id/serdev.h


base-commit: 9e947d96915af63e28896caae85a81b74855621b
-- 
2.34.1

[PATCH v6 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, and wire the new ID struct up in file2alias and
the of_table coccinelle check.

Update the existing serdev_device_add() callers to pass NULL. The two
in-tree firmware-less clients (dell-uart-backlight, yoga-tab2-pro-1380
fastcharger) also pass NULL here so the tree keeps building across the
series; the two following patches switch them to a real modalias and
drop their force_attach workarounds.

Signed-off-by: ChunAn Wu <an.wu@canonical.com>
---
 MAINTAINERS                                   |  1 +
 .../platform/x86/dell/dell-uart-backlight.c   |  2 +-
 .../lenovo/yoga-tab2-pro-1380-fastcharger.c   |  2 +-
 .../platform/x86/x86-android-tablets/core.c   |  2 +-
 drivers/power/sequencing/pwrseq-pcie-m2.c     |  2 +-
 drivers/tty/serdev/core.c                     | 62 ++++++++++++++++---
 include/linux/device-id/serdev.h              | 19 ++++++
 include/linux/mod_devicetable.h               |  1 +
 include/linux/serdev.h                        | 11 +++-
 scripts/coccinelle/misc/of_table.cocci        | 16 ++---
 scripts/mod/devicetable-offsets.c             |  3 +
 scripts/mod/file2alias.c                      |  9 +++
 12 files changed, 108 insertions(+), 22 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/dell/dell-uart-backlight.c b/drivers/platform/x86/dell/dell-uart-backlight.c
index f323a667dc2d..f076cfac2bc5 100644
--- a/drivers/platform/x86/dell/dell-uart-backlight.c
+++ b/drivers/platform/x86/dell/dell-uart-backlight.c
@@ -354,7 +354,7 @@ 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, NULL);
 	if (ret) {
 		dev_err(&pdev->dev, "error %d adding serdev\n", ret);
 		serdev_device_put(serdev);
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..5e568fe1162d 100644
--- a/drivers/platform/x86/lenovo/yoga-tab2-pro-1380-fastcharger.c
+++ b/drivers/platform/x86/lenovo/yoga-tab2-pro-1380-fastcharger.c
@@ -260,7 +260,7 @@ 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, NULL);
 	if (ret) {
 		serdev_device_put(serdev);
 		return dev_err_probe(&pdev->dev, ret, "adding serdev\n");
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..e0517d5a48da 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)
@@ -86,28 +101,57 @@ 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)
 {
+	const struct serdev_device *serdev;
+	const struct serdev_device_driver *sdrv;
+
 	if (!is_serdev_device(dev))
 		return 0;
 
-	/* TODO: platform matching */
+	serdev = to_serdev_device(dev);
+	sdrv = to_serdev_device_driver(drv);
+
 	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 +597,7 @@ 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 +751,7 @@ 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/mod_devicetable.h b/include/linux/mod_devicetable.h
index 318c4b5c3451..4cb18c41254a 100644
--- a/include/linux/mod_devicetable.h
+++ b/include/linux/mod_devicetable.h
@@ -52,6 +52,7 @@
 #include "device-id/rpmsg.h"
 #include "device-id/sdio.h"
 #include "device-id/sdw.h"
+#include "device-id/serdev.h"
 #include "device-id/serio.h"
 #include "device-id/slim.h"
 #include "device-id/spi.h"
diff --git a/include/linux/serdev.h b/include/linux/serdev.h
index b6c3d957ec15..81528c69456a 100644
--- a/include/linux/serdev.h
+++ b/include/linux/serdev.h
@@ -7,6 +7,7 @@
 
 #include <linux/types.h>
 #include <linux/device.h>
+#include <linux/device-id/serdev.h>
 #include <linux/iopoll.h>
 #include <linux/uaccess.h>
 #include <linux/termios.h>
@@ -35,6 +36,10 @@ 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 +48,7 @@ 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 +61,15 @@ 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 +167,7 @@ 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,
diff --git a/scripts/coccinelle/misc/of_table.cocci b/scripts/coccinelle/misc/of_table.cocci
index 17881cb0884b..3b6dc2c13703 100644
--- a/scripts/coccinelle/misc/of_table.cocci
+++ b/scripts/coccinelle/misc/of_table.cocci
@@ -1,7 +1,7 @@
 // SPDX-License-Identifier: GPL-2.0
-/// Make sure (of/i2c/platform/spi)_device_id tables are NULL terminated
+/// Make sure (of/i2c/platform/serdev/spi)_device_id tables are NULL terminated
 //
-// Keywords: of_table i2c_table platform_table
+// Keywords: of_table i2c_table platform_table serdev_table
 // Confidence: Medium
 // Options: --include-headers
 
@@ -15,14 +15,14 @@ identifier var, arr;
 expression E;
 @@
 (
-struct \(of_device_id \| i2c_device_id \| platform_device_id \| spi_device_id\) arr[] = {
+struct \(of_device_id \| i2c_device_id \| platform_device_id \| serdev_device_id \| spi_device_id\) arr[] = {
 	...,
 	{
 	.var = E,
 *	}
 };
 |
-struct \(of_device_id \| i2c_device_id \| platform_device_id \| spi_device_id\) arr[] = {
+struct \(of_device_id \| i2c_device_id \| platform_device_id \| serdev_device_id \| spi_device_id\) arr[] = {
 	...,
 *	{ ..., E, ... },
 };
@@ -33,7 +33,7 @@ identifier var, arr;
 expression E;
 @@
 (
-struct \(of_device_id \| i2c_device_id \| platform_device_id \| spi_device_id\) arr[] = {
+struct \(of_device_id \| i2c_device_id \| platform_device_id \| serdev_device_id \| spi_device_id\) arr[] = {
 	...,
 	{
 	.var = E,
@@ -42,7 +42,7 @@ struct \(of_device_id \| i2c_device_id \| platform_device_id \| spi_device_id\)
 +	{ }
 };
 |
-struct \(of_device_id \| i2c_device_id \| platform_device_id \| spi_device_id\) arr[] = {
+struct \(of_device_id \| i2c_device_id \| platform_device_id \| serdev_device_id \| spi_device_id\) arr[] = {
 	...,
 	{ ..., E, ... },
 +	{ },
@@ -55,7 +55,7 @@ identifier var, arr;
 expression E;
 @@
 (
-struct \(of_device_id \| i2c_device_id \| platform_device_id \| spi_device_id\) arr[] = {
+struct \(of_device_id \| i2c_device_id \| platform_device_id \| serdev_device_id \| spi_device_id\) arr[] = {
 	...,
 	{
 	.var = E,
@@ -63,7 +63,7 @@ struct \(of_device_id \| i2c_device_id \| platform_device_id \| spi_device_id\)
 	@p1
 };
 |
-struct \(of_device_id \| i2c_device_id \| platform_device_id \| spi_device_id\) arr[] = {
+struct \(of_device_id \| i2c_device_id \| platform_device_id \| serdev_device_id \| spi_device_id\) arr[] = {
 	...,
 	{ ..., E, ... }
 	@p1
diff --git a/scripts/mod/devicetable-offsets.c b/scripts/mod/devicetable-offsets.c
index 1492e9fdc7cb..522bea285c7a 100644
--- a/scripts/mod/devicetable-offsets.c
+++ b/scripts/mod/devicetable-offsets.c
@@ -158,6 +158,9 @@ int main(void)
 	DEVID_FIELD(slim_device_id, manf_id);
 	DEVID_FIELD(slim_device_id, prod_code);
 
+	DEVID(serdev_device_id);
+	DEVID_FIELD(serdev_device_id, name);
+
 	DEVID(spi_device_id);
 	DEVID_FIELD(spi_device_id, name);
 
diff --git a/scripts/mod/file2alias.c b/scripts/mod/file2alias.c
index 980d7da456bb..552847deab94 100644
--- a/scripts/mod/file2alias.c
+++ b/scripts/mod/file2alias.c
@@ -886,6 +886,14 @@ static void do_slim_entry(struct module *mod, void *symval)
 	module_alias_printf(mod, false, "slim:%x:%x:*", manf_id, prod_code);
 }
 
+/* Looks like: serial:S */
+static void do_serdev_entry(struct module *mod, void *symval)
+{
+	DEF_FIELD_ADDR(symval, serdev_device_id, name);
+
+	module_alias_printf(mod, false, SERDEV_MODULE_PREFIX "%s", *name);
+}
+
 /* Looks like: spi:S */
 static void do_spi_entry(struct module *mod, void *symval)
 {
@@ -1500,6 +1508,7 @@ static const struct devtable devtable[] = {
 	{"rpmsg", SIZE_rpmsg_device_id, do_rpmsg_entry},
 	{"i2c", SIZE_i2c_device_id, do_i2c_entry},
 	{"i3c", SIZE_i3c_device_id, do_i3c_entry},
+	{"serdev", SIZE_serdev_device_id, do_serdev_entry},
 	{"slim", SIZE_slim_device_id, do_slim_entry},
 	{"spi", SIZE_spi_device_id, do_spi_entry},
 	{"dmi", SIZE_dmi_system_id, do_dmi_entry},
-- 
2.34.1

[PATCH v6 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>
Reviewed-by: Markus Probst <markus.probst@posteo.de>
---
 .../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 f076cfac2bc5..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, NULL);
+	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 v6 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>
Reviewed-by: Markus Probst <markus.probst@posteo.de>
---
 .../lenovo/yoga-tab2-pro-1380-fastcharger.c   | 25 ++++++-------------
 1 file changed, 7 insertions(+), 18 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 5e568fe1162d..ecac3eb3f336 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, NULL);
+	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;
@@ -304,10 +297,6 @@ 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.
-	 */
 	ret = serdev_device_driver_register(&yt2_1380_fc_serdev_driver);
 	if (ret)
 		return ret;
-- 
2.34.1