[PATCH v5 1/3] serdev: handle devices without an ACPI or device tree node
From: ChunAn Wu
Date: Sat Oct 24 2026 - 08:07:38 EST
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@xxxxxxxxxxxxx>
---
MAINTAINERS | 1 +
.../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/serdev.h | 12 +++-
6 files changed, 86 insertions(+), 12 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@xxxxxxxxxxxxxxx
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..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/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