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

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

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