usb: typec: Add support for retimers

Introduce a retimer device class and associated functions that register
and use retimer "switch" devices. These operate in a manner similar to
the "mode-switch" and help configure retimers that exist between the
Type-C connector and host controller(s).

Type C ports can be linked to retimers using firmware node device
references (again, in a manner similar to "mode-switch").

There are no new sysfs files being created; there is the new retimer
class directory, but there are no class-specific files being created
there.

Signed-off-by: Prashant Malani <[e-mail]>
Acked-by: Heikki Krogerus <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/usb/typec/Makefile

···
 # SPDX-License-Identifier: GPL-2.0
 obj-$(CONFIG_TYPEC)		+= typec.o
-typec-y				:= class.o mux.o bus.o pd.o
+typec-y				:= class.o mux.o bus.o pd.o retimer.o
 typec-$(CONFIG_ACPI)		+= port-mapper.o
 obj-$(CONFIG_TYPEC)		+= altmodes/
 obj-$(CONFIG_TYPEC_TCPM)	+= tcpm/

drivers/usb/typec/class.c

···
 	if (ret)
 		goto err_unregister_bus;
 
-	ret = class_register(&typec_class);
+	ret = class_register(&retimer_class);
 	if (ret)
 		goto err_unregister_mux_class;
+
+	ret = class_register(&typec_class);
+	if (ret)
+		goto err_unregister_retimer_class;
 
 	ret = usb_power_delivery_init();
 	if (ret)
···
 
 err_unregister_class:
 	class_unregister(&typec_class);
+
+err_unregister_retimer_class:
+	class_unregister(&retimer_class);
 
 err_unregister_mux_class:
 	class_unregister(&typec_mux_class);

drivers/usb/typec/class.h

···
 #define is_typec_port(dev) ((dev)->type == &typec_port_dev_type)
 
 extern struct class typec_mux_class;
+extern struct class retimer_class;
 extern struct class typec_class;
 
 #if defined(CONFIG_ACPI)

drivers/usb/typec/retimer.c

···
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright 2022 Google LLC
+ *
+ * USB Type-C Retimer support.
+ * Author: Prashant Malani <[e-mail]>
+ *
+ */
+
+#include <linux/device.h>
+#include <linux/list.h>
+#include <linux/module.h>
+#include <linux/mutex.h>
+#include <linux/property.h>
+#include <linux/slab.h>
+
+#include "class.h"
+#include "retimer.h"
+
+static bool dev_name_ends_with(struct device *dev, const char *suffix)
+{
+	const char *name = dev_name(dev);
+	const int name_len = strlen(name);
+	const int suffix_len = strlen(suffix);
+
+	if (suffix_len > name_len)
+		return false;
+
+	return strcmp(name + (name_len - suffix_len), suffix) == 0;
+}
+
+static int retimer_fwnode_match(struct device *dev, const void *fwnode)
+{
+	return dev_fwnode(dev) == fwnode && dev_name_ends_with(dev, "-retimer");
+}
+
+static void *typec_retimer_match(struct fwnode_handle *fwnode, const char *id, void *data)
+{
+	struct device *dev  = class_find_device(&retimer_class, NULL, fwnode,
+						retimer_fwnode_match);
+
+	return dev ? to_typec_retimer(dev) : ERR_PTR(-EPROBE_DEFER);
+}
+
+/**
+ * fwnode_typec_retimer_get - Find USB Type-C retimer.
+ * @fwnode: The caller device node.
+ *
+ * Finds a retimer linked to the caller. This function is primarily meant for the
+ * Type-C drivers. Returns a reference to the retimer on success, NULL if no
+ * matching connection was found, or ERR_PTR(-EPROBE_DEFER) when a connection
+ * was found but the retimer has not been enumerated yet.
+ */
+struct typec_retimer *fwnode_typec_retimer_get(struct fwnode_handle *fwnode)
+{
+	struct typec_retimer *retimer;
+
+	retimer = fwnode_connection_find_match(fwnode, "retimer-switch", NULL, typec_retimer_match);
+	if (!IS_ERR_OR_NULL(retimer))
+		WARN_ON(!try_module_get(retimer->dev.parent->driver->owner));
+
+	return retimer;
+}
+EXPORT_SYMBOL_GPL(fwnode_typec_retimer_get);
+
+/**
+ * typec_retimer_put - Release handle to a retimer.
+ * @retimer: USB Type-C Connector Retimer.
+ *
+ * Decrements reference count for @retimer.
+ */
+void typec_retimer_put(struct typec_retimer *retimer)
+{
+	if (!IS_ERR_OR_NULL(retimer)) {
+		module_put(retimer->dev.parent->driver->owner);
+		put_device(&retimer->dev);
+	}
+}
+EXPORT_SYMBOL_GPL(typec_retimer_put);
+
+int typec_retimer_set(struct typec_retimer *retimer, struct typec_retimer_state *state)
+{
+	if (IS_ERR_OR_NULL(retimer))
+		return 0;
+
+	return retimer->set(retimer, state);
+}
+EXPORT_SYMBOL_GPL(typec_retimer_set);
+
+static void typec_retimer_release(struct device *dev)
+{
+	kfree(to_typec_retimer(dev));
+}
+
+static const struct device_type typec_retimer_dev_type = {
+	.name = "typec_retimer",
+	.release = typec_retimer_release,
+};
+
+/**
+ * typec_retimer_register - Register a retimer device.
+ * @parent: Parent device.
+ * @desc: Retimer description.
+ *
+ * Some USB Type-C connectors have their physical lines routed through retimers before they
+ * reach muxes or host controllers. In some cases (for example: using alternate modes)
+ * these retimers need to be reconfigured appropriately. This function registers retimer
+ * switches which route and potentially modify the signals on the Type C physical lines
+ * enroute to the host controllers.
+ */
+struct typec_retimer *
+typec_retimer_register(struct device *parent, const struct typec_retimer_desc *desc)
+{
+	struct typec_retimer *retimer;
+	int ret;
+
+	if (!desc || !desc->set)
+		return ERR_PTR(-EINVAL);
+
+	retimer = kzalloc(sizeof(*retimer), GFP_KERNEL);
+	if (!retimer)
+		return ERR_PTR(-ENOMEM);
+
+	retimer->set = desc->set;
+
+	device_initialize(&retimer->dev);
+	retimer->dev.parent = parent;
+	retimer->dev.fwnode = desc->fwnode;
+	retimer->dev.class = &retimer_class;
+	retimer->dev.type = &typec_retimer_dev_type;
+	retimer->dev.driver_data = desc->drvdata;
+	dev_set_name(&retimer->dev, "%s-retimer",
+		     desc->name ? desc->name : dev_name(parent));
+
+	ret = device_add(&retimer->dev);
+	if (ret) {
+		dev_err(parent, "failed to register retimer (%d)\n", ret);
+		put_device(&retimer->dev);
+		return ERR_PTR(ret);
+	}
+
+	return retimer;
+}
+EXPORT_SYMBOL_GPL(typec_retimer_register);
+
+/**
+ * typec_retimer_unregister - Unregister retimer device.
+ * @retimer: USB Type-C Connector retimer.
+ *
+ * Unregister retimer that was registered with typec_retimer_register().
+ */
+void typec_retimer_unregister(struct typec_retimer *retimer)
+{
+	if (!IS_ERR_OR_NULL(retimer))
+		device_unregister(&retimer->dev);
+}
+EXPORT_SYMBOL_GPL(typec_retimer_unregister);
+
+void *typec_retimer_get_drvdata(struct typec_retimer *retimer)
+{
+	return dev_get_drvdata(&retimer->dev);
+}
+EXPORT_SYMBOL_GPL(typec_retimer_get_drvdata);
+
+struct class retimer_class = {
+	.name = "retimer",
+	.owner = THIS_MODULE,
+};

drivers/usb/typec/retimer.h

···
+/* SPDX-License-Identifier: GPL-2.0 */
+
+#ifndef __USB_TYPEC_RETIMER__
+#define __USB_TYPEC_RETIMER__
+
+#include <linux/usb/typec_retimer.h>
+
+struct typec_retimer {
+	struct device dev;
+	typec_retimer_set_fn_t set;
+};
+
+#define to_typec_retimer(_dev_) container_of(_dev_, struct typec_retimer, dev)
+
+#endif /* __USB_TYPEC_RETIMER__ */

include/linux/usb/typec_retimer.h

···
+/* SPDX-License-Identifier: GPL-2.0 */
+
+#ifndef __USB_TYPEC_RETIMER
+#define __USB_TYPEC_RETIMER
+
+#include <linux/property.h>
+#include <linux/usb/typec.h>
+
+struct device;
+struct typec_retimer;
+struct typec_altmode;
+struct fwnode_handle;
+
+struct typec_retimer_state {
+	struct typec_altmode *alt;
+	unsigned long mode;
+	void *data;
+};
+
+typedef int (*typec_retimer_set_fn_t)(struct typec_retimer *retimer,
+				      struct typec_retimer_state *state);
+
+struct typec_retimer_desc {
+	struct fwnode_handle *fwnode;
+	typec_retimer_set_fn_t set;
+	const char *name;
+	void *drvdata;
+};
+
+struct typec_retimer *fwnode_typec_retimer_get(struct fwnode_handle *fwnode);
+void typec_retimer_put(struct typec_retimer *retimer);
+int typec_retimer_set(struct typec_retimer *retimer, struct typec_retimer_state *state);
+
+static inline struct typec_retimer *typec_retimer_get(struct device *dev)
+{
+	return fwnode_typec_retimer_get(dev_fwnode(dev));
+}
+
+struct typec_retimer *
+typec_retimer_register(struct device *parent, const struct typec_retimer_desc *desc);
+void typec_retimer_unregister(struct typec_retimer *retimer);
+
+void *typec_retimer_get_drvdata(struct typec_retimer *retimer);
+
+#endif /* __USB_TYPEC_RETIMER */