platform: chrome: Add cros-usbpd-notify driver

ChromiumOS uses ACPI device with HID "GOOG0003" for power delivery
related events. The existing cros-usbpd-charger driver relies on these
events without ever actually receiving them on ACPI platforms. This is
because in the ChromeOS kernel trees, the GOOG0003 device is owned by an
ACPI driver that offers firmware updates to USB-C chargers.

Introduce a new platform driver under cros-ec, the ChromeOS embedded
controller, that handles these PD events and dispatches them
appropriately over a notifier chain to all drivers that use them.

On platforms that don't have the ACPI device defined, the driver gets
instantiated for ECs which support the EC_FEATURE_USB_PD feature bit,
and the notification events will get delivered using the MKBP event
handling mechanism.

Co-Developed-by: Prashant Malani <[e-mail]>
Reviewed-by: Gwendal Grignou <[e-mail]>
Reviewed-by: Benson Leung <[e-mail]>
Signed-off-by: Jon Flatley <[e-mail]>
Signed-off-by: Prashant Malani <[e-mail]>
Acked-By: Enric Balletbo i Serra <[e-mail]>
Signed-off-by: Benson Leung <[e-mail]>

drivers/platform/chrome/Kconfig

···
 	  To compile this driver as a module, choose M here: the
 	  module will be called cros_usbpd_logger.
 
+config CROS_USBPD_NOTIFY
+	tristate "ChromeOS Type-C power delivery event notifier"
+	depends on MFD_CROS_EC_DEV
+	default MFD_CROS_EC_DEV
+	help
+	  If you say Y here, you get support for Type-C PD event notifications
+	  from the ChromeOS EC. On ACPI platorms this driver will bind to the
+	  GOOG0003 ACPI device, and on platforms which don't have this device it
+	  will get initialized on ECs which support the feature
+	  EC_FEATURE_USB_PD.
+
+	  To compile this driver as a module, choose M here: the
+	  module will be called cros_usbpd_notify.
+
 source "drivers/platform/chrome/wilco_ec/Kconfig"
 
 endif # CHROMEOS_PLATFORMS

drivers/platform/chrome/Makefile

···
 obj-$(CONFIG_CROS_EC_SENSORHUB)		+= cros_ec_sensorhub.o
 obj-$(CONFIG_CROS_EC_SYSFS)		+= cros_ec_sysfs.o
 obj-$(CONFIG_CROS_USBPD_LOGGER)		+= cros_usbpd_logger.o
+obj-$(CONFIG_CROS_USBPD_NOTIFY)		+= cros_usbpd_notify.o
 
 obj-$(CONFIG_WILCO_EC)			+= wilco_ec/

drivers/platform/chrome/cros_usbpd_notify.c

···
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright 2020 Google LLC
+ *
+ * This driver serves as the receiver of cros_ec PD host events.
+ */
+
+#include <linux/acpi.h>
+#include <linux/module.h>
+#include <linux/platform_data/cros_ec_proto.h>
+#include <linux/platform_data/cros_usbpd_notify.h>
+#include <linux/platform_device.h>
+
+#define DRV_NAME "cros-usbpd-notify"
+#define ACPI_DRV_NAME "GOOG0003"
+
+static BLOCKING_NOTIFIER_HEAD(cros_usbpd_notifier_list);
+
+/**
+ * cros_usbpd_register_notify - Register a notifier callback for PD events.
+ * @nb: Notifier block pointer to register
+ *
+ * On ACPI platforms this corresponds to host events on the ECPD
+ * "GOOG0003" ACPI device. On non-ACPI platforms this will filter mkbp events
+ * for USB PD events.
+ *
+ * Return: 0 on success or negative error code.
+ */
+int cros_usbpd_register_notify(struct notifier_block *nb)
+{
+	return blocking_notifier_chain_register(&cros_usbpd_notifier_list,
+						nb);
+}
+EXPORT_SYMBOL_GPL(cros_usbpd_register_notify);
+
+/**
+ * cros_usbpd_unregister_notify - Unregister notifier callback for PD events.
+ * @nb: Notifier block pointer to unregister
+ *
+ * Unregister a notifier callback that was previously registered with
+ * cros_usbpd_register_notify().
+ */
+void cros_usbpd_unregister_notify(struct notifier_block *nb)
+{
+	blocking_notifier_chain_unregister(&cros_usbpd_notifier_list, nb);
+}
+EXPORT_SYMBOL_GPL(cros_usbpd_unregister_notify);
+
+#ifdef CONFIG_ACPI
+
+static int cros_usbpd_notify_add_acpi(struct acpi_device *adev)
+{
+	return 0;
+}
+
+static void cros_usbpd_notify_acpi(struct acpi_device *adev, u32 event)
+{
+	blocking_notifier_call_chain(&cros_usbpd_notifier_list, event, NULL);
+}
+
+static const struct acpi_device_id cros_usbpd_notify_acpi_device_ids[] = {
+	{ ACPI_DRV_NAME, 0 },
+	{ }
+};
+MODULE_DEVICE_TABLE(acpi, cros_usbpd_notify_acpi_device_ids);
+
+static struct acpi_driver cros_usbpd_notify_acpi_driver = {
+	.name = DRV_NAME,
+	.class = DRV_NAME,
+	.ids = cros_usbpd_notify_acpi_device_ids,
+	.ops = {
+		.add = cros_usbpd_notify_add_acpi,
+		.notify = cros_usbpd_notify_acpi,
+	},
+};
+
+#endif /* CONFIG_ACPI */
+
+static int cros_usbpd_notify_plat(struct notifier_block *nb,
+				  unsigned long queued_during_suspend,
+				  void *data)
+{
+	struct cros_ec_device *ec_dev = (struct cros_ec_device *)data;
+	u32 host_event = cros_ec_get_host_event(ec_dev);
+
+	if (!host_event)
+		return NOTIFY_BAD;
+
+	if (host_event & EC_HOST_EVENT_MASK(EC_HOST_EVENT_PD_MCU)) {
+		blocking_notifier_call_chain(&cros_usbpd_notifier_list,
+					     host_event, NULL);
+		return NOTIFY_OK;
+	}
+	return NOTIFY_DONE;
+}
+
+static int cros_usbpd_notify_probe_plat(struct platform_device *pdev)
+{
+	struct device *dev = &pdev->dev;
+	struct cros_ec_dev *ecdev = dev_get_drvdata(dev->parent);
+	struct notifier_block *nb;
+	int ret;
+
+	nb = devm_kzalloc(dev, sizeof(*nb), GFP_KERNEL);
+	if (!nb)
+		return -ENOMEM;
+
+	nb->notifier_call = cros_usbpd_notify_plat;
+	dev_set_drvdata(dev, nb);
+
+	ret = blocking_notifier_chain_register(&ecdev->ec_dev->event_notifier,
+					       nb);
+	if (ret < 0) {
+		dev_err(dev, "Failed to register notifier\n");
+		return ret;
+	}
+
+	return 0;
+}
+
+static int cros_usbpd_notify_remove_plat(struct platform_device *pdev)
+{
+	struct device *dev = &pdev->dev;
+	struct cros_ec_dev *ecdev = dev_get_drvdata(dev->parent);
+	struct notifier_block *nb =
+		(struct notifier_block *)dev_get_drvdata(dev);
+
+	blocking_notifier_chain_unregister(&ecdev->ec_dev->event_notifier, nb);
+
+	return 0;
+}
+
+static struct platform_driver cros_usbpd_notify_plat_driver = {
+	.driver = {
+		.name = DRV_NAME,
+	},
+	.probe = cros_usbpd_notify_probe_plat,
+	.remove = cros_usbpd_notify_remove_plat,
+};
+
+static int __init cros_usbpd_notify_init(void)
+{
+	int ret;
+
+	ret = platform_driver_register(&cros_usbpd_notify_plat_driver);
+	if (ret < 0)
+		return ret;
+
+#ifdef CONFIG_ACPI
+	acpi_bus_register_driver(&cros_usbpd_notify_acpi_driver);
+#endif
+	return 0;
+}
+
+static void __exit cros_usbpd_notify_exit(void)
+{
+#ifdef CONFIG_ACPI
+	acpi_bus_unregister_driver(&cros_usbpd_notify_acpi_driver);
+#endif
+	platform_driver_unregister(&cros_usbpd_notify_plat_driver);
+}
+
+module_init(cros_usbpd_notify_init);
+module_exit(cros_usbpd_notify_exit);
+
+MODULE_LICENSE("GPL");
+MODULE_DESCRIPTION("ChromeOS power delivery notifier device");
+MODULE_AUTHOR("Jon Flatley <[e-mail]>");
+MODULE_ALIAS("platform:" DRV_NAME);

include/linux/platform_data/cros_usbpd_notify.h

···
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * ChromeOS EC Power Delivery Notifier Driver
+ *
+ * Copyright 2020 Google LLC
+ */
+
+#ifndef __LINUX_PLATFORM_DATA_CROS_USBPD_NOTIFY_H
+#define __LINUX_PLATFORM_DATA_CROS_USBPD_NOTIFY_H
+
+#include <linux/notifier.h>
+
+int cros_usbpd_register_notify(struct notifier_block *nb);
+
+void cros_usbpd_unregister_notify(struct notifier_block *nb);
+
+#endif  /* __LINUX_PLATFORM_DATA_CROS_USBPD_NOTIFY_H */