platform: chrome: Add Tablet Switch ACPI driver

Add a kernel driver for GOOG0006, an ACPI driver reporting an event when
the tablet switch status changes.

On an ACPI based convertible chromebook check evtest display tablet mode
switch changes:
Available devices:
..
/dev/input/event3:      Tablet Mode Switch
..
Testing ... (interrupt to exit)
Event: time 1484879712.604360, type 5 (EV_SW), code 1 (SW_TABLET_MODE),
value 1
Event: time 1484879712.604360, -------------- SYN_REPORT ------------
Event: time 1484879715.132228, type 5 (EV_SW), code 1 (SW_TABLET_MODE),
value 0
Event: time 1484879715.132228, -------------- SYN_REPORT ------------
...
Check state is updated at resume time when different from suspend time.

Signed-off-by: Gwendal Grignou <gwendal@chromium.org>
Signed-off-by: Benson Leung <bleung@chromium.org>

drivers/platform/chrome/Kconfig

@@ -38,6 +38,16 @@ config CHROMEOS_PSTORE
 	  If you have a supported Chromebook, choose Y or M here.
 	  The module will be called chromeos_pstore.
 
+config CHROMEOS_TBMC
+	tristate "ChromeOS Tablet Switch Controller"
+	depends on ACPI
+	help
+	  This option adds a driver for the tablet switch on
+	  select Chrome OS systems.
+
+	  To compile this driver as a module, choose M here: the
+	  module will be called chromeos_tbmc.
+
 config CROS_EC_CTL
         tristate
 

drivers/platform/chrome/Makefile

@@ -2,6 +2,7 @@
 
 obj-$(CONFIG_CHROMEOS_LAPTOP)		+= chromeos_laptop.o
 obj-$(CONFIG_CHROMEOS_PSTORE)		+= chromeos_pstore.o
+obj-$(CONFIG_CHROMEOS_TBMC)		+= chromeos_tbmc.o
 cros_ec_ctl-objs			:= cros_ec_sysfs.o cros_ec_lightbar.o \
 					   cros_ec_vbc.o cros_ec_debugfs.o
 obj-$(CONFIG_CROS_EC_CTL)		+= cros_ec_ctl.o

drivers/platform/chrome/chromeos_tbmc.c

@@ -0,0 +1,128 @@
+/*
+ * chromeos_tbmc - Driver to detect Tablet Mode for ChromeOS convertible.
+ *
+ * Copyright 2017 Google, Inc
+ *
+ * This software is licensed under the terms of the GNU General Public
+ * License version 2, as published by the Free Software Foundation, and
+ * may be copied, distributed, and modified under those terms.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * On Chromebook using ACPI, this device listens for notification
+ * from GOOG0006 and issue method TBMC to retrieve the status.
+ *
+ * GOOG0006 issues the notification when it receives EC_HOST_EVENT_MODE_CHANGE
+ * from the EC.
+ * Method TBMC reads EC_ACPI_MEM_DEVICE_ORIENTATION byte from the shared
+ * memory region.
+ */
+
+#include <linux/acpi.h>
+#include <linux/input.h>
+#include <linux/io.h>
+#include <linux/module.h>
+#include <linux/printk.h>
+
+#define DRV_NAME "chromeos_tbmc"
+#define ACPI_DRV_NAME "GOOG0006"
+
+static int chromeos_tbmc_query_switch(struct acpi_device *adev,
+				     struct input_dev *idev)
+{
+	unsigned long long state;
+	acpi_status status;
+
+	status = acpi_evaluate_integer(adev->handle, "TBMC", NULL, &state);
+	if (ACPI_FAILURE(status))
+		return -ENODEV;
+
+	/* input layer checks if event is redundant */
+	input_report_switch(idev, SW_TABLET_MODE, state);
+	input_sync(idev);
+
+	return 0;
+}
+
+static __maybe_unused int chromeos_tbmc_resume(struct device *dev)
+{
+	struct acpi_device *adev = to_acpi_device(dev);
+
+	return chromeos_tbmc_query_switch(adev, adev->driver_data);
+}
+
+static void chromeos_tbmc_notify(struct acpi_device *adev, u32 event)
+{
+	switch (event) {
+	case 0x80:
+		chromeos_tbmc_query_switch(adev, adev->driver_data);
+		break;
+	default:
+		dev_err(&adev->dev, "Unexpected event: 0x%08X\n", event);
+	}
+}
+
+static int chromeos_tbmc_open(struct input_dev *idev)
+{
+	struct acpi_device *adev = input_get_drvdata(idev);
+
+	return chromeos_tbmc_query_switch(adev, idev);
+}
+
+static int chromeos_tbmc_add(struct acpi_device *adev)
+{
+	struct input_dev *idev;
+	struct device *dev = &adev->dev;
+	int ret;
+
+	idev = devm_input_allocate_device(dev);
+	if (!idev)
+		return -ENOMEM;
+
+	idev->name = "Tablet Mode Switch";
+	idev->phys = acpi_device_hid(adev);
+
+	idev->id.bustype = BUS_HOST;
+	idev->id.version = 1;
+	idev->id.product = 0;
+	idev->open = chromeos_tbmc_open;
+
+	input_set_drvdata(idev, adev);
+	adev->driver_data = idev;
+
+	input_set_capability(idev, EV_SW, SW_TABLET_MODE);
+	ret = input_register_device(idev);
+	if (ret) {
+		dev_err(dev, "cannot register input device\n");
+		return ret;
+	}
+	return 0;
+}
+
+static const struct acpi_device_id chromeos_tbmc_acpi_device_ids[] = {
+	{ ACPI_DRV_NAME, 0 },
+	{ }
+};
+MODULE_DEVICE_TABLE(acpi, chromeos_tbmc_acpi_device_ids);
+
+static const SIMPLE_DEV_PM_OPS(chromeos_tbmc_pm_ops, NULL,
+		chromeos_tbmc_resume);
+
+static struct acpi_driver chromeos_tbmc_driver = {
+	.name = DRV_NAME,
+	.class = DRV_NAME,
+	.ids = chromeos_tbmc_acpi_device_ids,
+	.ops = {
+		.add = chromeos_tbmc_add,
+		.notify = chromeos_tbmc_notify,
+	},
+	.drv.pm = &chromeos_tbmc_pm_ops,
+};
+
+module_acpi_driver(chromeos_tbmc_driver);
+
+MODULE_LICENSE("GPL v2");
+MODULE_DESCRIPTION("ChromeOS ACPI tablet switch driver");