[PATCH v3 1/1] platform/chrome: add a driver for HPS

[Sami Kyöstilä]

This patch introduces a driver for the ChromeOS screen privacy
sensor (aka. HPS). The driver supports a sensor connected to the I2C bus
and identified as "GOOG0020" in the ACPI tables.

When loaded, the driver exports the sensor to userspace through a
character device. This device only supports power management, i.e.,
communication with the sensor must be done through regular I2C
transmissions from userspace.

Power management is implemented by enabling the respective power GPIO
while at least one userspace process holds an open fd on the character
device. By default, the device is powered down if there are no active
clients.

Note that the driver makes no effort to preserve the state of the sensor
between power down and power up events. Userspace is responsible for
reinitializing any needed state once power has been restored.

The device firmware, I2C protocol and other documentation is available
at https://chromium.googlesource.com/chromiumos/platform/hps-firmware.

Signed-off-by: Sami Kyöstilä <skyostil@xxxxxxxxxxxx>
---

Changes in v3:
- Moved from drivers/misc to drivers/platform/chrome.

Changes in v2:
- Removed custom ioctl interface.
- Reworked to use miscdev.

 MAINTAINERS                            |   6 +
 drivers/platform/chrome/Kconfig        |  10 ++
 drivers/platform/chrome/Makefile       |   1 +
 drivers/platform/chrome/cros_hps_i2c.c | 184 +++++++++++++++++++++++++
 4 files changed, 201 insertions(+)
 create mode 100644 drivers/platform/chrome/cros_hps_i2c.c

diff --git a/MAINTAINERS b/MAINTAINERS
index 69a2935daf6c..94a8c178598e 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -8800,6 +8800,12 @@ S:	Maintained
 W:	http://artax.karlin.mff.cuni.cz/~mikulas/vyplody/hpfs/index-e.cgi
 F:	fs/hpfs/
 
+HPS (ChromeOS screen privacy sensor) DRIVER
+M:	Sami Kyöstilä <skyostil@xxxxxxxxxxxx>
+R:	Evan Benn <evanbenn@xxxxxxxxxxxx>
+S:	Maintained
+F:	drivers/platform/chrome/cros_hps_i2c.c
+
 HSI SUBSYSTEM
 M:	Sebastian Reichel <sre@xxxxxxxxxx>
 S:	Maintained
diff --git a/drivers/platform/chrome/Kconfig b/drivers/platform/chrome/Kconfig
index ccc23d8686e8..a20da7b638df 100644
--- a/drivers/platform/chrome/Kconfig
+++ b/drivers/platform/chrome/Kconfig
@@ -217,6 +217,16 @@ config CROS_EC_TYPEC
 	  To compile this driver as a module, choose M here: the module will be
 	  called cros_ec_typec.
 
+config CROS_HPS_I2C
+	tristate "ChromeOS HPS device"
+	depends on HID && I2C && PM
+	help
+	  Say Y here if you want to enable support for the ChromeOS
+	  screen privacy sensor (HPS), attached via I2C. The driver supports a
+	  sensor connected to the I2C bus and exposes it as a character device.
+	  To save power, the sensor is automatically powered down when no
+	  clients are accessing it.
+
 config CROS_USBPD_LOGGER
 	tristate "Logging driver for USB PD charger"
 	depends on CHARGER_CROS_USBPD
diff --git a/drivers/platform/chrome/Makefile b/drivers/platform/chrome/Makefile
index f901d2e43166..66bd745d5931 100644
--- a/drivers/platform/chrome/Makefile
+++ b/drivers/platform/chrome/Makefile
@@ -23,6 +23,7 @@ obj-$(CONFIG_CROS_EC_DEBUGFS)		+= cros_ec_debugfs.o
 cros-ec-sensorhub-objs			:= cros_ec_sensorhub.o cros_ec_sensorhub_ring.o cros_ec_trace.o
 obj-$(CONFIG_CROS_EC_SENSORHUB)		+= cros-ec-sensorhub.o
 obj-$(CONFIG_CROS_EC_SYSFS)		+= cros_ec_sysfs.o
+obj-$(CONFIG_CROS_HPS_I2C)		+= cros_hps_i2c.o
 obj-$(CONFIG_CROS_USBPD_LOGGER)		+= cros_usbpd_logger.o
 obj-$(CONFIG_CROS_USBPD_NOTIFY)		+= cros_usbpd_notify.o
 
diff --git a/drivers/platform/chrome/cros_hps_i2c.c b/drivers/platform/chrome/cros_hps_i2c.c
new file mode 100644
index 000000000000..9071c9324fa7
--- /dev/null
+++ b/drivers/platform/chrome/cros_hps_i2c.c
@@ -0,0 +1,184 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Driver for the ChromeOS screen privacy sensor (HPS), attached via I2C.
+ *
+ * The driver exposes HPS as a character device, although currently no read or
+ * write operations are supported. Instead, the driver only controls the power
+ * state of the sensor, keeping it on only while userspace holds an open file
+ * descriptor to the HPS device.
+ *
+ * Copyright 2022 Google LLC.
+ */
+
+#include <linux/acpi.h>
+#include <linux/fs.h>
+#include <linux/gpio/consumer.h>
+#include <linux/i2c.h>
+#include <linux/miscdevice.h>
+#include <linux/module.h>
+#include <linux/pm_runtime.h>
+
+#define HPS_ACPI_ID		"GOOG0020"
+
+struct hps_drvdata {
+	struct i2c_client *client;
+	struct miscdevice misc_device;
+	struct gpio_desc *enable_gpio;
+};
+
+static void hps_set_power(struct hps_drvdata *hps, bool state)
+{
+	if (!IS_ERR_OR_NULL(hps->enable_gpio))
+		gpiod_set_value_cansleep(hps->enable_gpio, state);
+}
+
+static void hps_unload(void *drv_data)
+{
+	struct hps_drvdata *hps = drv_data;
+
+	hps_set_power(hps, true);
+}
+
+static int hps_open(struct inode *inode, struct file *file)
+{
+	struct hps_drvdata *hps = container_of(file->private_data,
+					       struct hps_drvdata, misc_device);
+	struct device *dev = &hps->client->dev;
+	int ret;
+
+	ret = pm_runtime_get_sync(dev);
+	if (ret < 0)
+		goto pm_get_fail;
+	return 0;
+
+pm_get_fail:
+	pm_runtime_put(dev);
+	pm_runtime_disable(dev);
+	return ret;
+}
+
+static int hps_release(struct inode *inode, struct file *file)
+{
+	struct hps_drvdata *hps = container_of(file->private_data,
+					       struct hps_drvdata, misc_device);
+	struct device *dev = &hps->client->dev;
+	int ret;
+
+	ret = pm_runtime_put(dev);
+	if (ret < 0)
+		goto pm_put_fail;
+	return 0;
+
+pm_put_fail:
+	pm_runtime_disable(dev);
+	return ret;
+}
+
+const struct file_operations hps_fops = {
+	.owner = THIS_MODULE,
+	.open = hps_open,
+	.release = hps_release,
+};
+
+static int hps_i2c_probe(struct i2c_client *client)
+{
+	struct hps_drvdata *hps;
+	int ret = 0;
+
+	hps = devm_kzalloc(&client->dev, sizeof(*hps), GFP_KERNEL);
+	if (!hps)
+		return -ENOMEM;
+
+	memset(&hps->misc_device, 0, sizeof(hps->misc_device));
+	hps->misc_device.parent = &client->dev;
+	hps->misc_device.minor = MISC_DYNAMIC_MINOR;
+	hps->misc_device.name = "hps";
+	hps->misc_device.fops = &hps_fops;
+
+	i2c_set_clientdata(client, hps);
+	hps->client = client;
+	hps->enable_gpio = devm_gpiod_get(&client->dev, "enable", GPIOD_OUT_HIGH);
+	if (IS_ERR(hps->enable_gpio)) {
+		ret = PTR_ERR(hps->enable_gpio);
+		dev_err(&client->dev, "failed to get enable gpio: %d\n", ret);
+		return ret;
+	}
+
+	ret = devm_add_action(&client->dev, &hps_unload, hps);
+	if (ret) {
+		dev_err(&client->dev,
+			"failed to install unload action: %d\n", ret);
+		return ret;
+	}
+
+	ret = misc_register(&hps->misc_device);
+	if (ret) {
+		dev_err(&client->dev, "failed to initialize misc device: %d\n", ret);
+		return ret;
+	}
+
+	hps_set_power(hps, false);
+	pm_runtime_enable(&client->dev);
+	return ret;
+}
+
+static int hps_i2c_remove(struct i2c_client *client)
+{
+	struct hps_drvdata *hps = i2c_get_clientdata(client);
+
+	pm_runtime_disable(&client->dev);
+	misc_deregister(&hps->misc_device);
+	return 0;
+}
+
+static int hps_suspend(struct device *dev)
+{
+	struct i2c_client *client = to_i2c_client(dev);
+	struct hps_drvdata *hps = i2c_get_clientdata(client);
+
+	hps_set_power(hps, false);
+	return 0;
+}
+
+static int hps_resume(struct device *dev)
+{
+	struct i2c_client *client = to_i2c_client(dev);
+	struct hps_drvdata *hps = i2c_get_clientdata(client);
+
+	hps_set_power(hps, true);
+	return 0;
+}
+static UNIVERSAL_DEV_PM_OPS(hps_pm_ops, hps_suspend, hps_resume, NULL);
+
+static const struct i2c_device_id hps_i2c_id[] = {
+	{ "hps", 0 },
+	{ }
+};
+MODULE_DEVICE_TABLE(i2c, hps_i2c_id);
+
+#ifdef CONFIG_ACPI
+static const struct acpi_device_id hps_acpi_id[] = {
+	{ HPS_ACPI_ID, 0 },
+	{ }
+};
+MODULE_DEVICE_TABLE(acpi, hps_acpi_id);
+#endif /* CONFIG_ACPI */
+
+static struct i2c_driver hps_i2c_driver = {
+	.probe_new = hps_i2c_probe,
+	.remove = hps_i2c_remove,
+	.id_table = hps_i2c_id,
+	.driver = {
+		.name = "hps",
+		.pm = &hps_pm_ops,
+#ifdef CONFIG_ACPI
+		.acpi_match_table = ACPI_PTR(hps_acpi_id),
+#endif
+	},
+};
+module_i2c_driver(hps_i2c_driver);
+
+MODULE_ALIAS("acpi:" HPS_ACPI_ID);
+MODULE_AUTHOR("Sami Kyöstilä <skyostil@xxxxxxxxxxxx>");
+MODULE_DESCRIPTION("Driver for ChromeOS HPS");
+MODULE_LICENSE("GPL");
-- 
2.35.0.263.gb82422642f-goog