HID: i2c-hid: elan: Add support for Elan eKTH6915 i2c-hid touchscreens

Like many i2c-hid touchscreen controllers, the Elan eKTH6915 has a
reset GPIO hooked up to it. According to the datasheet, the way we're
supposed to turn the touchscreen on is:

1. Turn on the 3.3V supply.
2. Turn on the IO supply. It's OK if this is hardwired to the 3.3V
   supply, but if it's not then it must be turned on _after_ the 3.3V
   supply.
3. Wait >= 1 ms.
4. Deassert the reset GPIO (reset GPIO is active low, so there would
   be a leakage path if this was deasserted _before_ the IO supply).
5. Wait 300 ms.

Much of the above can be handled by the generic i2c-hid-of driver, but
the "reset" GPIO is not supported by that driver. Thus we'll do the
same as we did for Goodix and add a new tiny driver that uses the
i2c-hid core.

NOTE: support for this new touchscreen could theorically fit into the
Goodix driver. I've made it a separate driver because the Elan driver
supports _two_ regulators and it's unclear exactly how that would fit
in with commit 18eeef46 ("HID: i2c-hid: goodix: Tie the reset line
to true state of the regulator").
Signed-off-by: Douglas Anderson <dianders@chromium.org>
Reviewed-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>
Reviewed-by: Matthias Kaehlcke <mka@chromium.org>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>

drivers/hid/i2c-hid/Kconfig

@@ -32,6 +32,21 @@ config I2C_HID_OF
 	  will be called i2c-hid-of.  It will also build/depend on the
 	  module i2c-hid.
 
+config I2C_HID_OF_ELAN
+	tristate "Driver for Elan hid-i2c based devices on OF systems"
+	default n
+	depends on I2C && INPUT && OF
+	help
+	  Say Y here if you want support for Elan i2c devices that use
+	  the i2c-hid protocol on Open Firmware (Device Tree)-based
+	  systems.
+
+	  If unsure, say N.
+
+	  This support is also available as a module.  If so, the module
+	  will be called i2c-hid-of-elan.  It will also build/depend on
+	  the module i2c-hid.
+
 config I2C_HID_OF_GOODIX
 	tristate "Driver for Goodix hid-i2c based devices on OF systems"
 	default n

drivers/hid/i2c-hid/Makefile

@@ -10,4 +10,5 @@ i2c-hid-$(CONFIG_DMI)				+= i2c-hid-dmi-quirks.o
 
 obj-$(CONFIG_I2C_HID_ACPI)			+= i2c-hid-acpi.o
 obj-$(CONFIG_I2C_HID_OF)			+= i2c-hid-of.o
+obj-$(CONFIG_I2C_HID_OF_ELAN)			+= i2c-hid-of-elan.o
 obj-$(CONFIG_I2C_HID_OF_GOODIX)			+= i2c-hid-of-goodix.o

drivers/hid/i2c-hid/i2c-hid-of-elan.c

+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Driver for Elan touchscreens that use the i2c-hid protocol.
+ *
+ * Copyright 2020 Google LLC
+ */
+
+#include <linux/delay.h>
+#include <linux/device.h>
+#include <linux/gpio/consumer.h>
+#include <linux/i2c.h>
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/of.h>
+#include <linux/pm.h>
+#include <linux/regulator/consumer.h>
+
+#include "i2c-hid.h"
+
+struct elan_i2c_hid_chip_data {
+	unsigned int post_gpio_reset_delay_ms;
+	unsigned int post_power_delay_ms;
+	u16 hid_descriptor_address;
+};
+
+struct i2c_hid_of_elan {
+	struct i2chid_ops ops;
+
+	struct regulator *vcc33;
+	struct regulator *vccio;
+	struct gpio_desc *reset_gpio;
+	const struct elan_i2c_hid_chip_data *chip_data;
+};
+
+static int elan_i2c_hid_power_up(struct i2chid_ops *ops)
+{
+	struct i2c_hid_of_elan *ihid_elan =
+		container_of(ops, struct i2c_hid_of_elan, ops);
+	int ret;
+
+	ret = regulator_enable(ihid_elan->vcc33);
+	if (ret)
+		return ret;
+
+	ret = regulator_enable(ihid_elan->vccio);
+	if (ret) {
+		regulator_disable(ihid_elan->vcc33);
+		return ret;
+	}
+
+	if (ihid_elan->chip_data->post_power_delay_ms)
+		msleep(ihid_elan->chip_data->post_power_delay_ms);
+
+	gpiod_set_value_cansleep(ihid_elan->reset_gpio, 0);
+	if (ihid_elan->chip_data->post_gpio_reset_delay_ms)
+		msleep(ihid_elan->chip_data->post_gpio_reset_delay_ms);
+
+	return 0;
+}
+
+static void elan_i2c_hid_power_down(struct i2chid_ops *ops)
+{
+	struct i2c_hid_of_elan *ihid_elan =
+		container_of(ops, struct i2c_hid_of_elan, ops);
+
+	gpiod_set_value_cansleep(ihid_elan->reset_gpio, 1);
+	regulator_disable(ihid_elan->vccio);
+	regulator_disable(ihid_elan->vcc33);
+}
+
+static int i2c_hid_of_elan_probe(struct i2c_client *client,
+				 const struct i2c_device_id *id)
+{
+	struct i2c_hid_of_elan *ihid_elan;
+
+	ihid_elan = devm_kzalloc(&client->dev, sizeof(*ihid_elan), GFP_KERNEL);
+	if (!ihid_elan)
+		return -ENOMEM;
+
+	ihid_elan->ops.power_up = elan_i2c_hid_power_up;
+	ihid_elan->ops.power_down = elan_i2c_hid_power_down;
+
+	/* Start out with reset asserted */
+	ihid_elan->reset_gpio =
+		devm_gpiod_get_optional(&client->dev, "reset", GPIOD_OUT_HIGH);
+	if (IS_ERR(ihid_elan->reset_gpio))
+		return PTR_ERR(ihid_elan->reset_gpio);
+
+	ihid_elan->vccio = devm_regulator_get(&client->dev, "vccio");
+	if (IS_ERR(ihid_elan->vccio))
+		return PTR_ERR(ihid_elan->vccio);
+
+	ihid_elan->vcc33 = devm_regulator_get(&client->dev, "vcc33");
+	if (IS_ERR(ihid_elan->vcc33))
+		return PTR_ERR(ihid_elan->vcc33);
+
+	ihid_elan->chip_data = device_get_match_data(&client->dev);
+
+	return i2c_hid_core_probe(client, &ihid_elan->ops,
+				  ihid_elan->chip_data->hid_descriptor_address, 0);
+}
+
+static const struct elan_i2c_hid_chip_data elan_ekth6915_chip_data = {
+	.post_power_delay_ms = 1,
+	.post_gpio_reset_delay_ms = 300,
+	.hid_descriptor_address = 0x0001,
+};
+
+static const struct of_device_id elan_i2c_hid_of_match[] = {
+	{ .compatible = "elan,ekth6915", .data = &elan_ekth6915_chip_data },
+	{ }
+};
+MODULE_DEVICE_TABLE(of, elan_i2c_hid_of_match);
+
+static struct i2c_driver elan_i2c_hid_ts_driver = {
+	.driver = {
+		.name	= "i2c_hid_of_elan",
+		.pm	= &i2c_hid_core_pm,
+		.probe_type = PROBE_PREFER_ASYNCHRONOUS,
+		.of_match_table = of_match_ptr(elan_i2c_hid_of_match),
+	},
+	.probe		= i2c_hid_of_elan_probe,
+	.remove		= i2c_hid_core_remove,
+	.shutdown	= i2c_hid_core_shutdown,
+};
+module_i2c_driver(elan_i2c_hid_ts_driver);
+
+MODULE_AUTHOR("Douglas Anderson <dianders@chromium.org>");
+MODULE_DESCRIPTION("Elan i2c-hid touchscreen driver");
+MODULE_LICENSE("GPL");