Input: novatek-nvt-ts - support being panel follower

Sometimes Novatek touchscreen is paired together with Novatek panel,
and they both need to be powered together in sync.

Add support for nvt-ts driver to operate in panel follower mode, in
which touchscreen isn't in full control of its lifecycle.
This is managed using callbacks from panel, to get informed when the
panel is powered on and off. From there we can match the nvt-ts
device's power state to that of the panel.

Without this probing touchscreen before panel sometimes randomly fails
with I2C read errors.

 * split some code from probe function to separate initial_power_on
   function, which is called once from panel_prepared callback, or
   from probe function, depending on mode;
 * update Kconfig to depend on DRM.

Signed-off-by: Alexey Minnekhanov <alexeymin@postmarketos.org>

Author: minlexx

drivers/input/touchscreen/Kconfig

@@ -660,7 +660,7 @@ config TOUCHSCREEN_MTOUCH
 
 config TOUCHSCREEN_NOVATEK_NVT_TS
 	tristate "Novatek NT11205 touchscreen support"
-	depends on I2C
+	depends on I2C && (DRM || !DRM)
 	help
 	  Say Y here if you have a Novatek NT11205 touchscreen.
 	  If unsure, say N.

drivers/input/touchscreen/novatek-nvt-ts.c

@@ -6,6 +6,7 @@
  * Copyright (c) 2023 Hans de Goede <hdegoede@redhat.com>
  */
 
+#include <drm/drm_panel.h>
 #include <linux/delay.h>
 #include <linux/gpio/consumer.h>
 #include <linux/interrupt.h>
@@ -14,7 +15,6 @@
 #include <linux/input/mt.h>
 #include <linux/input/touchscreen.h>
 #include <linux/module.h>
-
 #include <linux/unaligned.h>
 
 #define NVT_TS_TOUCH_START		0x00
@@ -61,6 +61,12 @@ struct nvt_ts_data {
 	struct touchscreen_properties prop;
 	int max_touches;
 	u8 buf[NVT_TS_TOUCH_SIZE * NVT_TS_MAX_TOUCHES];
+	/*
+	 * Sometimes Novatek touchscreen is paired together with Novatek panel,
+	 * and they need to be powered together in sync.
+	 */
+	struct drm_panel_follower panel_follower;
+	bool is_panel_follower;
 };
 
 static int nvt_ts_read_data(struct i2c_client *client, u8 reg, u8 *data, int count)
@@ -97,6 +103,9 @@ static irqreturn_t nvt_ts_irq(int irq, void *dev_id)
 	bool active;
 	u8 *touch;
 
+	if (!data->input)
+		return IRQ_HANDLED;
+
 	error = nvt_ts_read_data(data->client, NVT_TS_TOUCH_START, data->buf,
 				 data->max_touches * NVT_TS_TOUCH_SIZE);
 	if (error)
@@ -155,6 +164,7 @@ static int nvt_ts_start(struct input_dev *dev)
 
 	enable_irq(data->client->irq);
 	gpiod_set_value_cansleep(data->reset_gpio, 0);
+	msleep(100); // TODO: is it really needed? probably
 
 	return 0;
 }
@@ -172,6 +182,9 @@ static int nvt_ts_suspend(struct device *dev)
 {
 	struct nvt_ts_data *data = i2c_get_clientdata(to_i2c_client(dev));
 
+	if (data->is_panel_follower)
+		return 0;
+
 	mutex_lock(&data->input->mutex);
 	if (input_device_enabled(data->input))
 		nvt_ts_stop(data->input);
@@ -184,6 +197,9 @@ static int nvt_ts_resume(struct device *dev)
 {
 	struct nvt_ts_data *data = i2c_get_clientdata(to_i2c_client(dev));
 
+	if (data->is_panel_follower)
+		return 0;
+
 	mutex_lock(&data->input->mutex);
 	if (input_device_enabled(data->input))
 		nvt_ts_start(data->input);
@@ -192,32 +208,17 @@ static int nvt_ts_resume(struct device *dev)
 	return 0;
 }
 
-static DEFINE_SIMPLE_DEV_PM_OPS(nvt_ts_pm_ops, nvt_ts_suspend, nvt_ts_resume);
-
-static int nvt_ts_probe(struct i2c_client *client)
+static int nvt_ts_initial_power_on_and_register_inputdev(struct nvt_ts_data *data)
 {
-	struct device *dev = &client->dev;
+	struct device *dev = &data->client->dev;
 	int error, width, height, irq_type;
-	struct nvt_ts_data *data;
 	const struct nvt_ts_i2c_chip_data *chip;
 	struct input_dev *input;
 
-	if (!client->irq) {
-		dev_err(dev, "Error no irq specified\n");
-		return -EINVAL;
-	}
-
-	data = devm_kzalloc(dev, sizeof(*data), GFP_KERNEL);
-	if (!data)
-		return -ENOMEM;
-
-	chip = device_get_match_data(&client->dev);
+	chip = device_get_match_data(dev);
 	if (!chip)
 		return -EINVAL;
 
-	data->client = client;
-	i2c_set_clientdata(client, data);
-
 	/*
 	 * VCC is the analog voltage supply
 	 * IOVCC is the digital voltage supply
@@ -278,7 +279,7 @@ static int nvt_ts_probe(struct i2c_client *client)
 	if (!input)
 		return -ENOMEM;
 
-	input->name = client->name;
+	input->name = data->client->name;
 	input->id.bustype = BUS_I2C;
 	input->open = nvt_ts_start;
 	input->close = nvt_ts_stop;
@@ -295,10 +296,11 @@ static int nvt_ts_probe(struct i2c_client *client)
 	data->input = input;
 	input_set_drvdata(input, data);
 
-	error = devm_request_threaded_irq(dev, client->irq, NULL, nvt_ts_irq,
+	error = devm_request_threaded_irq(dev, data->client->irq, NULL,
+					  nvt_ts_irq,
 					  IRQF_ONESHOT | IRQF_NO_AUTOEN |
 						nvt_ts_irq_type[irq_type],
-					  client->name, data);
+					  data->client->name, data);
 	if (error) {
 		dev_err(dev, "failed to request irq: %d\n", error);
 		return error;
@@ -313,6 +315,91 @@ static int nvt_ts_probe(struct i2c_client *client)
 	return 0;
 }
 
+static int on_novatek_panel_prepared(struct drm_panel_follower *follower)
+{
+	struct nvt_ts_data *data = container_of(follower, struct nvt_ts_data, panel_follower);
+	int ret;
+	dev_info(&data->client->dev, "%s\n", __func__); // REMOVEME
+
+	/* Is this the first power on? */
+	if (!data->input) {
+		dev_info(&data->client->dev, "doing initial power on\n"); // REMOVEME
+		ret = nvt_ts_initial_power_on_and_register_inputdev(data);
+		if (ret)
+			return ret;
+	}
+
+	mutex_lock(&data->input->mutex);
+	if (input_device_enabled(data->input))
+		nvt_ts_start(data->input);
+	mutex_unlock(&data->input->mutex);
+
+	return 0;
+}
+
+static int on_novatek_panel_unpreparing(struct drm_panel_follower *follower)
+{
+	struct nvt_ts_data *data = container_of(follower, struct nvt_ts_data, panel_follower);
+	dev_info(&data->client->dev, "%s\n", __func__); // REMOVEME
+
+	mutex_lock(&data->input->mutex);
+	if (input_device_enabled(data->input))
+		nvt_ts_stop(data->input);
+	mutex_unlock(&data->input->mutex);
+
+	return 0;
+}
+
+static const struct drm_panel_follower_funcs nvt_ts_follower_funcs = {
+	.panel_prepared = on_novatek_panel_prepared,
+	.panel_unpreparing = on_novatek_panel_unpreparing,
+};
+
+static DEFINE_SIMPLE_DEV_PM_OPS(nvt_ts_pm_ops, nvt_ts_suspend, nvt_ts_resume);
+
+static int nvt_ts_probe(struct i2c_client *client)
+{
+	struct device *dev = &client->dev;
+	struct nvt_ts_data *data;
+
+	if (!client->irq) {
+		dev_err(dev, "Error no irq specified\n");
+		return -EINVAL;
+	}
+
+	data = devm_kzalloc(dev, sizeof(*data), GFP_KERNEL);
+	if (!data)
+		return -ENOMEM;
+
+	data->client = client;
+	i2c_set_clientdata(client, data);
+
+	/* check if "panel = <&...>" is set in DT */
+	if (drm_is_panel_follower(dev)) {
+		/* register self as follower */
+		dev_info(dev, "probing in follower mode\n"); // REMOVEME
+		data->is_panel_follower = true;
+		data->panel_follower.funcs = &nvt_ts_follower_funcs;
+		drm_panel_add_follower(dev, &data->panel_follower);
+		/*
+		 * In this mode, we can't do anything more at this moment.
+		 * Need to wait for callbacks from panel.
+		 */
+		return 0;
+	}
+
+	dev_info(dev, "probing in normal mode\n"); // REMOVEME
+	return nvt_ts_initial_power_on_and_register_inputdev(data);
+}
+
+static void nvt_ts_remove(struct i2c_client *client)
+{
+	struct nvt_ts_data *data = i2c_get_clientdata(client);
+
+	if (data->is_panel_follower)
+		drm_panel_remove_follower(&data->panel_follower);
+}
+
 static const struct nvt_ts_i2c_chip_data nvt_nt11205_ts_data = {
 	.wake_type = 0x05,
 	.chip_id = 0x05,
@@ -344,6 +431,7 @@ static struct i2c_driver nvt_ts_driver = {
 		.of_match_table = nvt_ts_of_match,
 	},
 	.probe = nvt_ts_probe,
+	.remove = nvt_ts_remove,
 	.id_table = nvt_ts_i2c_id,
 };