// SPDX-License-Identifier: GPL-2.0-or-later
/*
 * Support for the custom fast charging protocol found on the Lenovo Yoga
 * Tablet 2 1380F / 1380L models.
 *
 * Copyright (C) 2024 Hans de Goede <hansg@kernel.org>
 */
#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

#include <linux/delay.h>
#include <linux/err.h>
#include <linux/errno.h>
#include <linux/extcon.h>
#include <linux/gpio/consumer.h>
#include <linux/module.h>
#include <linux/notifier.h>
#include <linux/pinctrl/consumer.h>
#include <linux/pinctrl/machine.h>
#include <linux/platform_device.h>
#include <linux/serdev.h>
#include <linux/time.h>
#include <linux/types.h>
#include <linux/workqueue.h>
#include "serdev_helpers.h"

#define YT2_1380_FC_PDEV_NAME		"lenovo-yoga-tab2-pro-1380-fastcharger"
#define YT2_1380_FC_SERDEV_CTRL		"serial0"
#define YT2_1380_FC_SERDEV_NAME		"serial0-0"
#define YT2_1380_FC_EXTCON_NAME		"i2c-lc824206xa"

#define YT2_1380_FC_MAX_TRIES		5
#define YT2_1380_FC_PIN_SW_DELAY_US	(10 * USEC_PER_MSEC)
#define YT2_1380_FC_UART_DRAIN_DELAY_US	(50 * USEC_PER_MSEC)
#define YT2_1380_FC_VOLT_SW_DELAY_US	(1000 * USEC_PER_MSEC)

struct yt2_1380_fc {
	struct device *dev;
	struct pinctrl *pinctrl;
	struct pinctrl_state *gpio_state;
	struct pinctrl_state *uart_state;
	struct gpio_desc *uart3_txd;
	struct gpio_desc *uart3_rxd;
	struct extcon_dev *extcon;
	struct notifier_block nb;
	struct work_struct work;
	bool fast_charging;
};

static int yt2_1380_fc_set_gpio_mode(struct yt2_1380_fc *fc, bool enable)
{
	struct pinctrl_state *state = enable ? fc->gpio_state : fc->uart_state;
	int ret;

	ret = pinctrl_select_state(fc->pinctrl, state);
	if (ret) {
		dev_err(fc->dev, "Error %d setting pinctrl state\n", ret);
		return ret;
	}

	fsleep(YT2_1380_FC_PIN_SW_DELAY_US);
	return 0;
}

static bool yt2_1380_fc_dedicated_charger_connected(struct yt2_1380_fc *fc)
{
	return extcon_get_state(fc->extcon, EXTCON_CHG_USB_DCP) > 0;
}

static bool yt2_1380_fc_fast_charger_connected(struct yt2_1380_fc *fc)
{
	return extcon_get_state(fc->extcon, EXTCON_CHG_USB_FAST) > 0;
}

static void yt2_1380_fc_worker(struct work_struct *work)
{
	struct yt2_1380_fc *fc = container_of(work, struct yt2_1380_fc, work);
	int i, ret;

	/* Do nothing if already fast charging */
	if (yt2_1380_fc_fast_charger_connected(fc))
		return;

	for (i = 0; i < YT2_1380_FC_MAX_TRIES; i++) {
		/* Set pins to UART mode (for charger disconnect and retries) */
		ret = yt2_1380_fc_set_gpio_mode(fc, false);
		if (ret)
			return;

		/* Only try 12V charging if a dedicated charger is detected */
		if (!yt2_1380_fc_dedicated_charger_connected(fc))
			return;

		/* Send the command to switch to 12V charging */
		ret = serdev_device_write_buf(to_serdev_device(fc->dev), "SC", strlen("SC"));
		if (ret != strlen("SC")) {
			dev_err(fc->dev, "Error %d writing to uart\n", ret);
			return;
		}

		fsleep(YT2_1380_FC_UART_DRAIN_DELAY_US);

		/* Re-check a charger is still connected */
		if (!yt2_1380_fc_dedicated_charger_connected(fc))
			return;

		/*
		 * Now switch the lines to GPIO (output, high). The charger
		 * expects the lines being driven high after the command.
		 * Presumably this is used to detect the tablet getting
		 * unplugged (to switch back to 5V output on unplug).
		 */
		ret = yt2_1380_fc_set_gpio_mode(fc, true);
		if (ret)
			return;

		fsleep(YT2_1380_FC_VOLT_SW_DELAY_US);

		if (yt2_1380_fc_fast_charger_connected(fc))
			return; /* Success */
	}

	dev_dbg(fc->dev, "Failed to switch to 12V charging (not the original charger?)\n");
	/* Failed to enable 12V fast charging, reset pins to default UART mode */
	yt2_1380_fc_set_gpio_mode(fc, false);
}

static int yt2_1380_fc_extcon_evt(struct notifier_block *nb,
				  unsigned long event, void *param)
{
	struct yt2_1380_fc *fc = container_of(nb, struct yt2_1380_fc, nb);

	schedule_work(&fc->work);
	return NOTIFY_OK;
}

static size_t yt2_1380_fc_receive(struct serdev_device *serdev, const u8 *data, size_t len)
{
	/*
	 * Since the USB data lines are shorted for DCP detection, echos of
	 * the "SC" command send in yt2_1380_fc_worker() will be received.
	 */
	dev_dbg(&serdev->dev, "recv: %*ph\n", (int)len, data);
	return len;
}

static const struct serdev_device_ops yt2_1380_fc_serdev_ops = {
	.receive_buf = yt2_1380_fc_receive,
	.write_wakeup = serdev_device_write_wakeup,
};

static int yt2_1380_fc_serdev_probe(struct serdev_device *serdev)
{
	struct device *dev = &serdev->dev;
	struct yt2_1380_fc *fc;
	int ret;

	fc = devm_kzalloc(dev, sizeof(*fc), GFP_KERNEL);
	if (!fc)
		return -ENOMEM;

	fc->dev = dev;
	fc->nb.notifier_call = yt2_1380_fc_extcon_evt;
	INIT_WORK(&fc->work, yt2_1380_fc_worker);

	/*
	 * Do this first since it may return -EPROBE_DEFER.
	 * There is no extcon_put(), so there is no need to free this.
	 */
	fc->extcon = extcon_get_extcon_dev(YT2_1380_FC_EXTCON_NAME);
	if (IS_ERR(fc->extcon))
		return dev_err_probe(dev, PTR_ERR(fc->extcon), "getting extcon\n");

	fc->pinctrl = devm_pinctrl_get(dev);
	if (IS_ERR(fc->pinctrl))
		return dev_err_probe(dev, PTR_ERR(fc->pinctrl), "getting pinctrl\n");

	/*
	 * To switch the UART3 pins connected to the USB data lines between
	 * UART and GPIO modes.
	 */
	fc->gpio_state = pinctrl_lookup_state(fc->pinctrl, "uart3_gpio");
	fc->uart_state = pinctrl_lookup_state(fc->pinctrl, "uart3_uart");
	if (IS_ERR(fc->gpio_state) || IS_ERR(fc->uart_state))
		return dev_err_probe(dev, -EINVAL, "getting pinctrl states\n");

	ret = yt2_1380_fc_set_gpio_mode(fc, true);
	if (ret)
		return ret;

	fc->uart3_txd = devm_gpiod_get(dev, "uart3_txd", GPIOD_OUT_HIGH);
	if (IS_ERR(fc->uart3_txd))
		return dev_err_probe(dev, PTR_ERR(fc->uart3_txd), "getting uart3_txd gpio\n");

	fc->uart3_rxd = devm_gpiod_get(dev, "uart3_rxd", GPIOD_OUT_HIGH);
	if (IS_ERR(fc->uart3_rxd))
		return dev_err_probe(dev, PTR_ERR(fc->uart3_rxd), "getting uart3_rxd gpio\n");

	ret = yt2_1380_fc_set_gpio_mode(fc, false);
	if (ret)
		return ret;

	ret = devm_serdev_device_open(dev, serdev);
	if (ret)
		return dev_err_probe(dev, ret, "opening UART device\n");

	serdev_device_set_baudrate(serdev, 600);
	serdev_device_set_flow_control(serdev, false);
	serdev_device_set_drvdata(serdev, fc);
	serdev_device_set_client_ops(serdev, &yt2_1380_fc_serdev_ops);

	ret = devm_extcon_register_notifier_all(dev, fc->extcon, &fc->nb);
	if (ret)
		return dev_err_probe(dev, ret, "registering extcon notifier\n");

	/* In case the extcon already has detected a DCP charger */
	schedule_work(&fc->work);

	return 0;
}

struct serdev_device_driver yt2_1380_fc_serdev_driver = {
	.probe = yt2_1380_fc_serdev_probe,
	.driver = {
		.name = KBUILD_MODNAME,
	},
};

static const struct pinctrl_map yt2_1380_fc_pinctrl_map[] = {
	PIN_MAP_MUX_GROUP(YT2_1380_FC_SERDEV_NAME, "uart3_uart",
			  "INT33FC:00", "uart3_grp", "uart"),
	PIN_MAP_MUX_GROUP(YT2_1380_FC_SERDEV_NAME, "uart3_gpio",
			  "INT33FC:00", "uart3_grp_gpio", "gpio"),
};

static int yt2_1380_fc_pdev_probe(struct platform_device *pdev)
{
	struct serdev_device *serdev;
	struct device *ctrl_dev;
	int ret;

	/* Register pinctrl mappings for setting the UART3 pins mode */
	ret = pinctrl_register_mappings(yt2_1380_fc_pinctrl_map,
					ARRAY_SIZE(yt2_1380_fc_pinctrl_map));
	if (ret)
		return ret;

	/* And create the serdev to talk to the charger over the UART3 pins */
	ctrl_dev = get_serdev_controller("PNP0501", "1", 0, YT2_1380_FC_SERDEV_CTRL);
	if (IS_ERR(ctrl_dev)) {
		ret = PTR_ERR(ctrl_dev);
		goto out_pinctrl_unregister_mappings;
	}

	serdev = serdev_device_alloc(to_serdev_controller(ctrl_dev));
	put_device(ctrl_dev);
	if (!serdev) {
		ret = -ENOMEM;
		goto out_pinctrl_unregister_mappings;
	}

	ret = serdev_device_add(serdev);
	if (ret) {
		dev_err_probe(&pdev->dev, ret, "adding serdev\n");
		serdev_device_put(serdev);
		goto out_pinctrl_unregister_mappings;
	}

	/*
	 * serdev device <-> driver matching relies on OF or ACPI matches and
	 * neither is available here, manually bind the driver.
	 */
	ret = device_driver_attach(&yt2_1380_fc_serdev_driver.driver, &serdev->dev);
	if (ret) {
		/* device_driver_attach() maps EPROBE_DEFER to EAGAIN, map it back */
		ret = (ret == -EAGAIN) ? -EPROBE_DEFER : ret;
		dev_err_probe(&pdev->dev, ret, "attaching serdev driver\n");
		goto out_serdev_device_remove;
	}

	/* So that yt2_1380_fc_pdev_remove() can remove the serdev */
	platform_set_drvdata(pdev, serdev);
	return 0;

out_serdev_device_remove:
	serdev_device_remove(serdev);
out_pinctrl_unregister_mappings:
	pinctrl_unregister_mappings(yt2_1380_fc_pinctrl_map);
	return ret;
}

static void yt2_1380_fc_pdev_remove(struct platform_device *pdev)
{
	struct serdev_device *serdev = platform_get_drvdata(pdev);

	serdev_device_remove(serdev);
	pinctrl_unregister_mappings(yt2_1380_fc_pinctrl_map);
}

static struct platform_driver yt2_1380_fc_pdev_driver = {
	.probe = yt2_1380_fc_pdev_probe,
	.remove = yt2_1380_fc_pdev_remove,
	.driver = {
		.name = YT2_1380_FC_PDEV_NAME,
		.probe_type = PROBE_PREFER_ASYNCHRONOUS,
	},
};

static int __init yt2_1380_fc_module_init(void)
{
	int ret;

	/*
	 * serdev driver MUST be registered first because pdev driver calls
	 * device_driver_attach() on the serdev, serdev-driver pair.
	 */
	ret = serdev_device_driver_register(&yt2_1380_fc_serdev_driver);
	if (ret)
		return ret;

	ret = platform_driver_register(&yt2_1380_fc_pdev_driver);
	if (ret)
		serdev_device_driver_unregister(&yt2_1380_fc_serdev_driver);

	return ret;
}
module_init(yt2_1380_fc_module_init);

static void __exit yt2_1380_fc_module_exit(void)
{
	platform_driver_unregister(&yt2_1380_fc_pdev_driver);
	serdev_device_driver_unregister(&yt2_1380_fc_serdev_driver);
}
module_exit(yt2_1380_fc_module_exit);

MODULE_ALIAS("platform:" YT2_1380_FC_PDEV_NAME);
MODULE_DESCRIPTION("Lenovo Yoga Tablet 2 1380 fast charge driver");
MODULE_AUTHOR("Hans de Goede <hansg@kernel.org>");
MODULE_LICENSE("GPL");