// SPDX-License-Identifier: GPL-2.0-only
/*
 * UART interface for ChromeOS Embedded Controller
 *
 * Copyright 2020-2022 Google LLC.
 */

#include <linux/acpi.h>
#include <linux/delay.h>
#include <linux/errno.h>
#include <linux/init.h>
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/of.h>
#include <linux/platform_data/cros_ec_proto.h>
#include <linux/serdev.h>
#include <linux/slab.h>
#include <uapi/linux/sched/types.h>

#include "cros_ec.h"

/*
 * EC sends contiguous bytes of response packet on UART AP RX.
 * TTY driver in AP accumulates incoming bytes and calls the registered callback
 * function. Byte count can range from 1 to MAX bytes supported by EC.
 * This driver should wait for long time for all callbacks to be processed.
 * Considering the worst case scenario, wait for 500 msec. This timeout should
 * account for max latency and some additional guard time.
 * Best case: Entire packet is received in ~200 ms, wait queue will be released
 * and packet will be processed.
 * Worst case: TTY driver sends bytes in multiple callbacks. In this case this
 * driver will wait for ~1 sec beyond which it will timeout.
 * This timeout value should not exceed ~500 msec because in case if
 * EC_CMD_REBOOT_EC sent, high level driver should be able to intercept EC
 * in RO.
 */
#define EC_MSG_DEADLINE_MS              500

/**
 * struct response_info - Encapsulate EC response related
 *                      information for passing between function
 *                      cros_ec_uart_pkt_xfer() and cros_ec_uart_rx_bytes()
 *                      callback.
 * @data:               Copy the data received from EC here.
 * @max_size:           Max size allocated for the @data buffer. If the
 *                      received data exceeds this value, we log an error.
 * @size:               Actual size of data received from EC. This is also
 *                      used to accumulate byte count with response is received
 *                      in dma chunks.
 * @exp_len:            Expected bytes of response from EC including header.
 * @status:             Re-init to 0 before sending a cmd. Updated to 1 when
 *                      a response is successfully received, or an error number
 *                      on failure.
 * @wait_queue: Wait queue EC response where the cros_ec sends request
 *                      to EC and waits
 */
struct response_info {
        void *data;
        size_t max_size;
        size_t size;
        size_t exp_len;
        int status;
        wait_queue_head_t wait_queue;
};

/**
 * struct cros_ec_uart - information about a uart-connected EC
 *
 * @serdev:             serdev uart device we are connected to.
 * @baudrate:           UART baudrate of attached EC device.
 * @flowcontrol:        UART flowcontrol of attached device.
 * @irq:                Linux IRQ number of associated serial device.
 * @response:           Response info passing between cros_ec_uart_pkt_xfer()
 *                      and cros_ec_uart_rx_bytes()
 */
struct cros_ec_uart {
        struct serdev_device *serdev;
        u32 baudrate;
        u8 flowcontrol;
        u32 irq;
        struct response_info response;
};

static size_t cros_ec_uart_rx_bytes(struct serdev_device *serdev,
                                    const u8 *data, size_t count)
{
        struct ec_host_response *host_response;
        struct cros_ec_device *ec_dev = serdev_device_get_drvdata(serdev);
        struct cros_ec_uart *ec_uart = ec_dev->priv;
        struct response_info *resp = &ec_uart->response;

        /* Check if bytes were sent out of band */
        if (!resp->data) {
                /* Discard all bytes */
                dev_warn(ec_dev->dev, "Bytes received out of band, dropping them.\n");
                return count;
        }

        /*
         * Check if incoming bytes + resp->size is greater than allocated
         * buffer in din by cros_ec. This will ensure that if EC sends more
         * bytes than max_size, waiting process will be notified with an error.
         */
        if (resp->size + count > resp->max_size) {
                resp->status = -EMSGSIZE;
                wake_up(&resp->wait_queue);
                return count;
        }

        memcpy(resp->data + resp->size, data, count);

        resp->size += count;

        /* Read data_len if we received response header and if exp_len was not read before. */
        if (resp->size >= sizeof(*host_response) && resp->exp_len == 0) {
                host_response = (struct ec_host_response *)resp->data;
                resp->exp_len = host_response->data_len + sizeof(*host_response);
        }

        /* If driver received response header and payload from EC, wake up the wait queue. */
        if (resp->size >= sizeof(*host_response) && resp->size == resp->exp_len) {
                resp->status = 1;
                wake_up(&resp->wait_queue);
        }

        return count;
}

static int cros_ec_uart_pkt_xfer(struct cros_ec_device *ec_dev,
                                 struct cros_ec_command *ec_msg)
{
        struct cros_ec_uart *ec_uart = ec_dev->priv;
        struct serdev_device *serdev = ec_uart->serdev;
        struct response_info *resp = &ec_uart->response;
        struct ec_host_response *host_response;
        unsigned int len;
        int ret, i;
        u8 sum;

        len = cros_ec_prepare_tx(ec_dev, ec_msg);
        dev_dbg(ec_dev->dev, "Prepared len=%d\n", len);

        /* Setup for incoming response */
        resp->data = ec_dev->din;
        resp->max_size = ec_dev->din_size;
        resp->size = 0;
        resp->exp_len = 0;
        resp->status = 0;

        ret = serdev_device_write_buf(serdev, ec_dev->dout, len);
        if (ret < 0 || ret < len) {
                dev_err(ec_dev->dev, "Unable to write data\n");
                if (ret >= 0)
                        ret = -EIO;
                goto exit;
        }

        ret = wait_event_timeout(resp->wait_queue, resp->status,
                                 msecs_to_jiffies(EC_MSG_DEADLINE_MS));
        if (ret == 0) {
                dev_warn(ec_dev->dev, "Timed out waiting for response.\n");
                ret = -ETIMEDOUT;
                goto exit;
        }

        if (resp->status < 0) {
                ret = resp->status;
                dev_warn(ec_dev->dev, "Error response received: %d\n", ret);
                goto exit;
        }

        host_response = (struct ec_host_response *)ec_dev->din;
        ec_msg->result = host_response->result;

        if (host_response->data_len > ec_msg->insize) {
                dev_err(ec_dev->dev, "Resp too long (%d bytes, expected %d)\n",
                        host_response->data_len, ec_msg->insize);
                ret = -ENOSPC;
                goto exit;
        }

        /* Validate checksum */
        sum = 0;
        for (i = 0; i < sizeof(*host_response) + host_response->data_len; i++)
                sum += ec_dev->din[i];

        if (sum) {
                dev_err(ec_dev->dev, "Bad packet checksum calculated %x\n", sum);
                ret = -EBADMSG;
                goto exit;
        }

        memcpy(ec_msg->data, ec_dev->din + sizeof(*host_response), host_response->data_len);

        ret = host_response->data_len;

exit:
        /* Invalidate response buffer to guard against out of band rx data */
        resp->data = NULL;

        if (ec_msg->command == EC_CMD_REBOOT_EC)
                msleep(EC_REBOOT_DELAY_MS);

        return ret;
}

static int cros_ec_uart_resource(struct acpi_resource *ares, void *data)
{
        struct cros_ec_uart *ec_uart = data;
        struct acpi_resource_uart_serialbus *sb = &ares->data.uart_serial_bus;

        if (ares->type == ACPI_RESOURCE_TYPE_SERIAL_BUS &&
            sb->type == ACPI_RESOURCE_SERIAL_TYPE_UART) {
                ec_uart->baudrate = sb->default_baud_rate;
                dev_dbg(&ec_uart->serdev->dev, "Baudrate %d\n", ec_uart->baudrate);

                ec_uart->flowcontrol = sb->flow_control;
                dev_dbg(&ec_uart->serdev->dev, "Flow control %d\n", ec_uart->flowcontrol);
        }

        return 0;
}

static int cros_ec_uart_acpi_probe(struct cros_ec_uart *ec_uart)
{
        int ret;
        LIST_HEAD(resources);
        struct acpi_device *adev = ACPI_COMPANION(&ec_uart->serdev->dev);

        ret = acpi_dev_get_resources(adev, &resources, cros_ec_uart_resource, ec_uart);
        if (ret < 0)
                return ret;

        acpi_dev_free_resource_list(&resources);

        /* Retrieve GpioInt and translate it to Linux IRQ number */
        ret = acpi_dev_gpio_irq_get(adev, 0);
        if (ret < 0)
                return ret;

        ec_uart->irq = ret;
        dev_dbg(&ec_uart->serdev->dev, "IRQ number %d\n", ec_uart->irq);

        return 0;
}

static const struct serdev_device_ops cros_ec_uart_client_ops = {
        .receive_buf = cros_ec_uart_rx_bytes,
};

static int cros_ec_uart_probe(struct serdev_device *serdev)
{
        struct device *dev = &serdev->dev;
        struct cros_ec_device *ec_dev;
        struct cros_ec_uart *ec_uart;
        int ret;

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

        ec_dev = cros_ec_device_alloc(dev);
        if (!ec_dev)
                return -ENOMEM;

        serdev_device_set_drvdata(serdev, ec_dev);
        init_waitqueue_head(&ec_uart->response.wait_queue);

        ec_uart->serdev = serdev;

        ret = cros_ec_uart_acpi_probe(ec_uart);
        if (ret < 0) {
                dev_err(dev, "Failed to get ACPI info (%d)", ret);
                return ret;
        }

        /* Initialize ec_dev for cros_ec  */
        ec_dev->phys_name = dev_name(dev);
        ec_dev->priv = ec_uart;
        ec_dev->irq = ec_uart->irq;
        ec_dev->cmd_xfer = NULL;
        ec_dev->pkt_xfer = cros_ec_uart_pkt_xfer;

        serdev_device_set_client_ops(serdev, &cros_ec_uart_client_ops);

        ret = devm_serdev_device_open(dev, serdev);
        if (ret) {
                dev_err(dev, "Unable to open UART device");
                return ret;
        }

        ret = serdev_device_set_baudrate(serdev, ec_uart->baudrate);
        if (ret < 0) {
                dev_err(dev, "Failed to set up host baud rate (%d)", ret);
                return ret;
        }

        serdev_device_set_flow_control(serdev, ec_uart->flowcontrol);

        return cros_ec_register(ec_dev);
}

static void cros_ec_uart_remove(struct serdev_device *serdev)
{
        struct cros_ec_device *ec_dev = serdev_device_get_drvdata(serdev);

        cros_ec_unregister(ec_dev);
};

static int __maybe_unused cros_ec_uart_suspend(struct device *dev)
{
        struct cros_ec_device *ec_dev = dev_get_drvdata(dev);

        return cros_ec_suspend(ec_dev);
}

static int __maybe_unused cros_ec_uart_resume(struct device *dev)
{
        struct cros_ec_device *ec_dev = dev_get_drvdata(dev);

        return cros_ec_resume(ec_dev);
}

static SIMPLE_DEV_PM_OPS(cros_ec_uart_pm_ops, cros_ec_uart_suspend,
                         cros_ec_uart_resume);

static const struct of_device_id cros_ec_uart_of_match[] = {
        { .compatible = "google,cros-ec-uart" },
        {}
};
MODULE_DEVICE_TABLE(of, cros_ec_uart_of_match);

#ifdef CONFIG_ACPI
static const struct acpi_device_id cros_ec_uart_acpi_id[] = {
        { "GOOG0019", 0 },
        {}
};

MODULE_DEVICE_TABLE(acpi, cros_ec_uart_acpi_id);
#endif

static struct serdev_device_driver cros_ec_uart_driver = {
        .driver = {
                .name   = "cros-ec-uart",
                .acpi_match_table = ACPI_PTR(cros_ec_uart_acpi_id),
                .of_match_table = cros_ec_uart_of_match,
                .pm     = &cros_ec_uart_pm_ops,
        },
        .probe          = cros_ec_uart_probe,
        .remove         = cros_ec_uart_remove,
};

module_serdev_device_driver(cros_ec_uart_driver);

MODULE_LICENSE("GPL");
MODULE_DESCRIPTION("UART interface for ChromeOS Embedded Controller");
MODULE_AUTHOR("Bhanu Prakash Maiya <bhanumaiya@chromium.org>");