// SPDX-License-Identifier: GPL-2.0
/*
 * LiteUART serial controller (LiteX) Driver
 *
 * Copyright (C) 2019-2020 Antmicro <www.antmicro.com>
 */

#include <linux/console.h>
#include <linux/litex.h>
#include <linux/module.h>
#include <linux/of.h>
#include <linux/of_address.h>
#include <linux/of_platform.h>
#include <linux/serial.h>
#include <linux/serial_core.h>
#include <linux/slab.h>
#include <linux/timer.h>
#include <linux/tty_flip.h>
#include <linux/xarray.h>

/*
 * CSRs definitions (base address offsets + width)
 *
 * The definitions below are true for LiteX SoC configured for 8-bit CSR Bus,
 * 32-bit aligned.
 *
 * Supporting other configurations might require new definitions or a more
 * generic way of indexing the LiteX CSRs.
 *
 * For more details on how CSRs are defined and handled in LiteX, see comments
 * in the LiteX SoC Driver: drivers/soc/litex/litex_soc_ctrl.c
 */
#define OFF_RXTX        0x00
#define OFF_TXFULL      0x04
#define OFF_RXEMPTY     0x08
#define OFF_EV_STATUS   0x0c
#define OFF_EV_PENDING  0x10
#define OFF_EV_ENABLE   0x14

/* events */
#define EV_TX           0x1
#define EV_RX           0x2

struct liteuart_port {
        struct uart_port port;
        struct timer_list timer;
        u32 id;
};

#define to_liteuart_port(port)  container_of(port, struct liteuart_port, port)

static DEFINE_XARRAY_FLAGS(liteuart_array, XA_FLAGS_ALLOC);

#ifdef CONFIG_SERIAL_LITEUART_CONSOLE
static struct console liteuart_console;
#endif

static struct uart_driver liteuart_driver = {
        .owner = THIS_MODULE,
        .driver_name = "liteuart",
        .dev_name = "ttyLXU",
        .major = 0,
        .minor = 0,
        .nr = CONFIG_SERIAL_LITEUART_MAX_PORTS,
#ifdef CONFIG_SERIAL_LITEUART_CONSOLE
        .cons = &liteuart_console,
#endif
};

static void liteuart_timer(struct timer_list *t)
{
        struct liteuart_port *uart = from_timer(uart, t, timer);
        struct uart_port *port = &uart->port;
        unsigned char __iomem *membase = port->membase;
        unsigned int flg = TTY_NORMAL;
        int ch;
        unsigned long status;

        while ((status = !litex_read8(membase + OFF_RXEMPTY)) == 1) {
                ch = litex_read8(membase + OFF_RXTX);
                port->icount.rx++;

                /* necessary for RXEMPTY to refresh its value */
                litex_write8(membase + OFF_EV_PENDING, EV_TX | EV_RX);

                /* no overflow bits in status */
                if (!(uart_handle_sysrq_char(port, ch)))
                        uart_insert_char(port, status, 0, ch, flg);

                tty_flip_buffer_push(&port->state->port);
        }

        mod_timer(&uart->timer, jiffies + uart_poll_timeout(port));
}

static void liteuart_putchar(struct uart_port *port, int ch)
{
        while (litex_read8(port->membase + OFF_TXFULL))
                cpu_relax();

        litex_write8(port->membase + OFF_RXTX, ch);
}

static unsigned int liteuart_tx_empty(struct uart_port *port)
{
        /* not really tx empty, just checking if tx is not full */
        if (!litex_read8(port->membase + OFF_TXFULL))
                return TIOCSER_TEMT;

        return 0;
}

static void liteuart_set_mctrl(struct uart_port *port, unsigned int mctrl)
{
        /* modem control register is not present in LiteUART */
}

static unsigned int liteuart_get_mctrl(struct uart_port *port)
{
        return TIOCM_CTS | TIOCM_DSR | TIOCM_CAR;
}

static void liteuart_stop_tx(struct uart_port *port)
{
}

static void liteuart_start_tx(struct uart_port *port)
{
        struct circ_buf *xmit = &port->state->xmit;
        unsigned char ch;

        if (unlikely(port->x_char)) {
                litex_write8(port->membase + OFF_RXTX, port->x_char);
                port->icount.tx++;
                port->x_char = 0;
        } else if (!uart_circ_empty(xmit)) {
                while (xmit->head != xmit->tail) {
                        ch = xmit->buf[xmit->tail];
                        xmit->tail = (xmit->tail + 1) & (UART_XMIT_SIZE - 1);
                        port->icount.tx++;
                        liteuart_putchar(port, ch);
                }
        }

        if (uart_circ_chars_pending(xmit) < WAKEUP_CHARS)
                uart_write_wakeup(port);
}

static void liteuart_stop_rx(struct uart_port *port)
{
        struct liteuart_port *uart = to_liteuart_port(port);

        /* just delete timer */
        del_timer(&uart->timer);
}

static void liteuart_break_ctl(struct uart_port *port, int break_state)
{
        /* LiteUART doesn't support sending break signal */
}

static int liteuart_startup(struct uart_port *port)
{
        struct liteuart_port *uart = to_liteuart_port(port);

        /* disable events */
        litex_write8(port->membase + OFF_EV_ENABLE, 0);

        /* prepare timer for polling */
        timer_setup(&uart->timer, liteuart_timer, 0);
        mod_timer(&uart->timer, jiffies + uart_poll_timeout(port));

        return 0;
}

static void liteuart_shutdown(struct uart_port *port)
{
}

static void liteuart_set_termios(struct uart_port *port, struct ktermios *new,
                                 struct ktermios *old)
{
        unsigned int baud;
        unsigned long flags;

        spin_lock_irqsave(&port->lock, flags);

        /* update baudrate */
        baud = uart_get_baud_rate(port, new, old, 0, 460800);
        uart_update_timeout(port, new->c_cflag, baud);

        spin_unlock_irqrestore(&port->lock, flags);
}

static const char *liteuart_type(struct uart_port *port)
{
        return "liteuart";
}

static void liteuart_release_port(struct uart_port *port)
{
}

static int liteuart_request_port(struct uart_port *port)
{
        return 0;
}

static void liteuart_config_port(struct uart_port *port, int flags)
{
        /*
         * Driver core for serial ports forces a non-zero value for port type.
         * Write an arbitrary value here to accommodate the serial core driver,
         * as ID part of UAPI is redundant.
         */
        port->type = 1;
}

static int liteuart_verify_port(struct uart_port *port,
                                struct serial_struct *ser)
{
        if (port->type != PORT_UNKNOWN && ser->type != 1)
                return -EINVAL;

        return 0;
}

static const struct uart_ops liteuart_ops = {
        .tx_empty       = liteuart_tx_empty,
        .set_mctrl      = liteuart_set_mctrl,
        .get_mctrl      = liteuart_get_mctrl,
        .stop_tx        = liteuart_stop_tx,
        .start_tx       = liteuart_start_tx,
        .stop_rx        = liteuart_stop_rx,
        .break_ctl      = liteuart_break_ctl,
        .startup        = liteuart_startup,
        .shutdown       = liteuart_shutdown,
        .set_termios    = liteuart_set_termios,
        .type           = liteuart_type,
        .release_port   = liteuart_release_port,
        .request_port   = liteuart_request_port,
        .config_port    = liteuart_config_port,
        .verify_port    = liteuart_verify_port,
};

static int liteuart_probe(struct platform_device *pdev)
{
        struct liteuart_port *uart;
        struct uart_port *port;
        struct xa_limit limit;
        int dev_id, ret;

        /* look for aliases; auto-enumerate for free index if not found */
        dev_id = of_alias_get_id(pdev->dev.of_node, "serial");
        if (dev_id < 0)
                limit = XA_LIMIT(0, CONFIG_SERIAL_LITEUART_MAX_PORTS);
        else
                limit = XA_LIMIT(dev_id, dev_id);

        uart = devm_kzalloc(&pdev->dev, sizeof(struct liteuart_port), GFP_KERNEL);
        if (!uart)
                return -ENOMEM;

        ret = xa_alloc(&liteuart_array, &dev_id, uart, limit, GFP_KERNEL);
        if (ret)
                return ret;

        uart->id = dev_id;
        port = &uart->port;

        /* get membase */
        port->membase = devm_platform_get_and_ioremap_resource(pdev, 0, NULL);
        if (IS_ERR(port->membase))
                return PTR_ERR(port->membase);

        /* values not from device tree */
        port->dev = &pdev->dev;
        port->iotype = UPIO_MEM;
        port->flags = UPF_BOOT_AUTOCONF;
        port->ops = &liteuart_ops;
        port->regshift = 2;
        port->fifosize = 16;
        port->iobase = 1;
        port->type = PORT_UNKNOWN;
        port->line = dev_id;
        spin_lock_init(&port->lock);

        return uart_add_one_port(&liteuart_driver, &uart->port);
}

static int liteuart_remove(struct platform_device *pdev)
{
        struct uart_port *port = platform_get_drvdata(pdev);
        struct liteuart_port *uart = to_liteuart_port(port);

        xa_erase(&liteuart_array, uart->id);

        return 0;
}

static const struct of_device_id liteuart_of_match[] = {
        { .compatible = "litex,liteuart" },
        {}
};
MODULE_DEVICE_TABLE(of, liteuart_of_match);

static struct platform_driver liteuart_platform_driver = {
        .probe = liteuart_probe,
        .remove = liteuart_remove,
        .driver = {
                .name = "liteuart",
                .of_match_table = liteuart_of_match,
        },
};

#ifdef CONFIG_SERIAL_LITEUART_CONSOLE

static void liteuart_console_write(struct console *co, const char *s,
        unsigned int count)
{
        struct liteuart_port *uart;
        struct uart_port *port;
        unsigned long flags;

        uart = (struct liteuart_port *)xa_load(&liteuart_array, co->index);
        port = &uart->port;

        spin_lock_irqsave(&port->lock, flags);
        uart_console_write(port, s, count, liteuart_putchar);
        spin_unlock_irqrestore(&port->lock, flags);
}

static int liteuart_console_setup(struct console *co, char *options)
{
        struct liteuart_port *uart;
        struct uart_port *port;
        int baud = 115200;
        int bits = 8;
        int parity = 'n';
        int flow = 'n';

        uart = (struct liteuart_port *)xa_load(&liteuart_array, co->index);
        if (!uart)
                return -ENODEV;

        port = &uart->port;
        if (!port->membase)
                return -ENODEV;

        if (options)
                uart_parse_options(options, &baud, &parity, &bits, &flow);

        return uart_set_options(port, co, baud, parity, bits, flow);
}

static struct console liteuart_console = {
        .name = "liteuart",
        .write = liteuart_console_write,
        .device = uart_console_device,
        .setup = liteuart_console_setup,
        .flags = CON_PRINTBUFFER,
        .index = -1,
        .data = &liteuart_driver,
};

static int __init liteuart_console_init(void)
{
        register_console(&liteuart_console);

        return 0;
}
console_initcall(liteuart_console_init);
#endif /* CONFIG_SERIAL_LITEUART_CONSOLE */

static int __init liteuart_init(void)
{
        int res;

        res = uart_register_driver(&liteuart_driver);
        if (res)
                return res;

        res = platform_driver_register(&liteuart_platform_driver);
        if (res) {
                uart_unregister_driver(&liteuart_driver);
                return res;
        }

        return 0;
}

static void __exit liteuart_exit(void)
{
        platform_driver_unregister(&liteuart_platform_driver);
        uart_unregister_driver(&liteuart_driver);
}

module_init(liteuart_init);
module_exit(liteuart_exit);

MODULE_AUTHOR("Antmicro <www.antmicro.com>");
MODULE_DESCRIPTION("LiteUART serial driver");
MODULE_LICENSE("GPL v2");
MODULE_ALIAS("platform: liteuart");