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

#include <linux/bits.h>
#include <linux/console.h>
#include <linux/interrupt.h>
#include <linux/litex.h>
#include <linux/module.h>
#include <linux/of.h>
#include <linux/platform_device.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           BIT(0)
#define EV_RX           BIT(1)

struct liteuart_port {
        struct uart_port port;
        struct timer_list timer;
        u8 irq_reg;
};

#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 = KBUILD_MODNAME,
        .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_update_irq_reg(struct uart_port *port, bool set, u8 mask)
{
        struct liteuart_port *uart = to_liteuart_port(port);

        if (set)
                uart->irq_reg |= mask;
        else
                uart->irq_reg &= ~mask;

        if (port->irq)
                litex_write8(port->membase + OFF_EV_ENABLE, uart->irq_reg);
}

static void liteuart_stop_tx(struct uart_port *port)
{
        liteuart_update_irq_reg(port, false, EV_TX);
}

static void liteuart_start_tx(struct uart_port *port)
{
        liteuart_update_irq_reg(port, true, EV_TX);
}

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

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

static void liteuart_rx_chars(struct uart_port *port)
{
        unsigned char __iomem *membase = port->membase;
        u8 ch;

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

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

                /* no overflow bits in status */
                if (!(uart_handle_sysrq_char(port, ch)))
                        uart_insert_char(port, 1, 0, ch, TTY_NORMAL);
        }

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

static void liteuart_tx_chars(struct uart_port *port)
{
        u8 ch;

        uart_port_tx(port, ch,
                !litex_read8(port->membase + OFF_TXFULL),
                litex_write8(port->membase + OFF_RXTX, ch));
}

static irqreturn_t liteuart_interrupt(int irq, void *data)
{
        struct liteuart_port *uart = data;
        struct uart_port *port = &uart->port;
        unsigned long flags;
        u8 isr;

        /*
         * if polling, the context would be "in_serving_softirq", so use
         * irq[save|restore] spin_lock variants to cover all possibilities
         */
        uart_port_lock_irqsave(port, &flags);
        isr = litex_read8(port->membase + OFF_EV_PENDING) & uart->irq_reg;
        if (isr & EV_RX)
                liteuart_rx_chars(port);
        if (isr & EV_TX)
                liteuart_tx_chars(port);
        uart_port_unlock_irqrestore(port, flags);

        return IRQ_RETVAL(isr);
}

static void liteuart_timer(struct timer_list *t)
{
        struct liteuart_port *uart = timer_container_of(uart, t, timer);
        struct uart_port *port = &uart->port;

        liteuart_interrupt(0, port);
        mod_timer(&uart->timer, jiffies + uart_poll_timeout(port));
}

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 int liteuart_startup(struct uart_port *port)
{
        struct liteuart_port *uart = to_liteuart_port(port);
        unsigned long flags;
        int ret;

        if (port->irq) {
                ret = request_irq(port->irq, liteuart_interrupt, 0,
                                  KBUILD_MODNAME, uart);
                if (ret) {
                        dev_warn(port->dev,
                                "line %d irq %d failed: switch to polling\n",
                                port->line, port->irq);
                        port->irq = 0;
                }
        }

        uart_port_lock_irqsave(port, &flags);
        /* only enabling rx irqs during startup */
        liteuart_update_irq_reg(port, true, EV_RX);
        uart_port_unlock_irqrestore(port, flags);

        if (!port->irq) {
                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)
{
        struct liteuart_port *uart = to_liteuart_port(port);
        unsigned long flags;

        uart_port_lock_irqsave(port, &flags);
        liteuart_update_irq_reg(port, false, EV_RX | EV_TX);
        uart_port_unlock_irqrestore(port, flags);

        if (port->irq)
                free_irq(port->irq, port);
        else
                timer_delete_sync(&uart->timer);
}

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

        uart_port_lock_irqsave(port, &flags);

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

        uart_port_unlock_irqrestore(port, flags);
}

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

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,
        .startup        = liteuart_startup,
        .shutdown       = liteuart_shutdown,
        .set_termios    = liteuart_set_termios,
        .type           = liteuart_type,
        .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;

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

        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);

        ret = platform_get_irq_optional(pdev, 0);
        if (ret < 0 && ret != -ENXIO)
                return ret;
        if (ret > 0)
                port->irq = 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);

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

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

        platform_set_drvdata(pdev, port);

        ret = uart_add_one_port(&liteuart_driver, &uart->port);
        if (ret)
                goto err_erase_id;

        return 0;

err_erase_id:
        xa_erase(&liteuart_array, dev_id);

        return ret;
}

static void liteuart_remove(struct platform_device *pdev)
{
        struct uart_port *port = platform_get_drvdata(pdev);
        unsigned int line = port->line;

        uart_remove_one_port(&liteuart_driver, port);
        xa_erase(&liteuart_array, line);
}

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 = KBUILD_MODNAME,
                .of_match_table = liteuart_of_match,
        },
};

#ifdef CONFIG_SERIAL_LITEUART_CONSOLE

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

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

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;

        uart_port_lock_irqsave(port, &flags);
        uart_console_write(port, s, count, liteuart_putchar);
        uart_port_unlock_irqrestore(port, 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 = KBUILD_MODNAME,
        .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);

static void early_liteuart_write(struct console *console, const char *s,
                                    unsigned int count)
{
        struct earlycon_device *device = console->data;
        struct uart_port *port = &device->port;

        uart_console_write(port, s, count, liteuart_putchar);
}

static int __init early_liteuart_setup(struct earlycon_device *device,
                                       const char *options)
{
        if (!device->port.membase)
                return -ENODEV;

        device->con->write = early_liteuart_write;
        return 0;
}

OF_EARLYCON_DECLARE(liteuart, "litex,liteuart", early_liteuart_setup);
#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;
}

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");