/*
 * Copyright (c) 2025 Ian Marco Moffett and L5 engineers
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 *
 * 1. Redistributions of source code must retain the above copyright notice,
 *    this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. Neither the name of the project nor the names of its
 *    contributors may be used to endorse or promote products derived from
 *    this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
 * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 * POSSIBILITY OF SUCH DAMAGE.
 */

#include <sys/param.h>
#include <sys/types.h>
#include <machine/uart.h>
#include <machine/pio.h>

static inline uint8_t
uart_transmit_empty(void)
{
    return ISSET(UART_REG_LSR, UART_LSR_THRE);
}

void
uart_write(char byte)
{
    while (!uart_transmit_empty());
    outb(UART_REG_THR, byte);
}

int
uart_init(void)
{
    /* Disable interrupts */
    outb(UART_REG_IER, 0x00);

    /* Set DLAB to set baud rate */
    outb(UART_REG_LCR, UART_LCR_DLAB);

    /* Set speed to 57600 baud */
    outb(UART_REG_DLL, UART_DIVISOR(57600));
    outb(UART_REG_IER, 0x00);

    /* Set word size to 8 bits and clear DLAB */
    outb(UART_REG_LCR, UART_LCR_WLS0 | UART_LCR_WLS1);

    /* Disable FIFOs for now... (TODO: Use them) */
    outb(UART_REG_FCR, 0x00);

    /* Test chip in loopback mode */
    outb(UART_REG_MCR, UART_MCR_LOOP);
    outb(UART_REG_THR, 0xF0);
    if (inb(UART_REG_RBR != 0xF0)) {
        return -1;
    }

    /*
     * Mark the data terminal ready and clear
     * loopback mode.
     */
    outb(UART_REG_MCR, UART_MCR_DTR);
    return 0;
}