// SPDX-License-Identifier: GPL-2.0-or-later
/*
 * Dell AIO Serial Backlight board emulator for testing
 * the Linux dell-uart-backlight driver.
 *
 * Copyright (C) 2024 Hans de Goede <hansg@kernel.org>
 */
#include <errno.h>
#include <fcntl.h>
#include <signal.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/ioctl.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <sys/un.h>
#include <termios.h>
#include <unistd.h>

int serial_fd;
int brightness = 50;

static unsigned char dell_uart_checksum(unsigned char *buf, int len)
{
        unsigned char val = 0;

        while (len-- > 0)
                val += buf[len];

        return val ^ 0xff;
}

/* read() will return -1 on SIGINT / SIGTERM causing the mainloop to cleanly exit */
void signalhdlr(int signum)
{
}

int main(int argc, char *argv[])
{
        struct sigaction sigact = { .sa_handler = signalhdlr };
        unsigned char buf[4], csum, response[32];
        const char *version_str = "PHI23-V321";
        struct termios tty, saved_tty;
        int ret, idx, len = 0;

        if (argc != 2) {
                fprintf(stderr, "Invalid or missing arguments\n");
                fprintf(stderr, "Usage: %s <serial-port>\n", argv[0]);
                return 1;
        }

        serial_fd = open(argv[1], O_RDWR | O_NOCTTY);
        if (serial_fd == -1) {
                fprintf(stderr, "Error opening %s: %s\n", argv[1], strerror(errno));
                return 1;
        }

        ret = tcgetattr(serial_fd, &tty);
        if (ret == -1) {
                fprintf(stderr, "Error getting tcattr: %s\n", strerror(errno));
                goto out_close;
        }
        saved_tty = tty;

        cfsetspeed(&tty, 9600);
        cfmakeraw(&tty);
        tty.c_cflag &= ~CSTOPB;
        tty.c_cflag &= ~CRTSCTS;
        tty.c_cflag |= CLOCAL | CREAD;

        ret = tcsetattr(serial_fd, TCSANOW, &tty);
        if (ret == -1) {
                fprintf(stderr, "Error setting tcattr: %s\n", strerror(errno));
                goto out_restore;
        }

        sigaction(SIGINT, &sigact, 0);
        sigaction(SIGTERM, &sigact, 0);

        idx = 0;
        while (read(serial_fd, &buf[idx], 1) == 1) {
                if (idx == 0) {
                        switch (buf[0]) {
                        /* 3 MSB bits: cmd-len + 01010 SOF marker */
                        case 0x6a: len = 3; break;
                        case 0x8a: len = 4; break;
                        default:
                                fprintf(stderr, "Error unexpected first byte: 0x%02x\n", buf[0]);
                                continue; /* Try to sync up with sender */
                        }
                }

                /* Process msg when len bytes have been received */
                if (idx != (len - 1)) {
                        idx++;
                        continue;
                }

                /* Reset idx for next command */
                idx = 0;

                csum = dell_uart_checksum(buf, len - 1);
                if (buf[len - 1] != csum) {
                        fprintf(stderr, "Error checksum mismatch got 0x%02x expected 0x%02x\n",
                                buf[len - 1], csum);
                        continue;
                }

                switch ((buf[0] << 8) | buf[1]) {
                case 0x6a06: /* cmd = 0x06, get version */
                        len = strlen(version_str);
                        strcpy((char *)&response[2], version_str);
                        printf("Get version, reply: %s\n", version_str);
                        break;
                case 0x8a0b: /* cmd = 0x0b, set brightness */
                        if (buf[2] > 100) {
                                fprintf(stderr, "Error invalid brightness param: %d\n", buf[2]);
                                continue;
                        }

                        len = 0;
                        brightness = buf[2];
                        printf("Set brightness %d\n", brightness);
                        break;
                case 0x6a0c: /* cmd = 0x0c, get brightness */
                        len = 1;
                        response[2] = brightness;
                        printf("Get brightness, reply: %d\n", brightness);
                        break;
                case 0x8a0e: /* cmd = 0x0e, set backlight power */
                        if (buf[2] != 0 && buf[2] != 1) {
                                fprintf(stderr, "Error invalid set power param: %d\n", buf[2]);
                                continue;
                        }

                        len = 0;
                        printf("Set power %d\n", buf[2]);
                        break;
                default:
                        fprintf(stderr, "Error unknown cmd 0x%04x\n",
                                (buf[0] << 8) | buf[1]);
                        continue;
                }

                /* Respond with <total-len> <cmd> <data...> <csum> */
                response[0] = len + 3; /* response length in bytes */
                response[1] = buf[1];  /* ack cmd */
                csum = dell_uart_checksum(response, len + 2);
                response[len + 2] = csum;
                ret = write(serial_fd, response, response[0]);
                if (ret != (response[0]))
                        fprintf(stderr, "Error writing %d bytes: %d\n",
                                response[0], ret);
        }

        ret = 0;
out_restore:
        tcsetattr(serial_fd, TCSANOW, &saved_tty);
out_close:
        close(serial_fd);
        return ret;
}