--- /dev/null
+Emulator for DELL0501 UART attached backlight controller
+--------------------------------------------------------
+
+Dell All In One (AIO) models released after 2017 use a backlight controller
+board connected to an UART.
+
+In DSDT this uart port will be defined as:
+
+ Name (_HID, "DELL0501")
+ Name (_CID, EisaId ("PNP0501")
+
+With the DELL0501 indicating that we are dealing with an UART with
+the backlight controller board attached.
+
+This small emulator allows testing
+the drivers/platform/x86/dell/dell-uart-backlight.c driver without access
+to an actual Dell All In One.
+
+This requires:
+1. A (desktop) PC with a 16550 UART on the motherboard and a standard DB9
+ connector connected to this UART.
+2. A DB9 NULL modem cable.
+3. A second DB9 serial port, this can e.g. be a USB to serial converter
+ with a DB9 connector plugged into the same desktop PC.
+4. A DSDT overlay for the desktop PC replacing the _HID of the 16550 UART
+ ACPI Device() with "DELL0501" and adding a _CID of "PNP0501", see
+ DSDT.patch for an example of the necessary DSDT changes.
+
+With everything setup and the NULL modem cable connected between
+the 2 serial ports run:
+
+./dell-uart-backlight-emulator <path-to-/dev/tty*S#-for-second-port>
+
+For example when using an USB to serial converter for the second port:
+
+./dell-uart-backlight-emulator /dev/ttyUSB0
+
+And then (re)load the dell-uart-backlight driver:
+
+sudo rmmod dell-uart-backlight; sudo modprobe dell-uart-backlight dyndbg
+
+After this check "dmesg" to see if the driver correctly received
+the firmware version string from the emulator. If this works there
+should be a /sys/class/backlight/dell_uart_backlight/ directory now
+and writes to the brightness or bl_power files should be reflected
+by matching output from the emulator.
--- /dev/null
+// 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;
+}
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