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tools arch x86: Add dell-uart-backlight-emulator
Dell All In One (AIO) models released after 2017 use a backlight controller board connected to an UART. Add a small emulator to allow development and testing of the drivers/platform/x86/dell/dell-uart-backlight.c driver for this board, without requiring access to an actual Dell All In One. Signed-off-by: Hans de Goede <[email protected]> Link: https://lore.kernel.org/r/[email protected]
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‎tools/arch/x86/dell-uart-backlight-emulator/.gitignore

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dell-uart-backlight-emulator

‎tools/arch/x86/dell-uart-backlight-emulator/Makefile

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# SPDX-License-Identifier: GPL-2.0
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# Makefile for Intel Software Defined Silicon provisioning tool
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dell-uart-backlight-emulator: dell-uart-backlight-emulator.c
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BINDIR ?= /usr/bin
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override CFLAGS += -O2 -Wall
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%: %.c
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$(CC) $(CFLAGS) -o $@ $< $(LDFLAGS)
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.PHONY : clean
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clean :
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@rm -f dell-uart-backlight-emulator
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install : dell-uart-backlight-emulator
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install -d $(DESTDIR)$(BINDIR)
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install -m 755 -p dell-uart-backlight-emulator $(DESTDIR)$(BINDIR)/dell-uart-backlight-emulator

‎tools/arch/x86/dell-uart-backlight-emulator/README

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

‎tools/arch/x86/dell-uart-backlight-emulator/dell-uart-backlight-emulator.c

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// SPDX-License-Identifier: GPL-2.0-or-later
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/*
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* Dell AIO Serial Backlight board emulator for testing
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* the Linux dell-uart-backlight driver.
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*
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* Copyright (C) 2024 Hans de Goede <[email protected]>
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*/
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#include <errno.h>
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#include <fcntl.h>
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#include <signal.h>
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#include <stdio.h>
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#include <stdlib.h>
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#include <string.h>
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#include <sys/ioctl.h>
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#include <sys/stat.h>
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#include <sys/types.h>
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#include <sys/un.h>
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#include <termios.h>
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#include <unistd.h>
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int serial_fd;
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int brightness = 50;
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static unsigned char dell_uart_checksum(unsigned char *buf, int len)
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{
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unsigned char val = 0;
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while (len-- > 0)
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val += buf[len];
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return val ^ 0xff;
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}
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/* read() will return -1 on SIGINT / SIGTERM causing the mainloop to cleanly exit */
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void signalhdlr(int signum)
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{
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}
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int main(int argc, char *argv[])
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{
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struct sigaction sigact = { .sa_handler = signalhdlr };
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unsigned char buf[4], csum, response[32];
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const char *version_str = "PHI23-V321";
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struct termios tty, saved_tty;
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int ret, idx, len = 0;
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if (argc != 2) {
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fprintf(stderr, "Invalid or missing arguments\n");
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fprintf(stderr, "Usage: %s <serial-port>\n", argv[0]);
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return 1;
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}
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serial_fd = open(argv[1], O_RDWR | O_NOCTTY);
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if (serial_fd == -1) {
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fprintf(stderr, "Error opening %s: %s\n", argv[1], strerror(errno));
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return 1;
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}
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ret = tcgetattr(serial_fd, &tty);
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if (ret == -1) {
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fprintf(stderr, "Error getting tcattr: %s\n", strerror(errno));
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goto out_close;
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}
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saved_tty = tty;
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cfsetspeed(&tty, 9600);
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cfmakeraw(&tty);
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tty.c_cflag &= ~CSTOPB;
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tty.c_cflag &= ~CRTSCTS;
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tty.c_cflag |= CLOCAL | CREAD;
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ret = tcsetattr(serial_fd, TCSANOW, &tty);
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if (ret == -1) {
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fprintf(stderr, "Error setting tcattr: %s\n", strerror(errno));
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goto out_restore;
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}
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sigaction(SIGINT, &sigact, 0);
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sigaction(SIGTERM, &sigact, 0);
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idx = 0;
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while (read(serial_fd, &buf[idx], 1) == 1) {
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if (idx == 0) {
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switch (buf[0]) {
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/* 3 MSB bits: cmd-len + 01010 SOF marker */
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case 0x6a: len = 3; break;
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case 0x8a: len = 4; break;
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default:
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fprintf(stderr, "Error unexpected first byte: 0x%02x\n", buf[0]);
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continue; /* Try to sync up with sender */
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}
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}
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/* Process msg when len bytes have been received */
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if (idx != (len - 1)) {
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idx++;
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continue;
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}
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/* Reset idx for next command */
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idx = 0;
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csum = dell_uart_checksum(buf, len - 1);
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if (buf[len - 1] != csum) {
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fprintf(stderr, "Error checksum mismatch got 0x%02x expected 0x%02x\n",
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buf[len - 1], csum);
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continue;
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}
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switch ((buf[0] << 8) | buf[1]) {
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case 0x6a06: /* cmd = 0x06, get version */
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len = strlen(version_str);
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strcpy((char *)&response[2], version_str);
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printf("Get version, reply: %s\n", version_str);
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break;
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case 0x8a0b: /* cmd = 0x0b, set brightness */
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if (buf[2] > 100) {
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fprintf(stderr, "Error invalid brightness param: %d\n", buf[2]);
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continue;
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}
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len = 0;
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brightness = buf[2];
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printf("Set brightness %d\n", brightness);
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break;
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case 0x6a0c: /* cmd = 0x0c, get brightness */
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len = 1;
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response[2] = brightness;
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printf("Get brightness, reply: %d\n", brightness);
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break;
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case 0x8a0e: /* cmd = 0x0e, set backlight power */
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if (buf[2] != 0 && buf[2] != 1) {
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fprintf(stderr, "Error invalid set power param: %d\n", buf[2]);
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continue;
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}
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len = 0;
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printf("Set power %d\n", buf[2]);
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break;
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default:
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fprintf(stderr, "Error unknown cmd 0x%04x\n",
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(buf[0] << 8) | buf[1]);
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continue;
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}
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/* Respond with <total-len> <cmd> <data...> <csum> */
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response[0] = len + 3; /* response length in bytes */
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response[1] = buf[1]; /* ack cmd */
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csum = dell_uart_checksum(response, len + 2);
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response[len + 2] = csum;
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ret = write(serial_fd, response, response[0]);
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if (ret != (response[0]))
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fprintf(stderr, "Error writing %d bytes: %d\n",
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response[0], ret);
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}
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ret = 0;
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out_restore:
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tcsetattr(serial_fd, TCSANOW, &saved_tty);
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out_close:
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close(serial_fd);
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return ret;
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}

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