sandbox: Add TTY configuration for TKey serial communication

Add os_tty_set_params() function to configure terminal devices for
serial communication with TKey devices:

  - Custom baud rate of 62500 using termios2
  - 8n1 configuration (8 data bits, no parity, 1 stop bit)
  - Raw mode for binary communication
  - Appropriate timeouts for frame-based protocols

This is needed for serial-based TKey communication on sandbox, allowing
U-Boot to communicate with TKey security tokens via a serial port.

Co-developed-by: Claude <noreply@anthropic.com>
Signed-off-by: Simon Glass <sjg@chromium.org>

arch/sandbox/cpu/Makefile

@@ -5,7 +5,7 @@
 # (C) Copyright 2000-2003
 # Wolfgang Denk, DENX Software Engineering, wd@denx.de.
 
-obj-y	:= cache.o cpu.o mem.o state.o os.o
+obj-y	:= cache.o cpu.o mem.o state.o os.o tty.o
 ifdef CONFIG_FUZZ
 obj-y	+= fuzz.o
 else
@@ -17,7 +17,7 @@ obj-$(CONFIG_XPL_BUILD)	+= spl.o
 obj-$(CONFIG_ETH_SANDBOX_RAW)	+= eth-raw-os.o
 
 # Compile these files with system headers
-CFLAGS_USE_SYSHDRS := eth-raw-os.o fuzz.o main.o os.o sdl.o
+CFLAGS_USE_SYSHDRS := eth-raw-os.o fuzz.o main.o os.o sdl.o tty.o
 
 # sdl.c fails to build with -fshort-wchar using musl
 cmd_cc_sdl.o = $(CC) $(filter-out -nostdinc -fshort-wchar, \

arch/sandbox/cpu/tty.c

@@ -0,0 +1,56 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * Copyright (c) 2024 U-Boot TKey Support
+ *
+ * TTY configuration for TKey serial communication
+ */
+
+#define _GNU_SOURCE
+
+#include <errno.h>
+#include <stdio.h>
+#include <unistd.h>
+#include <asm/termbits.h>
+#include <sys/ioctl.h>
+#include <linux/serial.h>
+
+int os_tty_set_params(int fd)
+{
+	struct termios2 tty2;
+
+	/* Get current termios2 attributes */
+	if (ioctl(fd, TCGETS2, &tty2) != 0)
+		return -errno;
+
+	/* Configure for raw mode */
+	tty2.c_iflag &= ~(IGNBRK | BRKINT | PARMRK | ISTRIP | INLCR | IGNCR | ICRNL | IXON);
+	tty2.c_oflag &= ~OPOST;
+	tty2.c_lflag &= ~(ECHO | ECHONL | ICANON | ISIG | IEXTEN);
+	tty2.c_cflag &= ~(CSIZE | PARENB);
+
+	/* 8N1 configuration */
+	tty2.c_cflag |= CS8;                /* 8 data bits */
+	tty2.c_cflag &= ~PARENB;            /* No parity */
+	tty2.c_cflag &= ~CSTOPB;            /* 1 stop bit */
+	tty2.c_cflag |= (CLOCAL | CREAD);   /* Enable receiver, ignore modem lines */
+
+	/* Set custom baud rate using termios2 */
+	tty2.c_cflag &= ~CBAUD;
+	tty2.c_cflag |= BOTHER;             /* Use custom baud rate */
+	tty2.c_ispeed = 62500;              /* Input speed */
+	tty2.c_ospeed = 62500;              /* Output speed */
+
+	/* Blocking with timeout for complete frames */
+	tty2.c_cc[VMIN] = 1;   /* Wait for at least 1 character */
+	tty2.c_cc[VTIME] = 50; /* 5 second timeout */
+
+	/* Apply termios2 settings */
+	if (ioctl(fd, TCSETS2, &tty2) != 0)
+		return -errno;
+
+	/* Flush buffers */
+	if (ioctl(fd, TCFLSH, TCIOFLUSH) != 0)
+		return -errno;
+
+	return 0;
+}

include/os.h

@@ -185,6 +185,18 @@ void os_raise_sigalrm(void);
  */
 void os_tty_raw(int fd, bool allow_sigs);
 
+/**
+ * os_tty_set_params() - configure terminal parameters
+ *
+ * Configure the terminal device for serial communication with specific
+ * baud rate, data bits, parity, and flow control suitable for embedded
+ * device protocols like TKey.
+ *
+ * @fd:		file descriptor of terminal device
+ * Return:	0 on success, -errno on error
+ */
+int os_tty_set_params(int fd);
+
 /**
  * os_fd_restore() - restore the tty to its original mode
  *