On Tuesday 10 August 2021 21:49:28 Pali Rohár wrote:
> Setting custom baudrate for which is not defined Bnnn constant is possible
> via BOTHER flag and then filling speed in c_ospeed and c_ispeed fields.
>
> These two fields are either in struct termios or struct termios2. Former
> belongs to TCGETS/TCSETS ioctls, latter to TCGETS2/TCSETS2 ioctls.
>
> BOTHER flag with these two fields and new struct termios2 is not supported
> by older versions of include header files.
>
> Some architectures (e.g. amd64) provide both struct termios and struct
> termios2, but c_ospeed and c_ispeed are only in struct termios2.
>
> Some other architectures (e.g. alpha) provide both struct termios and struct
> termios2 and both have c_ospeed and c_ispeed fields.
>
> And some other architectures (e.g. powerpc) provide only struct termios
> (no struct termios2) and it has c_ospeed and c_ispeed fields.
>
> So basically to support all architectures it is needed to use
> struct termios2 when TCGETS2/TCSETS2 is supported. Otherwise it is needed
> to use struct termios with TCGETS/TCSETS (case for e.g. powerpc).
>
> Setting input baudrate is done via IBSHIFT macro.
>
> Signed-off-by: Pali Rohár <pali@xxxxxxxxxx>
Hello! Do you have any comments on this patch?
> ---
> Changes in v4:
> * Add SPDX-License-Identifier
> * Correctly process split baudrates (separate output and input) via IBSHIFT
> * Update commit message
>
> Changes in v3:
> * Check support for custom baudrate only based on BOTHER macro
> * Use TCGETS/TCSETS/termios when TCGETS2/TCSETS2/termios2 is not available
>
> Changes in v2:
> * Use \e for backslash
> * Use exit(EXIT_*) instead of return num
> * Sort includes
> * Add comment about possible fallback
> ---
> man2/ioctl_tty.2 | 100 +++++++++++++++++++++++++++++++++++++++++++++++
> 1 file changed, 100 insertions(+)
>
> diff --git a/man2/ioctl_tty.2 b/man2/ioctl_tty.2
> index abfdc1e21fe9..7b2b03ff6757 100644
> --- a/man2/ioctl_tty.2
> +++ b/man2/ioctl_tty.2
> @@ -796,6 +796,106 @@ main(void)
> close(fd);
> }
> .EE
> +.PP
> +Get or set arbitrary baudrate on the serial port.
> +.PP
> +.EX
> +/* SPDX-License-Identifier: GPL-2.0-or-later */
> +
> +#include <asm/termbits.h>
> +#include <fcntl.h>
> +#include <stdio.h>
> +#include <stdlib.h>
> +#include <sys/ioctl.h>
> +#include <sys/types.h>
> +#include <unistd.h>
> +
> +int
> +main(int argc, char *argv[])
> +{
> +#ifndef BOTHER
> + fprintf(stderr, "BOTHER is unsupported\en");
> + /* Program may fallback to TCGETS/TCSETS with Bnnn constants */
> + exit(EXIT_FAILURE);
> +#else
> + /* Declare tio structure, its type depends on supported ioctl */
> +#ifdef TCGETS2
> + struct termios2 tio;
> +#else
> + struct termios tio;
> +#endif
> + int fd, rc;
> +
> + if (argc != 2 && argc != 3 && argc != 4) {
> + fprintf(stderr, "Usage: %s device [output [input] ]\en", argv[0]);
> + exit(EXIT_FAILURE);
> + }
> +
> + fd = open(argv[1], O_RDWR | O_NONBLOCK | O_NOCTTY);
> + if (fd < 0) {
> + perror("open");
> + exit(EXIT_FAILURE);
> + }
> +
> + /* Get the current serial port settings via supported ioctl */
> +#ifdef TCGETS2
> + rc = ioctl(fd, TCGETS2, &tio);
> +#else
> + rc = ioctl(fd, TCGETS, &tio);
> +#endif
> + if (rc) {
> + perror("TCGETS");
> + close(fd);
> + exit(EXIT_FAILURE);
> + }
> +
> + /* Change baud rate when more arguments were provided */
> + if (argc == 3 || argc == 4) {
> + /* Clear the current output baud rate and fill a new value */
> + tio.c_cflag &= ~CBAUD;
> + tio.c_cflag |= BOTHER;
> + tio.c_ospeed = atoi(argv[2]);
> +
> + /* Clear the current input baud rate and fill a new value */
> + tio.c_cflag &= ~(CBAUD << IBSHIFT);
> + tio.c_cflag |= BOTHER << IBSHIFT;
> + /* When 4th argument is not provided reuse output baud rate */
> + tio.c_ispeed = (argc == 4) ? atoi(argv[3]) : atoi(argv[2]);
> +
> + /* Set new serial port settings via supported ioctl */
> +#ifdef TCSETS2
> + rc = ioctl(fd, TCSETS2, &tio);
> +#else
> + rc = ioctl(fd, TCSETS, &tio);
> +#endif
> + if (rc) {
> + perror("TCSETS");
> + close(fd);
> + exit(EXIT_FAILURE);
> + }
> +
> + /* And get new values which were really configured */
> +#ifdef TCGETS2
> + rc = ioctl(fd, TCGETS2, &tio);
> +#else
> + rc = ioctl(fd, TCGETS, &tio);
> +#endif
> + if (rc) {
> + perror("TCGETS");
> + close(fd);
> + exit(EXIT_FAILURE);
> + }
> + }
> +
> + close(fd);
> +
> + printf("output baud rate: %u\en", tio.c_ospeed);
> + printf("input baud rate: %u\en", tio.c_ispeed);
> +
> + exit(EXIT_SUCCESS);
> +#endif
> +}
> +.EE
> .SH SEE ALSO
> .BR ldattach (1),
> .BR ioctl (2),
> --
> 2.20.1
>
