Use your Steam Deck as a USB printer

Gadget Printer.md

Demo video https://streamable.com/02rtwf

Steam Deck can work as a USB gadget.

Assuming dual role device is enabled under BIOS

sudo modprobe g_printer
gcc -o prnt prnt.c
sudo ./prnt -read_data | ps2pdf - out.pdf && flatpak run io.mpv.Mpv ../prnt.mp3 && okular out.pdf

Code modified from https://www.kernel.org/doc/Documentation/usb/gadget_printer.rst

prnt.c

#include <stdio.h>
  #include <stdlib.h>
  #include <fcntl.h>
  #include <linux/poll.h>
  #include <sys/ioctl.h>
  #include <linux/usb/g_printer.h>

  #define PRINTER_FILE			"/dev/g_printer0"
  #define BUF_SIZE			512


  /*
   * 'usage()' - Show program usage.
   */

  static void
  usage(const char *option)		/* I - Option string or NULL */
  {
	if (option) {
		fprintf(stderr,"prn_example: Unknown option \"%s\"!\n",
				option);
	}

	fputs("\n", stderr);
	fputs("Usage: prn_example -[options]\n", stderr);
	fputs("Options:\n", stderr);
	fputs("\n", stderr);
	fputs("-get_status    Get the current printer status.\n", stderr);
	fputs("-selected      Set the selected status to selected.\n", stderr);
	fputs("-not_selected  Set the selected status to NOT selected.\n",
			stderr);
	fputs("-error         Set the error status to error.\n", stderr);
	fputs("-no_error      Set the error status to NO error.\n", stderr);
	fputs("-paper_out     Set the paper status to paper out.\n", stderr);
	fputs("-paper_loaded  Set the paper status to paper loaded.\n",
			stderr);
	fputs("-read_data     Read printer data from driver.\n", stderr);
	fputs("-write_data    Write printer sata to driver.\n", stderr);
	fputs("-NB_read_data  (Non-Blocking) Read printer data from driver.\n",
			stderr);
	fputs("\n\n", stderr);

	exit(1);
  }


  static int
  read_printer_data()
  {
	struct pollfd	fd[1];

	/* Open device file for printer gadget. */
	fd[0].fd = open(PRINTER_FILE, O_RDWR);
	if (fd[0].fd < 0) {
		printf("Error %d opening %s\n", fd[0].fd, PRINTER_FILE);
		close(fd[0].fd);
		return(-1);
	}

	fd[0].events = POLLIN | POLLRDNORM;

	    while (1) {
        static char buf[BUF_SIZE];
        int bytes_read;
        int retval;

        /* Wait for up to 1 second for data. */
        retval = poll(fd, 1, 1000);

        if (retval && (fd[0].revents & POLLRDNORM)) {

            /* Read data from printer gadget driver. */
            bytes_read = read(fd[0].fd, buf, BUF_SIZE);

            if (bytes_read < 0) {
                printf("Error %d reading from %s\n",
                        fd[0].fd, PRINTER_FILE);
                close(fd[0].fd);
                return(-1);
            } else if (bytes_read > 0) {
                /* Write data to standard OUTPUT (stdout). */
                fwrite(buf, 1, bytes_read, stdout);
                fflush(stdout);
            }

        } else if (bytes_read > 0) {
            break;
        }

    }

	/* Close the device file. */
	close(fd[0].fd);

	return 0;
  }


  static int
  write_printer_data()
  {
	struct pollfd	fd[1];

	/* Open device file for printer gadget. */
	fd[0].fd = open (PRINTER_FILE, O_RDWR);
	if (fd[0].fd < 0) {
		printf("Error %d opening %s\n", fd[0].fd, PRINTER_FILE);
		close(fd[0].fd);
		return(-1);
	}

	fd[0].events = POLLOUT | POLLWRNORM;

	while (1) {
		int retval;
		static char buf[BUF_SIZE];
		/* Read data from standard INPUT (stdin). */
		int bytes_read = fread(buf, 1, BUF_SIZE, stdin);

		if (!bytes_read) {
			break;
		}

		while (bytes_read) {

			/* Wait for up to 1 second to sent data. */
			retval = poll(fd, 1, 1000);

			/* Write data to printer gadget driver. */
			if (retval && (fd[0].revents & POLLWRNORM)) {
				retval = write(fd[0].fd, buf, bytes_read);
				if (retval < 0) {
					printf("Error %d writing to %s\n",
							fd[0].fd,
							PRINTER_FILE);
					close(fd[0].fd);
					return(-1);
				} else {
					bytes_read -= retval;
				}

			}

		}

	}

	/* Wait until the data has been sent. */
	fsync(fd[0].fd);

	/* Close the device file. */
	close(fd[0].fd);

	return 0;
  }


  static int
  read_NB_printer_data()
  {
	int		fd;
	static char	buf[BUF_SIZE];
	int		bytes_read;

	/* Open device file for printer gadget. */
	fd = open(PRINTER_FILE, O_RDWR|O_NONBLOCK);
	if (fd < 0) {
		printf("Error %d opening %s\n", fd, PRINTER_FILE);
		close(fd);
		return(-1);
	}

	while (1) {
		/* Read data from printer gadget driver. */
		bytes_read = read(fd, buf, BUF_SIZE);
		if (bytes_read <= 0) {
			break;
		}

		/* Write data to standard OUTPUT (stdout). */
		fwrite(buf, 1, bytes_read, stdout);
		fflush(stdout);
	}

	/* Close the device file. */
	close(fd);

	return 0;
  }


  static int
  get_printer_status()
  {
	int	retval;
	int	fd;

	/* Open device file for printer gadget. */
	fd = open(PRINTER_FILE, O_RDWR);
	if (fd < 0) {
		printf("Error %d opening %s\n", fd, PRINTER_FILE);
		close(fd);
		return(-1);
	}

	/* Make the IOCTL call. */
	retval = ioctl(fd, GADGET_GET_PRINTER_STATUS);
	if (retval < 0) {
		fprintf(stderr, "ERROR: Failed to set printer status\n");
		return(-1);
	}

	/* Close the device file. */
	close(fd);

	return(retval);
  }


  static int
  set_printer_status(unsigned char buf, int clear_printer_status_bit)
  {
	int	retval;
	int	fd;

	retval = get_printer_status();
	if (retval < 0) {
		fprintf(stderr, "ERROR: Failed to get printer status\n");
		return(-1);
	}

	/* Open device file for printer gadget. */
	fd = open(PRINTER_FILE, O_RDWR);

	if (fd < 0) {
		printf("Error %d opening %s\n", fd, PRINTER_FILE);
		close(fd);
		return(-1);
	}

	if (clear_printer_status_bit) {
		retval &= ~buf;
	} else {
		retval |= buf;
	}

	/* Make the IOCTL call. */
	if (ioctl(fd, GADGET_SET_PRINTER_STATUS, (unsigned char)retval)) {
		fprintf(stderr, "ERROR: Failed to set printer status\n");
		return(-1);
	}

	/* Close the device file. */
	close(fd);

	return 0;
  }


  static int
  display_printer_status()
  {
	char	printer_status;

	printer_status = get_printer_status();
	if (printer_status < 0) {
		fprintf(stderr, "ERROR: Failed to get printer status\n");
		return(-1);
	}

	printf("Printer status is:\n");
	if (printer_status & PRINTER_SELECTED) {
		printf("     Printer is Selected\n");
	} else {
		printf("     Printer is NOT Selected\n");
	}
	if (printer_status & PRINTER_PAPER_EMPTY) {
		printf("     Paper is Out\n");
	} else {
		printf("     Paper is Loaded\n");
	}
	if (printer_status & PRINTER_NOT_ERROR) {
		printf("     Printer OK\n");
	} else {
		printf("     Printer ERROR\n");
	}

	return(0);
  }


  int
  main(int  argc, char *argv[])
  {
	int	i;		/* Looping var */
	int	retval = 0;

	/* No Args */
	if (argc == 1) {
		usage(0);
		exit(0);
	}

	for (i = 1; i < argc && !retval; i ++) {

		if (argv[i][0] != '-') {
			continue;
		}

		if (!strcmp(argv[i], "-get_status")) {
			if (display_printer_status()) {
				retval = 1;
			}

		} else if (!strcmp(argv[i], "-paper_loaded")) {
			if (set_printer_status(PRINTER_PAPER_EMPTY, 1)) {
				retval = 1;
			}

		} else if (!strcmp(argv[i], "-paper_out")) {
			if (set_printer_status(PRINTER_PAPER_EMPTY, 0)) {
				retval = 1;
			}

		} else if (!strcmp(argv[i], "-selected")) {
			if (set_printer_status(PRINTER_SELECTED, 0)) {
				retval = 1;
			}

		} else if (!strcmp(argv[i], "-not_selected")) {
			if (set_printer_status(PRINTER_SELECTED, 1)) {
				retval = 1;
			}

		} else if (!strcmp(argv[i], "-error")) {
			if (set_printer_status(PRINTER_NOT_ERROR, 1)) {
				retval = 1;
			}

		} else if (!strcmp(argv[i], "-no_error")) {
			if (set_printer_status(PRINTER_NOT_ERROR, 0)) {
				retval = 1;
			}

		} else if (!strcmp(argv[i], "-read_data")) {
			if (read_printer_data()) {
				retval = 1;
			}

		} else if (!strcmp(argv[i], "-write_data")) {
			if (write_printer_data()) {
				retval = 1;
			}

		} else if (!strcmp(argv[i], "-NB_read_data")) {
			if (read_NB_printer_data()) {
				retval = 1;
			}

		} else {
			usage(argv[i]);
			retval = 1;
		}
	}

	exit(retval);
  }

That was one issue, but ultimately the network also had to be configured differently. We've managed to figure it out, though :) Here's the result:

https://gist.github.com/cheater/00279e5b3dea743e14cf7bcd57f6c7fa

Cool!

https://hackaday.com/2023/01/31/steamdeck-become-printer/

Could you please add a license information (I think it is GPL v2) and convert it into a "normal" repository?

You can convert gists?

I linked to the source of the C (and realistically it was just one line added so it exits after the chunk of data is sent)

I'm not sure of the license of the original as it's not noted in the text file

@parkerlreed , you can use this https://stackoverflow.com/a/37144960/5287257 to convert your gist into a normal repo.
At least there will be better "Issues" tab instead of plain comments.

About a license — I thought everything connected with the Linux kernel is GPL v2, but I can't find proof about the documentation examples.

It looks like the RNDIS gadget isn't going to work for sharing internet from Windows after all - looks like Windows support is dodgy:

https://gist.github.com/dafta/0aadeba3aa8bcbbc8b92a233977571ed?permalink_comment_id=4460779#gistcomment-4460779

Maybe you + dafta can figure out a way to use the ethernet gadget?

@parkerlreed , you can use this https://stackoverflow.com/a/37144960/5287257 to convert your gist into a normal repo. At least there will be better "Issues" tab instead of plain comments.

https://github.com/parkerlreed/gadget-print