Hack to control the keyboard backlight level on a Thinkpad Lenovo X1 Carbon Touch

tmp.c

/* gcc -o tmp `pkg-config --libs --cflags glib-2.0` tmp.c
 *
 * # modprobe ec_sys
 *
 * # watch -n 0.1 hexdump -C /sys/kernel/debug/ec/ec0/io
 *
 * 00000000  a7 05 a0 e2 00 86 05 00  00 00 47 00 00 03 00 10  |..........G.....|
 * 00000000  a7 05 a0 e2 00 86 05 00  00 00 47 00 00 43 00 10  |..........G..C..|
 * 00000000  a7 05 a0 e2 00 86 05 00  00 00 47 00 00 83 00 10  |..........G.....|
 *
 * # ./tmp 0
 * # ./tmp 1
 * # ./tmp 2
 *
 */

#include <glib.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <errno.h>

char levels[] = {
	0x03,
	0x43,
	0x83
};

static void
usage (char **argv)
{
	g_print ("%s [level]\n", argv[0]);
	g_print ("Where level is between 1 and 3\n");
}

int main (int argc, char **argv)
{
	int fd;
	int level;

	if (argc < 2) {
		usage (argv);
		return 1;
	}
	level = atoi(argv[1]);
	if (level < 0 || level > 3) {
		usage (argv);
		return 1;
	}

	fd = open ("/sys/kernel/debug/ec/ec0/io", O_RDWR);
	if (fd < 0) {
		g_print ("open: %s\n", g_strerror (errno));
		return 1;
	}
	if (lseek (fd, 0xd, SEEK_CUR) < 0) {
		g_print ("seek: %s\n", g_strerror (errno));
		return 1;
	}
	if (write (fd, &levels[level], 1) < 0) {
		g_print ("write: %s\n", g_strerror (errno));
		return 1;
	}

	return 0;
}

Thank you for this great gist, as it solved our needed issue. I posted an answer based on this gist:

http://askubuntu.com/questions/383501/enable-the-keyboard-backlights-on-supported-lenovo-e-g-carbon-x1-with-command/

Any chance this will work for the 2014 none touch version?

Thanks! Confirmed this works on a Fedora 20 system, compiled with:

$ gcc -I/usr/include/glib-2.0 -I/usr/lib64/glib-2.0/include thinklight.c -o ThinkLight -lglib-2.0

Dude, nice one. 1 coffee @changetip

is this code gonna work on Toshiba U945, or do I need change this code for getting my keyboard backling works?

I've the 3rd edition of the x1 carbon, running ubuntu on it with kernel 3.19.0-25-generic.
Seems to be that the path on this machine is different. There is no "/sys/kernel/debug/ec/ec0/io" on my system.

root@X1:~# ls /sys/kernel/debug/
acpi           fault_around_bytes  kvm-guest         regulator
bdi            frontswap           mce               sched_features
bluetooth      gpio                mei0              sleep_time
cleancache     hid                 pinctrl           suspend_stats
clk            ieee80211           pkg_temp_thermal  tracing
dma_buf        intel_powerclamp    pstate_snb        usb
dri            iosf_sb             pwm               virtio-ports
dynamic_debug  iwlwifi             ras               wakeup_sources
extfrag  

Any idea?

Thanks in advance!

I am experiencing the same issue as @maltinho, with the same laptop. By the way, even if I expect no difference, my thinkpad is not a touch one.

Hopping this will be solved, thanks in advance

Works on ThinkPad T430s with Ubuntu 14.04, thanks! It's really helpful since my Fn key stopped working.

Here's a version that doesn't need libglib:

/* gcc -Wall -Werror -o backlight backlight.c
 *
 * # modprobe ec_sys
 *
 * # watch -n 0.1 hexdump -C /sys/kernel/debug/ec/ec0/io
 *
 * 00000000  a7 05 a0 e2 00 86 05 00  00 00 47 00 00 03 00 10  |..........G.....|
 * 00000000  a7 05 a0 e2 00 86 05 00  00 00 47 00 00 43 00 10  |..........G..C..|
 * 00000000  a7 05 a0 e2 00 86 05 00  00 00 47 00 00 83 00 10  |..........G.....|
 *
 * # ./backlight 0
 * # ./backlight 1
 * # ./backlight 2
 *
 */

#include <sys/stat.h>
#include <sys/types.h>
#include <errno.h>
#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>

static char levels[] = {
    0x03,
    0x43,
    0x83
};

static void
usage(char **argv)
{
    printf("%s [level]\n", argv[0]);
    printf("Where level is between 1 and 3\n");
}

int
main(int argc, char **argv)
{
    int fd;
    int level;

    if (argc < 2) {
        usage(argv);
        return 1;
    }

    level = atoi(argv[1]);

    if (level < 0 || level > 3) {
        usage(argv);
        return 1;
    }

    fd = open("/sys/kernel/debug/ec/ec0/io", O_RDWR);

    if (fd < 0) {
        printf("open: %s\n", strerror(errno));
        return 1;
    }

    if (lseek(fd, 0xd, SEEK_CUR) < 0) {
        printf("seek: %s\n", strerror(errno));
        return 1;
    }

    if (write(fd, &levels[level], 1) < 0) {
        printf("write: %s\n", strerror(errno));
        return 1;
    }

    return 0;
}

@maltinho, bruno066, just sudo modprobe ec_sys to get that (if your kernel is configured to ship it as a module)

Here is a bash script version which does not require compilation. Works on my X260.

https://gist.github.com/vzaliva/0adba7bc40e2f31a0b5f802af2a63267

Thanks for figuring out registers!

On Fedora at least, compiled versions need chown root:root <filename>; chmod +s <filename> to gain root permissions.

The ec_sys kernel module is not loaded automatically on my system (X230 Tablet) so needs # echo ec_sys > /etc/modules_load.d to load, and #echo options ec_sys write-support=1 > /etc/modprobe.d/ec_sys.conf to be able to write to the relevant device persistently after reboot.

Once that's done, works like a charm!

Can someone tell me how to set this up on X1 Ubuntu 20 so that backlight is persistent? Not sure what steps to take so if someone can write step by step guide.