Keyboard Backlight Control on Lenovo Ideapad & Xiaoxin Models

Ever found the keyboard backlight annoying? It keeps turnning on when booting Windows, and there is no configuration to disable it permanently in any Lenovo Utilities.

Just did some reverse engineering to find how to control keyboard backlight programmatically. The principal is simple, use \\.\EnergyDrv device exposed by Lenovo ACPI energy management driver. It is capable of controlling all keyboard backlight levels. Also other capabilities available . See code:

#include <windows.h>
#include <stdio.h>
#include <stdlib.h>
#include <stdint.h>


#define IOCTL_BACKLIGHT         0x83102144

#define BACKLIGHT_CAPABILITY    0x01
#define BACKLIGHT_STATUS        0x32
#define BACKLIGHT_OFF           0x00033
#define BACKLIGHT_LEVEL1        0x10033
#define BACKLIGHT_LEVEL2        0x20033
#define BACKLIGHT_AUTO          0x30033


char *get_base_name(char *path)
{
    if (!path) {
        return NULL;
    }
    char *an = NULL;
    char *p = path;
    while (*p++) {
        if (*p == '\\' || *p == '/') {
            an = p;
        }
    }
    return (an == NULL) ? path : (an + 1);
}

uint32_t device_io_control(HANDLE drv_handle, uint32_t func)
{
    char outbuff[4] = { 0 };
    DWORD ret_len = 0;
    if (DeviceIoControl(drv_handle, IOCTL_BACKLIGHT, &func, sizeof(func), outbuff, sizeof(outbuff), &ret_len, NULL)) {
        outbuff[ret_len] = '\0';
        return (outbuff[3] << 24) | (outbuff[2] << 16) | (outbuff[1] << 8) | outbuff[0];
    } else {
        fprintf(stderr, "Error: DeviceIoControl failed, func=%d\n", func);
        return (uint32_t) -1;
    }
}

uint32_t get_backlight_capability(HANDLE drv_handle)
{
    return device_io_control(drv_handle, BACKLIGHT_CAPABILITY);
}

uint32_t get_backlight_status(HANDLE drv_handle)
{
    return device_io_control(drv_handle, BACKLIGHT_STATUS);
}

uint32_t set_backlight_level(HANDLE drv_handle, int level)
{
    uint32_t func = BACKLIGHT_AUTO;
    switch (level) {
        case 0:
            func = BACKLIGHT_OFF;
            break;
        case 1:
            func = BACKLIGHT_LEVEL1;
            break;
        case 2:
            func = BACKLIGHT_LEVEL2;
            break;
    }
    return device_io_control(drv_handle, func);
}

int main(int argc, char *argv[])
{
    if (argc != 2) {
        fprintf(stderr, "Usage: %s [0|1|2|3]\n", get_base_name(argv[0]));
        return -1;
    }
    int level = (int) strtol(argv[1], NULL, 0);
    if (level < 0 || level > 3) {
        fprintf(stderr, "Usage: %s [0|1|2|3]\n", get_base_name(argv[0]));
        return -1;
    }
    /* open */
    HANDLE drv_handle = CreateFileA("\\\\.\\EnergyDrv", GENERIC_READ, 0, NULL, OPEN_EXISTING, FILE_ATTRIBUTE_NORMAL, NULL);
    if (drv_handle == INVALID_HANDLE_VALUE) {
        fprintf(stderr, "Error: Failed to find device, make sure Lenovo energy management driver is installed!\n");
        return -1;
    }
    /* run */
    do {
        /* cap */
        uint32_t cap = get_backlight_capability(drv_handle);
        if (cap == (uint32_t) -1) {
            break;
        }
        if ((cap & 1) != 1) {
            fprintf(stderr, "Error: Failed to get capability!\n");
            break;
        }
        if ((cap >> 1) != 3) {
            fprintf(stderr, "Error: Auto-level not supported!\n");
            break;
        }
        /* status */
        uint32_t status = get_backlight_status(drv_handle);
        if (status == (uint32_t) -1) {
            break;
        }
        if ((status & 1) != 1) {
            fprintf(stderr, "Error: Failed to get current status!\n");
            break;
        }
        status = status >> 1;
        if ((status & 0x8000) != 0x8000) {
            fprintf(stderr, "Error: Cannot set backlight when keyboard is disabled!\n");
            break;
        }
        int curr_level = -1;
        switch (status & 0x7fff) {
            case 0:
                curr_level = 0;
                break;
            case 1:
                curr_level = 1;
                break;
            case 2:
                curr_level = 2;
                break;
            case 3:
                curr_level = 3;
                break;
        }
        printf("Current level: %d\n", curr_level);
        set_backlight_level(drv_handle, level);
        printf("Finished setting level: %d\n", level);
    } while (FALSE);
    /* close */
    CloseHandle(drv_handle);
    return 0;
}

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#include <windows.h>

#include <stdio.h>

#include <stdlib.h>

#include <stdint.h>

#define IOCTL_BACKLIGHT 0x83102144

#define BACKLIGHT_CAPABILITY 0x01

#define BACKLIGHT_STATUS 0x32

#define BACKLIGHT_OFF 0x00033

#define BACKLIGHT_LEVEL1 0x10033

#define BACKLIGHT_LEVEL2 0x20033

#define BACKLIGHT_AUTO 0x30033

char *get_base_name(char *path)

{

if (!path) {

return NULL;

}

char *an = NULL;

char *p = path;

while (*p++) {

if (*p == '\\' || *p == '/') {

an = p;

}

return (an == NULL) ? path : (an + 1);

}

uint32_t device_io_control(HANDLE drv_handle, uint32_t func)

{

char outbuff[4] = { 0 };

DWORD ret_len = 0;

if (DeviceIoControl(drv_handle, IOCTL_BACKLIGHT, &func, sizeof(func), outbuff, sizeof(outbuff), &ret_len, NULL)) {

outbuff[ret_len] = '\0';

return (outbuff[3] << 24) | (outbuff[2] << 16) | (outbuff[1] << 8) | outbuff[0];

} else {

fprintf(stderr, "Error: DeviceIoControl failed, func=%d\n", func);

return (uint32_t) -1;

}

uint32_t get_backlight_capability(HANDLE drv_handle)

{

return device_io_control(drv_handle, BACKLIGHT_CAPABILITY);

}

uint32_t get_backlight_status(HANDLE drv_handle)

{

return device_io_control(drv_handle, BACKLIGHT_STATUS);

}

uint32_t set_backlight_level(HANDLE drv_handle, int level)

{

uint32_t func = BACKLIGHT_AUTO;

switch (level) {

case 0:

func = BACKLIGHT_OFF;

break;

case 1:

func = BACKLIGHT_LEVEL1;

break;

case 2:

func = BACKLIGHT_LEVEL2;

break;

}

return device_io_control(drv_handle, func);

}

int main(int argc, char *argv[])

{

if (argc != 2) {

fprintf(stderr, "Usage: %s [0|1|2|3]\n", get_base_name(argv[0]));

return -1;

}

int level = (int) strtol(argv[1], NULL, 0);

if (level < 0 || level > 3) {

fprintf(stderr, "Usage: %s [0|1|2|3]\n", get_base_name(argv[0]));

return -1;

}

/* open */

HANDLE drv_handle = CreateFileA("\\\\.\\EnergyDrv", GENERIC_READ, 0, NULL, OPEN_EXISTING, FILE_ATTRIBUTE_NORMAL, NULL);

if (drv_handle == INVALID_HANDLE_VALUE) {

fprintf(stderr, "Error: Failed to find device, make sure Lenovo energy management driver is installed!\n");

return -1;

}

/* run */

do {

/* cap */

uint32_t cap = get_backlight_capability(drv_handle);

if (cap == (uint32_t) -1) {

break;

}

if ((cap & 1) != 1) {

fprintf(stderr, "Error: Failed to get capability!\n");

break;

}

if ((cap >> 1) != 3) {

fprintf(stderr, "Error: Auto-level not supported!\n");

break;

}

/* status */

uint32_t status = get_backlight_status(drv_handle);

if (status == (uint32_t) -1) {

break;

}

if ((status & 1) != 1) {

fprintf(stderr, "Error: Failed to get current status!\n");

break;

}

status = status >> 1;

if ((status & 0x8000) != 0x8000) {

fprintf(stderr, "Error: Cannot set backlight when keyboard is disabled!\n");

break;

}

int curr_level = -1;

switch (status & 0x7fff) {

case 0:

curr_level = 0;

break;

case 1:

curr_level = 1;

break;

case 2:

curr_level = 2;

break;

case 3:

curr_level = 3;

break;

}

printf("Current level: %d\n", curr_level);

set_backlight_level(drv_handle, level);

printf("Finished setting level: %d\n", level);

} while (FALSE);

/* close */

CloseHandle(drv_handle);

return 0;

}

Should built and run on any C99 compilers. Run with <app.exe> [0|1|2|3]. You can add it to task scheduler to disable keyboard backlight on startup.

Also checked other approaches. The usb/hid way does not work on an ideapad. The Keyboard_Core.dll hack also does not work, I cannot find the file in drivers.

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