how to switch off lcd by using drm ?

[Jzhua]

i‘m not using qt or other 3rd gui framweork, no weston, no x, just direct use drm api，i need switch off lcd after some time is not operated，i google it a while，It looks i need a complete desktop environment to do that，so i want know is any way to do that easily.

now i can simply switch off backlight to look like the lcd is off

[Olivier GALLIEN]

Hi @Jzhua​ ,

I understand playing with backlight is a valid method but maybe not achieving best result in term of power consumption. ( https://wiki.st.com/stm32mpu/wiki/How_to_modify_the_panel_backlight )

I escalate your point to some expert. Keep you posted.

Olivier

[Jzhua]

Okay, I will continue to learn about the content

[Olivier GALLIEN]

Hi @Jzhua​ ,

I found some help from expert :

We have implemented “atomic�? drm/kms drivers so dpms is managed thanks to the CRTC “active�? drm property (prop_active in the uapi, “ACTIVE�? with the libdrm).

In the modetest source code, you can find functions calls setting or resetting the “active�? value (https://github.com/grate-driver/libdrm/blob/master/tests/modetest/modetest.c#L1315

When the CRTC is not anymore in the active state, the panel disable() then unprepare() functions are called (see https://cgit.freedesktop.org/drm/drm-misc/tree/drivers/gpu/drm/panel/panel-orisetech-otm8009a.c#n246).

The “modetest�? command will show the CRTC “ACTIVE�? state current value.

More documentations :

https://elixir.bootlin.com/linux/v5.10.61/source/include/drm/drm_mode_config.h#L659

https://elixir.bootlin.com/linux/v5.10.61/source/drivers/gpu/drm/drm_crtc.c#L212

Hope it help

Olivier

[Jzhua]

i found a easy way to do that

void drm_blank(int blank)
{
	if(lcd_drm && lcd_drm->main_monitor_crtc){
		if(blank){
			// disbale crtc
			drmModeSetCrtc(lcd_drm->fd, lcd_drm->main_monitor_crtc->crtc_id,
					0, // fb_id
					0, 0, // x,y
					NULL, // connectors
					0, // connector_count
					NULL); // mode
		}else{
			struct modeset_buf* buf = &lcd_drm->dev->bufs[lcd_drm->dev->front_buf];
			// enable crtc
			drmModeSetCrtc(lcd_drm->fd, lcd_drm->main_monitor_crtc->crtc_id,
					buf->fb,
					0, 0, // x,y
					&lcd_drm->dev->conn,
					1, // connector_count
					&lcd_drm->dev->mode);
		}
	}
}