iMX8M HDMI

Table of Contents

1. Limitation
2. Rotation
3. Boot Parameters

HDMI

This manual shows how to get HDMI parameters using the CompuLab Yocto Linux:

Discovered

• Video Mode Limitation

imx8 is able to set a video mode described in the edid_cea_modes array:

static struct drm_display_mode edid_cea_modes[] = {
	/* user defined - 1024@768@70Hz */
	{ DRM_MODE("1024x768", DRM_MODE_TYPE_DRIVER, 74250, 1024, 1072,
		   1176, 1328, 0, 768, 771, 775, 798, 0,
		   DRM_MODE_FLAG_PHSYNC | DRM_MODE_FLAG_PVSYNC),
	  .vrefresh = 60, .picture_aspect_ratio = HDMI_PICTURE_ASPECT_16_9, },
	/* user defined - 1366x768@52Hz */
	{ DRM_MODE("1366x768", DRM_MODE_TYPE_DRIVER, 74250, 1366, 1436,
		   1579, 1792, 0, 768, 771, 774, 798, 0,
		   DRM_MODE_FLAG_PHSYNC | DRM_MODE_FLAG_PVSYNC),
	  .vrefresh = 60, .picture_aspect_ratio = HDMI_PICTURE_ASPECT_16_9, },
	/* 3 - 720x480@60Hz */
	{ DRM_MODE("720x480", DRM_MODE_TYPE_DRIVER, 27000, 720, 736,
		   798, 858, 0, 480, 489, 495, 525, 0,
		   DRM_MODE_FLAG_NHSYNC | DRM_MODE_FLAG_NVSYNC),
	  .vrefresh = 60, .picture_aspect_ratio = HDMI_PICTURE_ASPECT_16_9, },
	/* 4 - 1280x720@60Hz */
	{ DRM_MODE("1280x720", DRM_MODE_TYPE_DRIVER, 74250, 1280, 1390,
		   1430, 1650, 0, 720, 725, 730, 750, 0,
		   DRM_MODE_FLAG_PHSYNC | DRM_MODE_FLAG_PVSYNC),
	  .vrefresh = 60, .picture_aspect_ratio = HDMI_PICTURE_ASPECT_16_9, },
	/* 16 - 1920x1080@60Hz */
	{ DRM_MODE("1920x1080", DRM_MODE_TYPE_DRIVER, 148500, 1920, 2008,
		   2052, 2200, 0, 1080, 1084, 1089, 1125, 0,
		   DRM_MODE_FLAG_PHSYNC | DRM_MODE_FLAG_PVSYNC),
	  .vrefresh = 60, .picture_aspect_ratio = HDMI_PICTURE_ASPECT_16_9, },

	/* 97 - 3840x2160@60Hz */
	{ DRM_MODE("3840x2160", DRM_MODE_TYPE_DRIVER, 594000,
		   3840, 4016, 4104, 4400, 0,
		   2160, 2168, 2178, 2250, 0,
		   DRM_MODE_FLAG_PHSYNC | DRM_MODE_FLAG_PVSYNC),
	  .vrefresh = 60, .picture_aspect_ratio = HDMI_PICTURE_ASPECT_16_9, },
	/* 96 - 3840x2160@30Hz */
	{ DRM_MODE("3840x2160", DRM_MODE_TYPE_DRIVER, 297000,
		   3840, 4016, 4104, 4400, 0,
		   2160, 2168, 2178, 2250, 0,
		   DRM_MODE_FLAG_PHSYNC | DRM_MODE_FLAG_PVSYNC),
	  .vrefresh = 30, .picture_aspect_ratio = HDMI_PICTURE_ASPECT_16_9, },
};

• Pixel Clock Limitation

Available Pixel Clocks (KHz): 594000; 297000; 148500; 74250; 27000

Device Tree Modification

In order to use one of the defined video modes:

• edid must be disabled:

&hdmi {
	fsl,no_edid;
	status = "okay";
};

• kernel video boot parameter must be defined this way:

video=HDMI-A-1:1366x768@60

imx8 console rotation

• kernel Config

CONFIG_FRAMEBUFFER_CONSOLE_ROTATION=y 

• kernel video boot parameter must be defined this way:

video=HDMI-A-1:1366x768@60 fbcon=rotate:1

• xorg.conf

Section "Device"
    Identifier  "i.MX Accelerated DRM Device"
    Driver      "fbdev"
    Option      "kmsdev"     "/dev/dri/card0"
    Option "Rotate" "CW"
EndSection

Section "ServerFlags"
    Option "BlankTime"  "0"
    Option "StandbyTime"  "0"
    Option "SuspendTime"  "0"
    Option "OffTime"  "0"
    Option "Xinerama"  "off"
    Option "Clone"  "on"
    Option "SWcursor"  "true"
EndSection

Status

cat /sys/class/drm/card1-HDMI-A-1/status

Reported Modes

cat /sys/class/drm/card1-HDMI-A-1/modes

EDID

hexdump -C /sys/class/drm/card1-HDMI-A-1/edid

Current resolution

fbset

Boot parameters for a custom HDMI resolution

Follow this instruction:

1. Reboot the device & stop in U-Boot.
   
2. Issue:
   

env default -a
setenv mmcargs ${mmcargs} '${video}'
setenv video 'video=HDMI-A-1:1280x800@60'
saveenv
boot

Video Parameter

The format is:

video=:x[M][R][-][@][i][m][eDd]

• : Connector, e.g. DVI-I-1, see /sys/class/drm/ for available connectors
• x : resolution
• M: compute a CVT mode?
• R: reduced blanking?
• -: color depth
• @: refresh rate
• i: interlaced (non-CVT mode)
• m: margins?
• e: output forced to on
• d: output forced to off
• D: digital output forced to on (e.g. DVI-I connector)

Here is an example video mode parameter to force HDMI-A-1 to 720x576 interlaced mode at 50Hz:

video=HDMI-A-1:720x576@50i

Custom Panels

• ADA 1024x60@50

Section "Monitor"
	Identifier "Configured ADA Monitor"
	ModelName "ADA Monitor"
	VendorName "ADA"
	# Monitor Manufactured week 1 of 2007
	# EDID version 1.3
	# Digital Display
	DisplaySize 150 100
	Gamma 1.00
	Option "DPMS" "false"
	Modeline 	"Mode 0" 50.00 1024 1064 1112 1152 600 613 616 645 -hsync -vsync 
EndSection

• Video parameter for the 4.9.51 kernel is:

video=disp.screen0_output_mode=EDID:0 video=HDMI-A-1:1280x720@60

⚠️ This is the only option that makes this this panel work on imx8mq CompuLab environment.

The EDID defined resolution does not work yet.