Unknown monitor: how to have better resolution


I have connected my BBB on a Iiyama AS4637UT ABK LCD monitor via a µHDMI → DVI adapter.

On the Monitor Preferences of Gnome, my monitor is not recognized and the best resolution than I could have is 1024x768@60.
My monitor could display in 1280x1024.

I have edited Xorg.conf to add 1280x1024 but this don’t work.

I have also add dvimode=1280x1024MR-16@60 on the uEnv.txt without success too.

Someone did know how to do ?

Sounds like your DVID adapter is not allowing the EDID information to be passed.


This is correct. By default, the drm_fb_helper_single_fb_probe() function in drivers/gpu/drm/drm_fb_helper.c will default to a 16 BPP 1024x768 display if no “video” parameter is passed to the kernel and no EDID block is reported by the display (or the display is not plugged in at the time the video subsystem in the kernel initializes during bootstrapping). Change your “dvimode” to “video=1280x1024-16@60”. If that doesn’t work, set the “@60” to “@75”. 1280x1024 is not a CEA mode, so you won’t get audio when set to that resolution, but you are using a monitor so that probably isn’t a concern.

Lists of the valid CEA modes (modes that support audio over the HDMI) are listed in the edid_cea_modes[] array in drivers/gpu/drm/drm_edid_modes.h. Lists of other valid modes are in the same file in the drm_dmt_modes[] and edid_est_modes[] arrays.


I agree, I think with the µHDMI to DVI converter the EDID informations are not transmitted, but this also could come from my screen.

With “video=1280x1024-16@60” on uEnv.txt It’s the same but I think it’s normal as the problem come from X11 that can’t read EDID informations from my screen so it use VGA default ones.

So, in the /etc/X11/xorg.conf, I have add the following modline:
Modeline “1280x1024@60” 108 1280 1328 1440 1688 1024 1025 1028 1066 +hsync +vsync
corresponding to the characteristic of my screen.

Then now I could use the 1280x1024 resolution.