Even I am also facing same issue while trying to set the mode on the android device. Here I am attaching the error message. Can anybody help in resolving it?
134|console:/data # ./modeset
using card '/dev/dri/card0'
mode for connector 29 is 1080x1920
mode for connector 47 is 4096x2160
mode for connector 57 is 1920x1080
cannot set CRTC for connector 57 (13): Permission denied
cannot set CRTC for connector 47 (13): Permission denied
cannot set CRTC for connector 29 (13): Permission denied