startx output:
Xorg: drmmode_display.c:807: drmmode_crtc_init: Assertion `ret == 0' failed.
xinit: giving up
xinit: unable to connect to X server: Connection refused
xinit: server error

grep EE /var/log/Xorg.0.log
[    32.548] Current Operating System: Linux pc-sasha 5.3.0-rc3-01537-g6a3068065fa4 #4 SMP Sun Sep 15 17:41:39 EEST 2019 x86_64
        (WW) warning, (EE) error, (NI) not implemented, (??) unknown.
[    32.828] (EE) Failed to load module "nv" (module does not exist, 0)
[    32.861] (EE) Failed to load module "fbdev" (module does not exist, 0)
[    32.861] (EE) Failed to load module "vesa" (module does not exist, 0)
[    32.863] (EE) [drm] Failed to open DRM device for (null): -22
[    32.908] (EE)
[    32.908] (EE) Backtrace:
[    32.908] (EE) 0: /usr/lib/Xorg (xorg_backtrace+0x4d) [0x55b0ae7cc69d]
[    32.908] (EE) 1: /usr/lib/Xorg (0x55b0ae71a000+0xa8be8) [0x55b0ae7c2be8]
[    32.908] (EE) 2: /usr/lib/libc.so.6 (0x7f7b8c8f2000+0x3a7e0) [0x7f7b8c92c7e0]
[    32.908] (EE) 3: /usr/lib/libc.so.6 (gsignal+0x145) [0x7f7b8c92c755]
[    32.908] (EE) 4: /usr/lib/libc.so.6 (abort+0x125) [0x7f7b8c917851]
[    32.908] (EE) 5: /usr/lib/libc.so.6 (0x7f7b8c8f2000+0x25727) [0x7f7b8c917727]
[    32.908] (EE) 6: /usr/lib/libc.so.6 (0x7f7b8c8f2000+0x33026) [0x7f7b8c925026]
[    32.908] (EE) 7: /usr/lib/xorg/modules/drivers/nouveau_drv.so (0x7f7b8b1c9000+0x2a120) [0x7f7b8b1f3120]
[    32.908] (EE) 8: /usr/lib/xorg/modules/drivers/nouveau_drv.so (0x7f7b8b1c9000+0x12f6e) [0x7f7b8b1dbf6e]
[    32.909] (EE) 9: /usr/lib/Xorg (InitOutput+0x13f2) [0x55b0ae7af412]
[    32.909] (EE) 10: /usr/lib/Xorg (0x55b0ae71a000+0x37503) [0x55b0ae751503]
[    32.909] (EE) 11: /usr/lib/libc.so.6 (__libc_start_main+0xf3) [0x7f7b8c918ee3]
[    32.909] (EE) 12: /usr/lib/Xorg (_start+0x2e) [0x55b0ae7523be]
[    32.909] (EE)
[    32.909] (EE)
[    32.909] (EE) Caught signal 6 (Aborted). Server aborting
[    32.909] (EE)
[    32.909] (EE)
[    32.909] (EE) Please also check the log file at "/var/log/Xorg.0.log" for additional information.
[    32.909] (EE)
[    32.912] (EE) Server terminated with error (1). Closing log file.