On my HP Pavilion dv7 with hybrid graphics (AMD HD 4200 - AMD 5400) X can't be
started anymore. When trying to start X with "startx" Xorg freezes to an
un-killable process before switching to a frame buffer. From another console I'm
able to kill the xinit process which brings the first console back to the shell
prompt. I can find nothing relevant in the logs.

The last few lines in Xorg.0.log are:

...
[    61.007] (==) ModulePath set to "/usr/lib/xorg/modules"
[    61.007] (II) The server relies on udev to provide the list of input devices.
	If no devices become available, reconfigure udev or disable AutoAddDevices.
[    61.007] (II) Loader magic: 0x5571980cbdc0
[    61.008] (II) Module ABI versions:
[    61.008] 	X.Org ANSI C Emulation: 0.4
[    61.008] 	X.Org Video Driver: 20.0
[    61.008] 	X.Org XInput driver : 22.1
[    61.008] 	X.Org Server Extension : 9.0
[    61.009] (++) using VT number 1

[    61.009] (EE) systemd-logind: failed to get session: The name
org.freedesktop.login1 was not provided by any .service files
[    61.010] (II) xfree86: Adding drm device (/dev/dri/card0)
[    61.011] (II) xfree86: Adding drm device (/dev/dri/card1)

which are the same as with 4.4.3. There the log continues with

 [    65.782] (--) PCI:*(0:1:5:0) 1002:9712:103c:1443 rev 0, Mem @
0xd0000000/268435456, 0xf0400000/65536, 0xf0300000/1048576, I/O @ 0x00004000/256
[    65.782] (--) PCI: (0:2:0:0) 1002:68e0:103c:1443 rev 0, Mem @
0xe0000000/268435456, 0xf0200000/131072, I/O @ 0x00003000/256, BIOS @
0x????????/131072
[    65.782] (II) LoadModule: "glx"
[    65.784] (II) Loading /usr/lib/xorg/modules/extensions/libglx.so
[    65.801] (II) Module glx: vendor="X.Org Foundation"
...

I attach the config file.

Regards,
jvp.