X11 on Debian 9 image

The recent RPB image is reported to have working framebuffer with kernel 4.13, while with the standard 4.15
i got only this error message

adv7511: probe of 1-0039 failed with error -22

Do i need a 4.13 “downgrade” to have working X11 on Debian 9 ?

I have booted the RPB 4.14 kernel with debian rootfs

root@linaro-developer:~# uname -a
Linux linaro-developer 4.14.0-rc7-linaro-hikey960 #1 SMP PREEMPT Thu Jan 11 00:27:15 UTC 2018 aarch64 GNU/Linux

with 4.14 modules copied to debian rootfs

root@linaro-developer:~# ls -als /lib/modules/
total 16
4 drwxr-xr-x  4 root root 4096 Nov  3 17:18 .
4 drwxr-xr-x 16 root root 4096 Feb 12  2018 ..
4 drwxr-xr-x  3 root root 4096 Nov  3 17:27 4.14.0-rc7-linaro-hikey960
4 drwxr-xr-x  3 root root 4096 Feb 12  2018 4.15-hikey

Debian GNU/Linux 9 linaro-developer ttyAMA6

linaro-developer login: root (automatic login)

Last login: Thu Nov  3 17:16:45 UTC 2016 on ttyAMA6
Linux linaro-developer 4.14.0-rc7-linaro-hikey960 #1 SMP PREEMPT Thu Jan 11 00:27:15 UTC 2018 aarch64

There is something broken in my UEFI/DTB interaction. The board runs very slow because only CPU0 is active

root@linaro-developer:~# cat /proc/cpuinfo 
processor       : 0
BogoMIPS        : 3.84
Features        : fp asimd evtstrm aes pmull sha1 sha2 crc32 cpuid
CPU implementer : 0x41
CPU architecture: 8
CPU variant     : 0x0
CPU part        : 0xd03
CPU revision    : 4

FYI, i have full working KDE + USB UMTS modem + USB GPS + USB ethernet (ASIX) using self-compiled 4.14.0-rc7-linaro-hikey960+
kernel (without any local patches, using modified defconfig)
X11 is a bit slow without 2D hardware acceleration, any ideas how to change that are welcome.

Do your builds have the recently released MALI driver for Hikey960 integrated (like with HDMI support, I don’t really track the RPB status very closely)? A common route to accelerated 2D on modern systems tends to be OpenGL+glamor.

No, i have used the stock RPB kernel.