LL4.8 takes a lot to boot

[SpAiK]

Hi, I recently installed LL 4.8 on an old HP Compaq 6710b laptop. It installed perfectly fine and I'm currently writing this post from there, so it works fine and fast once logged in. But every time I boot (no dual boot, LL only) it takes a lot of time to reach to desktop. Similarly when I shut down, it takes some time to do it, more than it should.
So I've taken a look to dmesg and have found that there is some problem than repeats over boot time (and also at shutdown) and slows things down a lot:

q-6710b-GB889ET-ABE kernel: [  13.280068] [drm:drm_atomic_helper_wait_for_flip_done [drm_kms_helper]] *ERROR* [CRTC:34:pipe A] flip_done timed out
Apr  1 21:52:52 HP-Compaq-6710b-GB889ET-ABE kernel: [  13.384046] ------------[ cut here ]------------
Apr  1 21:52:52 HP-Compaq-6710b-GB889ET-ABE kernel: [  13.384047] vblank wait timed out on crtc 0
Apr  1 21:52:52 HP-Compaq-6710b-GB889ET-ABE kernel: [  13.384120] WARNING: CPU: 0 PID: 91 at /build/linux-ZcR2Eb/linux-4.15.0/drivers/gpu/drm/drm_vblank.c:1081 drm_wait_one_vblank+0x188/0x190 [drm]

What do you think?

[SpAiK]

Ok, I just found the solution. Edit grub file (sudo nano  /etc/default/grub) and add "video = SVIDEO-1: d" to GRUB_CMDLINE_LINUX_DEFAULT.What I still don't understand is the root cause of this.

[trinidad]

The cause is Intel (incomplete firmware). This is an old bug started with kernel 4.8, (4.7 seems to have been OK) but I can't find any mention of it being fixed in newer kernels other than the workaround you used (disabling the s-video port). Seems it is still there (reported at RHEL & Debian) at least up through kernel 4.15. There may or may not be a kernel fix coming at some point. 

TC