Created attachment 143003 [details]
dmesg log with drm.debug=0xe
As outlined in https://lkml.org/lkml/2019/1/4/611 , I experienced a significant increase in boot time after moving from kernel 4.19.12 to 4.20. The hardware is a Asus K53SV with a i7-2630QM (Sandy Bridge) with an external display connected via HDMI.
Bisecting the commits revealed 516a49cc19467e298d08a404f73a6e311f4548d1 as the cause.
The requested dmesg log with drm.debug=0xe is attached to this ticket.
The hardware seems to be in a rather weird state when the driver loads. The PLL is on but apparently misconfigured, DP-C is on but not attached to the right pipe, etc.
Please reboot without loading i915, then run 'intel_reg dump > regdump' (intel_reg comes from igt-gpu-tools), and attach the results here.
Created attachment 143017 [details]
Output of intel_reg dump without i915 loaded
Here's the register dump that was taken without i915 loaded, with the monitor attached (but no signal being output), the laptop display turned off, and kernel running in runlevel 1.
If it helps, the monitor in question is a Dell U2515H whose native resolution is 2560x1440, which is probably reported in the EDID. The maximum resolution supported by this chip is supposedly 1080p, though I have no problems with running my desktop in 1440p@44 with a custom modeline specified in Xorg.conf.
The warning messages visible in the kernel output (attached earlier) also appeared on the old kernel version, and didn't seem to cause any trouble besides being there.
Created attachment 143020 [details] [review]
[PATCH] drm/i915: Try to sanitize bogus DPLL state left over by broken SNB BIOSen
I think this ought to work around the problem. It's not ideal though since we still get a bunch of WARNs.
As mentioned in the patch I think this same problem was seen on some other SNB machine years ago, but it got fixed by a BIOS update. Sadly looks like your machine doesn't have that option (unless I missed something on the ASUS website).
Please test and let me know whether this helps.
Works great for me! The boot time, and the messages, are back to what they were in 4.19.12.
I applied the patch on top of 5.0-rc1 and only had to change IS_GEN(dev_priv, 6) to IS_GEN6(dev_priv) which I hope does the same thing.
Unfortunately, you're right about the BIOS : I'm running the latest revision, which has not been updated since 2011.
Thanks for getting this sorted out so quickly.