pi4/fkms: boot fails due to flip_done timed out (now 1080p and lower)

[alanbork]

under f29ab05611eef385d17675c77190df0b87a0d456, I can't get the pi4 to fully boot with fkms enabled. that is to say it boots but the screen shuts down mid-boot and the machine becomes so unresponsive that I frequently can't ssh in.

it's failing just like it used to for 4k resolutions (#4271), with a

[ 798.560610] [drm:drm_atomic_helper_wait_for_flip_done [drm_kms_helper]] ERROR [CRTC:87:crtc-0] flip_done timed out

but now:

• overclocking doesn't help
• using a lower resolution doesn't help (1080p, 480p; I haven't tried that many since it's so hard to recover from this with SSH unresponsive)

revert to 039088f7d929b0d1cc49e8d2012df0652f908518 and it boots with no problems.

config.txt:

dtoverlay=vc4-fkms-v3d
max_framebuffers=1
hdmi_force_hotplug=1
hdmi_group=1
hdmi_mode=16
hdmi_enable_4kp60=1

WRT overclocking, and unlike the 4k issue, adding these lines don't help:

#overclcking option can be toggled on of off, no change 
core_freq=600
core_freq_min=600

[popcornmix]

Can you try with latest rpi-update kernel?

[alanbork]

did rpi-update 9dbcd6dfed16cc7de4a67b9ca445c4847f68c4c2

working now at 1080p, also 3840x2160-60.00hz(60).