Comment 93 for bug 311895

Created an attachment (id=24465)
debug logs for monitor/VT state changes

Ah, I know what changed. After a clean boot, with the latest (version 5) patch applied, everything works perfectly for me, the trouble starts when I switch off my monitor, and switch it on again (as I usually do during lunch break).

So I looked at dmesg, Xorg log, and registers in three states.

1. After clean boot, and GNOME login. See boot.* files.

2. Switch to VT1 and back. dmesg says

  [drm:i915_get_vblank_counter] *ERROR* trying to get vblank count for disabled pipe 1

   Registers are wildly different, see diff -U0 boot.registers.txt vtsiwtch.registers.txt. After waiting for one minute, the registers change further to

-(II): FBC_STATUS: 0x20000000
+(II): FBC_STATUS: 0x60000000

  Xorg log gets a some 30 lines of info lines, and some interesting warnings:

$ diff -u boot.Xorg.log vtswitch.Xorg.log | grep -v '(II)'
+(WW) intel(0): ESR is 0x00000001, instruction error
+(WW) intel(0): Existing errors found in hardware state.
+(WW) intel(0): plane B needs more FIFO entries

3. Switch off monitor, and turn it on again. Now I get the occasional flickering.

  dmesg gets some USB disconnect/connect messages (monitor has USB hub with some stuff), nothing X related.

  registers do not change at all.

  No new Xorg log entries.

Now, having typed this, it seems to me that switching off the monitor doesn't change much, and that most likely the VT switch is to blame; I will do another test to affirm that I get flickering after VT switch already (I'll report back if that is not the case). Your patch seems to work by and large, but seems to not take VT switches into account correctly.