Re: kern/49875 (kernel crash with i915drmkms on Intel 82855GM)

[Izumi Tsutsui <tsutsui%ceres.dti.ne.jp@localhost>]

The following reply was made to PR kern/49875; it has been noted by GNATS.

From: Izumi Tsutsui <tsutsui%ceres.dti.ne.jp@localhost>
To: riastradh%NetBSD.org@localhost
Cc: gnats-bugs%NetBSD.org@localhost, tsutsui%ceres.dti.ne.jp@localhost
Subject: Re: kern/49875 (kernel crash with i915drmkms on Intel 82855GM)
Date: Sun, 26 Jul 2015 16:08:38 +0900

 > We can apply the change, although it's not clear to me that that fixes
 > whatever the real problem here is.
 
 - The real problem is kernel panic (NULL pointer dereference?)
   in i915_gem_object_pin_to_display_plane() on starting Xserver
 
 > Does X successfully start -- with
 > an apparently harmless warning in dmesg -- or does it fail in some
 > other way with the change?
 
 - With the upstream change X successfully starts with warnings
   (at least no kernel panic)
 - The warnings are not stable:
  - On the first startup
    "DRM error in intel_pipe_set_base: pin & fence failed"
  - On the second (and further) startups
    "DRM error in i8xx_irq_handler: pipe B underrun"
 - Xserver sometimes renders garbages and hangs when
   multiple heavy GTK applications (firefox + mikutter etc.)
   are running
   (I'm not sure if this is 855GM specific or not, though)
 
 In short word, "the upstream fix is not perfect but much better".
 
 ---
 Izumi Tsutsui