On Mon, Apr 2, 2012 at 11:48 AM, Daniel Vetter <daniel.vetter at ffwll.ch> wrote: > Inspired by the recent ppgtt regression report, where switching of > dmar only for the gpu seems to fix things completely, I've looked > again at the semaphores+vt-d situation. > > Contrary to my earlier testing a few months back my system is now > stable with dmar disabled for the igd, and not only when disabling > dmar completely. > > So I'm rather hopeful that all our recent fixes for snb have changed > things for code and it's time to try enabling semaphores again. We've > also had issues with enabling semaphores which are not vt-d related, > but I guess these are all fixed by the autoreport-disabling and lazy > request fix. And there's only one way to find out whether there are > still other issues ... > > Signed-Off-by: Daniel Vetter <daniel.vetter at ffwll.ch> > > --- > > If no further vt-d regressions show up in the 3.4 cycle I plan to > merge this into -next for 3.5 (in a month or so). Comments about how > unfeasibly you deem this highly welcome. > -Daniel > --- > ?drivers/gpu/drm/i915/i915_gem_execbuffer.c | ? ?8 +++++--- > ?1 files changed, 5 insertions(+), 3 deletions(-) > > diff --git a/drivers/gpu/drm/i915/i915_gem_execbuffer.c b/drivers/gpu/drm/i915/i915_gem_execbuffer.c > index 8e0b686..ac52433 100644 > --- a/drivers/gpu/drm/i915/i915_gem_execbuffer.c > +++ b/drivers/gpu/drm/i915/i915_gem_execbuffer.c > @@ -849,9 +849,11 @@ intel_enable_semaphores(struct drm_device *dev) > ? ? ? ?if (i915_semaphores >= 0) > ? ? ? ? ? ? ? ?return i915_semaphores; > > - ? ? ? /* Disable semaphores on SNB */ > - ? ? ? if (INTEL_INFO(dev)->gen == 6) > - ? ? ? ? ? ? ? return 0; > +#ifdef CONFIG_INTEL_IOMMU > + ? ? ? /* Disable semaphores on SNB if VT-d is on. */ > + ? ? ? if (INTEL_INFO(dev)->gen == 6 && intel_iommu_gfx_mapped) > + ? ? ? ? ? ? ? return false; It might be nice to have a printk here giving instructions for how to work around this. For example: i915: Disabling semaphores to work around a DMAR issue. As an alternative, boot with intel_iommu=igfx_off [or on, igfx_off, or whatever it's supposed to be]. The documentation in kernel-parameters.txt is at best unclear to the uninitiated. --Andy
