On Fri, Oct 30, 2015 at 04:58:41PM +0000, Chris Wilson wrote: > On Fri, Oct 30, 2015 at 05:14:21PM +0100, Daniel Vetter wrote: > > On Fri, Oct 23, 2015 at 06:43:32PM +0100, Chris Wilson wrote: > > > When accessing through the GTT from one CPU whilst concurrently updating > > > the GGTT PTEs in another thread, the hardware likes to return random > > > data. As we have strong serialisation prevent us from modifying the PTE > > > of an active GTT mmapping, we have to conclude that it whilst modifying > > > other PTE's that error occurs. (I have not looked for any pattern such > > > as modifying PTE within the same page or cacheline as active PTE - > > > though checking whether revoking neighbouring objects should be enough > > > to test that theory.) The corruption also seems restricted to Braswell > > > and disappears with maxcpus=0. This patch stops all access through the > > > GTT by other CPUs when we update any PTE by stopping the machine around > > > the GGTT update. > > > > > > Testcase: igt/gem_concurrent_blit > > > Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=89079 > > > Signed-off-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx> > > > > Wild guess, since it wouldn't be the first time hw engineers screwed this > > up. > > > > Cheers, Daniel > > > > diff --git a/drivers/gpu/drm/i915/i915_gem_gtt.c b/drivers/gpu/drm/i915/i915_gem_gtt.c > > index d1c5cf89fe77..de983c8e6e54 100644 > > --- a/drivers/gpu/drm/i915/i915_gem_gtt.c > > +++ b/drivers/gpu/drm/i915/i915_gem_gtt.c > > @@ -2337,12 +2337,8 @@ int i915_gem_gtt_prepare_object(struct drm_i915_gem_object *obj) > > > > static void gen8_set_pte(void __iomem *addr, gen8_pte_t pte) > > { > > -#ifdef writeq > > - writeq(pte, addr); > > -#else > > iowrite32((u32)pte, addr); > > iowrite32(pte >> 32, addr + 4); > > -#endif > > Tried: > static void gen8_set_pte(void __iomem *addr, gen8_pte_t pte) > { > -#ifdef writeq > - writeq(pte, addr); > -#else > - iowrite32((u32)pte, addr); > - iowrite32(pte >> 32, addr + 4); > -#endif > + iowrite32(0, addr); > + wmb(); > + iowrite32(upper_32_bits(pte), addr + 4); > + iowrite32(lower_32_bits(pte), addr); > + wmb(); > } > > and just the plain iowrite(lower), iowrite(upper), neither helps. Added a note about this and applied to dinq. Yay for awesome hw. Thanks, Daniel -- Daniel Vetter Software Engineer, Intel Corporation http://blog.ffwll.ch _______________________________________________ Intel-gfx mailing list Intel-gfx@xxxxxxxxxxxxxxxxxxxxx http://lists.freedesktop.org/mailman/listinfo/intel-gfx
