On Tue, Mar 10, 2015 at 10:35:41AM +0000, Chris Wilson wrote: > On Tue, Mar 10, 2015 at 11:31:04AM +0100, Daniel Vetter wrote: > > On Fri, Feb 13, 2015 at 02:35:59PM +0000, Chris Wilson wrote: > > > Long ago I found that I was getting sporadic errors when booting SNB, > > > with the symptom being that the first batch died with IPEHR != *ACTHD, > > > typically caused by the TLB being invalid. These magically disappeared > > > if I held the forcewake during the entire ring initialisation sequence. > > > (It can probably be shortened to a short critical section, but the whole > > > initialisation is full of register writes and so we would be taking and > > > releasing forcewake almost continually, and so holding it over the > > > entire sequence will probably be a net win!) > > > > > > Note some of the kernels I encounted the issue already had the deferred > > > forcewake release, so it is still relevant. > > > > > > I know that there have been a few other reports with similar failure > > > conditions on SNB, I think such as > > > References: https://bugs.freedesktop.org/show_bug.cgi?id=80913 > > > > > > v2: Wrap i915_gem_init_hw() with its own security blanket as we take > > > that path following resume and reset. > > > > > > Signed-off-by: Chris Wilson <ch...@chris-wilson.co.uk> > > > --- > > > drivers/gpu/drm/i915/i915_gem.c | 18 ++++++++++++++++-- > > > 1 file changed, 16 insertions(+), 2 deletions(-) > > > > > > diff --git a/drivers/gpu/drm/i915/i915_gem.c > > > b/drivers/gpu/drm/i915/i915_gem.c > > > index 8d15c8110962..08450922f373 100644 > > > --- a/drivers/gpu/drm/i915/i915_gem.c > > > +++ b/drivers/gpu/drm/i915/i915_gem.c > > > @@ -4783,6 +4783,9 @@ i915_gem_init_hw(struct drm_device *dev) > > > if (INTEL_INFO(dev)->gen < 6 && !intel_enable_gtt()) > > > return -EIO; > > > > > > + /* Double layer security blanket, see i915_gem_init() */ > > > + intel_uncore_forcewake_get(dev_priv, FORCEWAKE_ALL); > > > + > > > if (dev_priv->ellc_size) > > > I915_WRITE(HSW_IDICR, I915_READ(HSW_IDICR) | IDIHASHMSK(0xf)); > > > > > > @@ -4815,7 +4818,7 @@ i915_gem_init_hw(struct drm_device *dev) > > > for_each_ring(ring, dev_priv, i) { > > > ret = ring->init_hw(ring); > > > if (ret) > > > - return ret; > > > + goto out; > > > } > > > > > > for (i = 0; i < NUM_L3_SLICES(dev); i++) > > > @@ -4832,9 +4835,11 @@ i915_gem_init_hw(struct drm_device *dev) > > > DRM_ERROR("Context enable failed %d\n", ret); > > > i915_gem_cleanup_ringbuffer(dev); > > > > > > - return ret; > > > + goto out; > > > } > > > > > > +out: > > > + intel_uncore_forcewake_put(dev_priv, FORCEWAKE_ALL); > > > return ret; > > > } > > > > > > @@ -4868,6 +4873,14 @@ int i915_gem_init(struct drm_device *dev) > > > dev_priv->gt.stop_ring = intel_logical_ring_stop; > > > } > > > > > > + /* This is just a security blanket to placate dragons. > > > + * On some systems, we very sporadically observe that the first TLBs > > > + * used by the CS may be stale, despite us poking the TLB reset. If > > > + * we hold the forcewake during initialisation these problems > > > + * just magically go away. > > > + */ > > > + intel_uncore_forcewake_get(dev_priv, FORCEWAKE_ALL); > > > > gem_init shouldn't ever touch the hw except through gem_init_hw. Do we > > really need the double-layer here? > > There are register accesses before, so yes since that's how I tested > it... > > > Also the forcewake hack in the ring > > init code should now be redundant, too. > > I am of the opinion that they still serve documentary value. Unless you > have an assert_force_wake() handy.
Ok, count me convinced. Reviewed-by: Daniel Vetter <daniel.vet...@ffwll.ch> And I guess this is for Jani + cc: stable. -Daniel -- Daniel Vetter Software Engineer, Intel Corporation +41 (0) 79 365 57 48 - http://blog.ffwll.ch _______________________________________________ Intel-gfx mailing list Intel-gfx@lists.freedesktop.org http://lists.freedesktop.org/mailman/listinfo/intel-gfx
