On Fri, Jan 11, 2013 at 09:53:53AM +0200, Jani Nikula wrote: > We stopped reading FORCEWAKE for posting reads in > > commit 8dee3eea3ccd3b6c00a8d3a08dd715d6adf737dd > Author: Ben Widawsky <ben at bwidawsk.net> > Date: Sat Sep 1 22:59:50 2012 -0700 > > drm/i915: Never read FORCEWAKE > > and started using something from the same cacheline instead. This was true > for ECOBUS, but not for GTFIFODBG. Add posting reads on ECOBUS where > GTFIFODBG was relied on. > > In true cargo cult spirit, add posting reads for FORCEWAKE_VLV writes as > well. > > Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=52411 > Reported-and-tested-by: Alexander Bersenev <bay at hackerdom.ru> > CC: Ben Widawsky <ben at bwidawsk.net> > Signed-off-by: Jani Nikula <jani.nikula at intel.com> Am I the only skeptic about what is actually fixing the bug here? Without WC MMIO, the cacheline we readback from makes no difference. ie. I put ECOBUS there for a warm and fuzzy feeling, nothing else. > --- > drivers/gpu/drm/i915/intel_pm.c | 17 ++++++++++++----- > 1 file changed, 12 insertions(+), 5 deletions(-) > > diff --git a/drivers/gpu/drm/i915/intel_pm.c b/drivers/gpu/drm/i915/intel_pm.c > index abfff29..06b75a1 100644 > --- a/drivers/gpu/drm/i915/intel_pm.c > +++ b/drivers/gpu/drm/i915/intel_pm.c > @@ -4122,7 +4122,8 @@ static void __gen6_gt_force_wake_get(struct drm_i915_private *dev_priv) > static void __gen6_gt_force_wake_mt_reset(struct drm_i915_private *dev_priv) > { > I915_WRITE_NOTRACE(FORCEWAKE_MT, _MASKED_BIT_DISABLE(0xffff)); > - POSTING_READ(ECOBUS); /* something from same cacheline, but !FORCEWAKE */ > + /* something from same cacheline, but !FORCEWAKE_MT */ > + POSTING_READ(ECOBUS); > } > > static void __gen6_gt_force_wake_mt_get(struct drm_i915_private *dev_priv) > @@ -4139,7 +4140,8 @@ static void __gen6_gt_force_wake_mt_get(struct drm_i915_private *dev_priv) > DRM_ERROR("Timed out waiting for forcewake old ack to clear.\n"); > > I915_WRITE_NOTRACE(FORCEWAKE_MT, _MASKED_BIT_ENABLE(FORCEWAKE_KERNEL)); > - POSTING_READ(ECOBUS); /* something from same cacheline, but !FORCEWAKE */ > + /* something from same cacheline, but !FORCEWAKE_MT */ > + POSTING_READ(ECOBUS); > > if (wait_for_atomic((I915_READ_NOTRACE(forcewake_ack) & 1), > FORCEWAKE_ACK_TIMEOUT_MS)) > @@ -4176,14 +4178,16 @@ void gen6_gt_check_fifodbg(struct drm_i915_private *dev_priv) > static void __gen6_gt_force_wake_put(struct drm_i915_private *dev_priv) > { > I915_WRITE_NOTRACE(FORCEWAKE, 0); > - /* gen6_gt_check_fifodbg doubles as the POSTING_READ */ > + /* something from same cacheline, but !FORCEWAKE */ > + POSTING_READ(ECOBUS); > gen6_gt_check_fifodbg(dev_priv); > } > > static void __gen6_gt_force_wake_mt_put(struct drm_i915_private *dev_priv) > { > I915_WRITE_NOTRACE(FORCEWAKE_MT, _MASKED_BIT_DISABLE(FORCEWAKE_KERNEL)); > - /* gen6_gt_check_fifodbg doubles as the POSTING_READ */ > + /* something from same cacheline, but !FORCEWAKE_MT */ > + POSTING_READ(ECOBUS); > gen6_gt_check_fifodbg(dev_priv); > } > > @@ -4223,6 +4227,8 @@ int __gen6_gt_wait_for_fifo(struct drm_i915_private *dev_priv) > static void vlv_force_wake_reset(struct drm_i915_private *dev_priv) > { > I915_WRITE_NOTRACE(FORCEWAKE_VLV, _MASKED_BIT_DISABLE(0xffff)); > + /* something from same cacheline, but !FORCEWAKE_VLV */ > + POSTING_READ(FORCEWAKE_ACK_VLV); > } > > static void vlv_force_wake_get(struct drm_i915_private *dev_priv) > @@ -4243,7 +4249,8 @@ static void vlv_force_wake_get(struct drm_i915_private *dev_priv) > static void vlv_force_wake_put(struct drm_i915_private *dev_priv) > { > I915_WRITE_NOTRACE(FORCEWAKE_VLV, _MASKED_BIT_DISABLE(FORCEWAKE_KERNEL)); > - /* The below doubles as a POSTING_READ */ > + /* something from same cacheline, but !FORCEWAKE_VLV */ > + POSTING_READ(FORCEWAKE_ACK_VLV); > gen6_gt_check_fifodbg(dev_priv); > } > > -- > 1.7.9.5 > -- Ben Widawsky, Intel Open Source Technology Center
