From 078595043b490a5cf0c272fe90151be9a5d48973 Mon Sep 17 00:00:00 2001 From: Mika Kuoppala Date: Wed, 28 Jan 2015 15:25:05 +0200 Subject: [PATCH] drm/i915: Don't do posting reads on getting forcewake MIME-Version: 1.0 Content-Type: text/plain; charset=utf8 Content-Transfer-Encoding: 8bit The checking for ack and also any subsequent mmio access will serialize with setting the forcewake bit. Drop the posting read as superfluous. Note that in the put side we still want to keep the posting read as it will ensure that the hw sees our forcewake release in a timely manner and doesn't keep the hw powered up. Comment from Chris: On Wed, Jan 28, 2015 at 05:54:14PM +0200, Mika Kuoppala wrote: > Ville Syrjälä writes: > > IIRC the posting read from same cache line actually fixed real bugs. So > > I'm a bit worried about dropping them. But I suppose it's possible only > > the _put side was important for those bugs. > > I found these: > > commit 6af2d180f82151cf3d58952e35a4f96e45bc453a > Author: Daniel Vetter > Date: Thu Jul 26 16:24:50 2012 +0200 > > drm/i915: fix forcewake related hangs on snb > > commit 8dee3eea3ccd3b6c00a8d3a08dd715d6adf737dd > Author: Ben Widawsky > Date: Sat Sep 1 22:59:50 2012 -0700 > > drm/i915: Never read FORCEWAKE > > https://bugs.freedesktop.org/show_bug.cgi?id=51738 > https://bugs.freedesktop.org/show_bug.cgi?id=52424 > > The snb here seems to survive gem_dummy_reloc_loop and > gem_ring_sync_loop in here with the get side posting removed. Note that we kept the once associated with #52424, but judging by my comments in #51738 the posting read is just a band aid anyway as a full mb() itself was not adequate. Suggested-by: Chris Wilson Signed-off-by: Mika Kuoppala Reviewed-by: Chris Wilson [danvet: paste relevant review discussion in.] Signed-off-by: Daniel Vetter --- drivers/gpu/drm/i915/intel_uncore.c | 1 - 1 file changed, 1 deletion(-) diff --git a/drivers/gpu/drm/i915/intel_uncore.c b/drivers/gpu/drm/i915/intel_uncore.c index be2c7fcf5f1f..76b60a3538b2 100644 --- a/drivers/gpu/drm/i915/intel_uncore.c +++ b/drivers/gpu/drm/i915/intel_uncore.c @@ -131,7 +131,6 @@ fw_domains_get(struct drm_i915_private *dev_priv, enum forcewake_domains fw_doma for_each_fw_domain_mask(d, fw_domains, dev_priv, id) { fw_domain_wait_ack_clear(d); fw_domain_get(d); - fw_domain_posting_read(d); fw_domain_wait_ack(d); } } -- 2.20.1