[Intel-gfx] [PATCH] drm/i915: use hsw rps tuning values everywhere on gen6+

[Daniel Vetter]

James Bottomley reported [1] a massive power regression, due to the
enabling of semaphores by default in 3.5. A workaround for him is to
again disable semaphores. And indeed, his system has a very hard time
to entre rc6 with semaphores enabled.

Ben Widawsky run around with a kill-a-watt a lot and noticed:
- There are indeed a few rare systems that seem to have a hard time
  entering rc6 when desktop-idle.
- One machine, The Indestructible Toshiba regressed in this behaviour
  between 3.5 and 3.6 in a merge commit! So rc6 behaviour with the
  current setting seems to be highly timing dependent and not robust
  at all.
- The behaviour James reported wrt semaphores seems to be a freak
  timing thing that only happens on his specific machine, confirming
  that enabling semaphores shouldn't reduce rc6 residency.

Now furthermore the Google ChromeOS guys reported [2] a while ago that
at least on some machines a simply a blinking cursor can keep the gpu
turbo at the highest frequency. This is because the current rps limits
used on snb/ivb are highly asymmetric.

On the theory that gpu turbo and rc6 tuning values are related, we've
tried whether the much saner looking (since much less asymmetric) rps
tuning values used for hsw would also help entering rc6 more robustly.

And it seems to work.

v2: Testing on James Bottemly's funky machine indicates that the
Haswell values are not aggressive enough. And testing from the Google
ChromeOS team indicates that we actually want symmetric values for the
most power savings. So let's try that.

Reference[1]: http://lists.freedesktop.org/archives/dri-devel/2012-July/025675.html
Reference[2]: http://lists.freedesktop.org/archives/intel-gfx/2012-July/018692.html
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=53393
Tested-by: Ben Widawsky <ben at bwidawsk.net>
Cc: stable at vger.kernel.org
Signed-off-by: Daniel Vetter <daniel.vetter at ffwll.ch>
---
 drivers/gpu/drm/i915/intel_pm.c |   15 ++++-----------
 1 file changed, 4 insertions(+), 11 deletions(-)

diff --git a/drivers/gpu/drm/i915/intel_pm.c b/drivers/gpu/drm/i915/intel_pm.c
index 58c07cd..314da5c 100644
--- a/drivers/gpu/drm/i915/intel_pm.c
+++ b/drivers/gpu/drm/i915/intel_pm.c
@@ -2441,17 +2441,10 @@ static void gen6_enable_rps(struct drm_device *dev)
 		   dev_priv->max_delay << 24 |
 		   dev_priv->min_delay << 16);
 
-	if (IS_HASWELL(dev)) {
-		I915_WRITE(GEN6_RP_UP_THRESHOLD, 59400);
-		I915_WRITE(GEN6_RP_DOWN_THRESHOLD, 245000);
-		I915_WRITE(GEN6_RP_UP_EI, 66000);
-		I915_WRITE(GEN6_RP_DOWN_EI, 350000);
-	} else {
-		I915_WRITE(GEN6_RP_UP_THRESHOLD, 10000);
-		I915_WRITE(GEN6_RP_DOWN_THRESHOLD, 1000000);
-		I915_WRITE(GEN6_RP_UP_EI, 100000);
-		I915_WRITE(GEN6_RP_DOWN_EI, 5000000);
-	}
+	I915_WRITE(GEN6_RP_UP_THRESHOLD, 59400);
+	I915_WRITE(GEN6_RP_DOWN_THRESHOLD, 59400);
+	I915_WRITE(GEN6_RP_UP_EI, 66000);
+	I915_WRITE(GEN6_RP_DOWN_EI, 350000);
 
 	I915_WRITE(GEN6_RP_IDLE_HYSTERSIS, 10);
 	I915_WRITE(GEN6_RP_CONTROL,
-- 
1.7.10.4