[Intel-gfx] [PATCH 2/2] drm/i915: enable plain RC6 on Sandy Bridge by default

[Eugeni Dodonov]

This is yet another chapter in the ongoing saga of bringing RC6 to Sandy
Bridge machines by default.

Now that we have discovered that RC6 issues are triggered by RC6+ state,
let's try to disable it by default. Plain RC6 is the one responsible for
most energy savings, and so far it haven't given any problems - at least,
none we are aware of.

So with this, when i915_enable_rc6=-1 (e.g., the default value), we'll
attempt to enable plain RC6 only on SNB. For Ivy Bridge, the behavior
stays the same as always - we enable both RC6 and deep RC6.

Note that while this exact patch does not has explicit tested-by's, the
equivalent settings were fixed in 3.3 kernel by a smaller patch. And it
has also received considerable testing through Canonical RC6 task-force
testing at https://wiki.ubuntu.com/Kernel/PowerManagementRC6. Up to date,
it looks like all the known issues are gone.

v2: improve description and reference a couple of open bugs related to
RC6 which seem to be fixed with this change.

References: https://bugs.freedesktop.org/show_bug.cgi?id=41682
References: https://bugs.freedesktop.org/show_bug.cgi?id=38567
References: https://bugs.freedesktop.org/show_bug.cgi?id=44867
Signed-off-by: Eugeni Dodonov <eugeni.dodonov at intel.com>
---
 drivers/gpu/drm/i915/intel_display.c |    8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
index c6d8bc4..dcae2c9 100644
--- a/drivers/gpu/drm/i915/intel_display.c
+++ b/drivers/gpu/drm/i915/intel_display.c
@@ -8233,11 +8233,11 @@ static int intel_enable_rc6(struct drm_device *dev)
 	 * Disable rc6 on Sandybridge
 	 */
 	if (INTEL_INFO(dev)->gen == 6) {
-		DRM_DEBUG_DRIVER("Sandybridge: RC6 disabled\n");
-		return 0;
+		DRM_DEBUG_DRIVER("Sandybridge: deep RC6 disabled\n");
+		return INTEL_RC6_ENABLE;
 	}
-	DRM_DEBUG_DRIVER("RC6 enabled\n");
-	return 1;
+	DRM_DEBUG_DRIVER("RC6 and deep RC6 enabled\n");
+	return (INTEL_RC6_ENABLE | INTEL_RC6p_ENABLE);
 }
 
 void gen6_enable_rps(struct drm_i915_private *dev_priv)
-- 
1.7.9.4