CHROMIUM: drm/i915: Improve RC6p stability

When the CPU is loaded and the GPU tries to switch RC6p modes, the GPU
sometimes gets stuck in RC6p mode and doesn't come out of it. I suspect
that our voltage rail is too weak and sometimes falls behind.

This change throttles down the number of RC6p transitions we do to appease it.

The change also disables clock gating which seems to help. Upstream commit
which does that is 0f846f81a154cc1818416918d22939bda73da194
(drm/i915: disable RCBP and VDS unit clock gating on SNB and VL)

I tested this on multiple Link machines for hours. The number of RC6 problems
went down from ~ one every 15 minutes to ~ one every 25 hours. So this is not
a complete solution, but I suspect there might be another, more difficult to
reproduce, problem. In any case it reduces the issue significantly, to the
point where we might be able to forget about it.

I measured the power usage on idle before/after this patch and saw no
difference. Obviously when the GPU load varies, it will consume more power
since it now takes more time to adapt.

Also note that not all machines seem to react equally. Some crash fairly
often, and some less often. So this will improve the situation to different
extents for different people.

BUG=chrome-os-partner:16886,chrome-os-partner:11474
TEST=ran the factory stress test (RunIn.Stress) on multiple Link machines for
TEST=about 100 hours, saw only 4 RC6 crashes.

Change-Id: I1135d90e2a155424388d23c6e0879a210b4a0146
Reviewed-on: https://gerrit.chromium.org/gerrit/42084
Tested-by: Stéphane Marchesin <marcheu@chromium.org>
Reviewed-by: Vincent Palatin <vpalatin@chromium.org>
Reviewed-by: Sameer Nanda <snanda@chromium.org>
Commit-Queue: Stéphane Marchesin <marcheu@chromium.org>

diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
index b76f292..6bfbd35 100644 (file)
--- a/drivers/gpu/drm/i915/intel_display.c
+++ b/drivers/gpu/drm/i915/intel_display.c
@@ -8338,7 +8338,7 @@ void gen6_enable_rps(struct drm_i915_private *dev_priv)
        I915_WRITE(GEN6_RC_SLEEP, 0);
        I915_WRITE(GEN6_RC1e_THRESHOLD, 1000);
        I915_WRITE(GEN6_RC6_THRESHOLD, 50000);
-       I915_WRITE(GEN6_RC6p_THRESHOLD, 100000);
+       I915_WRITE(GEN6_RC6p_THRESHOLD, 150000);
        I915_WRITE(GEN6_RC6pp_THRESHOLD, 64000); /* unused */
 
        rc6_mode = intel_enable_rc6(dev_priv->dev);
@@ -8361,7 +8361,7 @@ void gen6_enable_rps(struct drm_i915_private *dev_priv)
                   GEN6_RC_CTL_EI_MODE(1) |
                   GEN6_RC_CTL_HW_ENABLE);
 
-       I915_WRITE(GEN6_RP_DOWN_TIMEOUT, 10000);
+       I915_WRITE(GEN6_RP_DOWN_TIMEOUT, 1000000);
        I915_WRITE(GEN6_RP_INTERRUPT_LIMITS,
                   18 << 24 |
                   6 << 16);
@@ -8645,7 +8645,9 @@ static void ivybridge_init_clock_gating(struct drm_device *dev)
        /* According to the spec, bit 13 (RCZUNIT) must be set on IVB.
         * This implements the WaDisableRCZUnitClockGating workaround.
         */
-       I915_WRITE(GEN6_UCGCTL2, GEN6_RCZUNIT_CLOCK_GATE_DISABLE);
+       I915_WRITE(GEN6_UCGCTL2,
+                  GEN6_RCZUNIT_CLOCK_GATE_DISABLE |
+                  GEN6_RCCUNIT_CLOCK_GATE_DISABLE);
 
        I915_WRITE(ILK_DSPCLK_GATE, IVB_VRHUNIT_CLK_GATE);