drm/i915: Delay the release of the forcewake by a jiffie

Obtaining the forcwake requires expensive and time consuming
serialisation. And we often try to obtain the forcewake multiple times
in very quick succession. We can reduce the overhead of these sequences
by delaying the forcewake release, and so not hammer the hw quite so
hard.

I was hoping this would help with the spurious
[drm:__gen6_gt_force_wake_mt_get] *ERROR* Timed out waiting for forcewake old ack to clear.
found on Haswell. Alas not.

v2: Fix teardown ordering - unmap the regs after turning off forcewake,
and make sure we do turn off forcewake - both found by Ville.

v3: As we introduce intel_uncore_fini(), use it to make sure everything
is disabled before we hand back to the BIOS.

Note: I have no claims for improved performance, stablity or power
comsumption for this patch. We should not be hitting the registers often
enough for this to improve benchmarks, but given the nature of our hw it
is likely to improve long term stability.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

1 files changed, 3 insertions, 0 deletions

diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
index bbe889dfc0ff..662c0ff0b049 100644
--- a/drivers/gpu/drm/i915/i915_drv.h
+++ b/drivers/gpu/drm/i915/i915_drv.h
@@ -408,6 +408,8 @@ struct intel_uncore {
 
         unsigned fifo_count;
         unsigned forcewake_count;
+
+        struct delayed_work force_wake_work;
 };
 
 #define DEV_INFO_FOR_EACH_FLAG(func, sep) \
@@ -1801,6 +1803,7 @@ extern void intel_uncore_early_sanitize(struct drm_device *dev);
 extern void intel_uncore_init(struct drm_device *dev);
 extern void intel_uncore_clear_errors(struct drm_device *dev);
 extern void intel_uncore_check_errors(struct drm_device *dev);
+extern void intel_uncore_fini(struct drm_device *dev);
 
 void
 i915_enable_pipestat(drm_i915_private_t *dev_priv, int pipe, u32 mask);