drm/i915: hold forcewake around ring hw init

Empirical evidence suggests that we need to: On at least one ivb
machine when running the hangman i-g-t test, the rings don't properly
initialize properly - the RING_START registers seems to be stuck at
all zeros.

Holding forcewake around this register init sequences makes chip reset
reliable again. Note that this is not the first such issue:

commit f01db988ef6f6c70a6cc36ee71e4a98a68901229
Author: Sean Paul <seanpaul@chromium.org>
Date:   Fri Mar 16 12:43:22 2012 -0400

    drm/i915: Add wait_for in init_ring_common

added delay loops to make RING_START and RING_CTL initialization
reliable on the blt ring at boot-up. So I guess it won't hurt if we do
this unconditionally for all force_wake needing gpus.

To avoid copy&pasting of the HAS_FORCE_WAKE check I've added a new
intel_info bit for that.

v2: Fixup missing commas in static struct and properly handling the
error case in init_ring_common, both noticed by Jani Nikula.

Cc: stable@vger.kernel.org
Reported-and-tested-by: Yang Guang <guang.a.yang@intel.com>
Reviewed-by: Eugeni Dodonov <eugeni.dodonov@intel.com>
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=50522
Signed-Off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

1 files changed, 13 insertions, 3 deletions

diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.c b/drivers/gpu/drm/i915/intel_ringbuffer.c
index 9fbad086cb4b..e5b84ff89ca5 100644
--- a/drivers/gpu/drm/i915/intel_ringbuffer.c
+++ b/drivers/gpu/drm/i915/intel_ringbuffer.c
@@ -266,10 +266,15 @@ u32 intel_ring_get_active_head(struct intel_ring_buffer *ring)
 
 static int init_ring_common(struct intel_ring_buffer *ring)
 {
-        drm_i915_private_t *dev_priv = ring->dev->dev_private;
+        struct drm_device *dev = ring->dev;
+        drm_i915_private_t *dev_priv = dev->dev_private;
         struct drm_i915_gem_object *obj = ring->obj;
+        int ret = 0;
         u32 head;
 
+        if (HAS_FORCE_WAKE(dev))
+                gen6_gt_force_wake_get(dev_priv);
+
         /* Stop the ring if it's running. */
         I915_WRITE_CTL(ring, 0);
         I915_WRITE_HEAD(ring, 0);
@@ -317,7 +322,8 @@ static int init_ring_common(struct intel_ring_buffer *ring)
                                 I915_READ_HEAD(ring),
                                 I915_READ_TAIL(ring),
                                 I915_READ_START(ring));
-                return -EIO;
+                ret = -EIO;
+                goto out;
         }
 
         if (!drm_core_check_feature(ring->dev, DRIVER_MODESET))
@@ -329,7 +335,11 @@ static int init_ring_common(struct intel_ring_buffer *ring)
                 ring->last_retired_head = -1;
         }
 
-        return 0;
+out:
+        if (HAS_FORCE_WAKE(dev))
+                gen6_gt_force_wake_put(dev_priv);
+
+        return ret;
 }
 
 static int