[Intel-gfx] [PATCH 4/4] drm/i915: optional fewer warning patch

[Ben Widawsky]

This patch will likely produce much fewer warnings, but perhaps hide
some bugs in the driver. I believe it's a good starting point however to
find the really serious issues first.

Goal is to hide warnings if the refcount for the forcewake "lock" is not
zero

Signed-off-by: Ben Widawsky <ben at bwidawsk.net>
---
 drivers/gpu/drm/i915/i915_drv.c |   14 ++++++++++----
 1 files changed, 10 insertions(+), 4 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_drv.c b/drivers/gpu/drm/i915/i915_drv.c
index fcd5c9a..33341d4 100644
--- a/drivers/gpu/drm/i915/i915_drv.c
+++ b/drivers/gpu/drm/i915/i915_drv.c
@@ -286,9 +286,14 @@ void gen6_gt_force_wake_get(struct drm_i915_private *dev_priv)
 	 * immediately. Not having the lock causes a race, but all bets are off
 	 * when using forced forcewake, which should only be touched through
 	 * root-only entry in debugfs.
+	 *
+	 * Intelligent users of the interface may do a force_wake_get() followed
+	 * by many register reads and writes, knowing that the reference count
+	 * is already incremented. So we do not want to warn on those.
 	 */
-	WARN_ON(!mutex_is_locked(&dev_priv->dev->struct_mutex) &&
-		!atomic_read(&dev_priv->forcewake_force));
+	WARN_ON((!mutex_is_locked(&dev_priv->dev->struct_mutex) &&
+		 !dev_priv->forcewake_count) &&
+		 !atomic_read(&dev_priv->forcewake_force));
 
 	if (dev_priv->forcewake_count++ == 0)
 		__gen6_gt_force_wake_get(dev_priv);
@@ -302,8 +307,9 @@ static void __gen6_gt_force_wake_put(struct drm_i915_private *dev_priv)
 
 void gen6_gt_force_wake_put(struct drm_i915_private *dev_priv)
 {
-	WARN_ON(!mutex_is_locked(&dev_priv->dev->struct_mutex) &&
-		!atomic_read(&dev_priv->forcewake_force));
+	WARN_ON((!mutex_is_locked(&dev_priv->dev->struct_mutex) &&
+		 !dev_priv->forcewake_count) &&
+		 !atomic_read(&dev_priv->forcewake_force));
 
 	if (--dev_priv->forcewake_count == 0)
 		__gen6_gt_force_wake_put(dev_priv);
-- 
1.7.3.4