drm/i915: fixup forcewake spinlock fallout in drpc debugfs function

My forcewake spinlock patches have a functional conflict with Ben
Widawsky's gen6 drpc support for debugfs. Result was a benign warning
about trying to read an non-atomic variabla with atomic_read.

Note that the entire check is racy anyway and purely informational.
Also update it to reflect the forcewake voodoo changes, the kernel can
now also hold onto a forcewake reference for longer times.

Signed-Off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Reviewed-by: Ben Widawsky <ben@bwidawsk.net>
Signed-off-by: Keith Packard <keithp@keithp.com>

1 files changed, 8 insertions, 3 deletions

diff --git a/drivers/gpu/drm/i915/i915_debugfs.c b/drivers/gpu/drm/i915/i915_debugfs.c
index 99f140798808..deaa657292b4 100644
--- a/drivers/gpu/drm/i915/i915_debugfs.c
+++ b/drivers/gpu/drm/i915/i915_debugfs.c
@@ -1075,6 +1075,7 @@ static int gen6_drpc_info(struct seq_file *m)
         struct drm_device *dev = node->minor->dev;
         struct drm_i915_private *dev_priv = dev->dev_private;
         u32 rpmodectl1, gt_core_status, rcctl1;
+        unsigned forcewake_count;
         int count=0, ret;
 
 
@@ -1082,9 +1083,13 @@ static int gen6_drpc_info(struct seq_file *m)
         if (ret)
                 return ret;
 
-        if (atomic_read(&dev_priv->forcewake_count)) {
-                seq_printf(m, "RC information inaccurate because userspace "
-                              "holds a reference \n");
+        spin_lock_irq(&dev_priv->gt_lock);
+        forcewake_count = dev_priv->forcewake_count;
+        spin_unlock_irq(&dev_priv->gt_lock);
+
+        if (forcewake_count) {
+                seq_printf(m, "RC information inaccurate because somebody "
+                              "holds a forcewake reference \n");
         } else {
                 /* NB: we cannot use forcewake, else we read the wrong values */
                 while (count++ < 50 && (I915_READ_NOTRACE(FORCEWAKE_ACK) & 1))