drm/i915: add timeout to FBC disable waits

FBC disable on 965 can take long enough to trigger latency checks in the
kernel so be sure to timeout after a reasonable period.

Fixes https://bugzilla.kernel.org/show_bug.cgi?id=15015.

Tested-by: James Ettle <theholyettlz@googlemail.com>
Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>
Signed-off-by: Eric Anholt <eric@anholt.net>

1 files changed, 11 insertions, 2 deletions

diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
index b867f3c78408..36afe9409964 100644
--- a/drivers/gpu/drm/i915/intel_display.c
+++ b/drivers/gpu/drm/i915/intel_display.c
@@ -1029,19 +1029,28 @@ static void i8xx_enable_fbc(struct drm_crtc *crtc, unsigned long interval)
 void i8xx_disable_fbc(struct drm_device *dev)
 {
         struct drm_i915_private *dev_priv = dev->dev_private;
+        unsigned long timeout = jiffies + msecs_to_jiffies(1);
         u32 fbc_ctl;
 
         if (!I915_HAS_FBC(dev))
                 return;
 
+        if (!(I915_READ(FBC_CONTROL) & FBC_CTL_EN))
+                return; /* Already off, just return */
+
         /* Disable compression */
         fbc_ctl = I915_READ(FBC_CONTROL);
         fbc_ctl &= ~FBC_CTL_EN;
         I915_WRITE(FBC_CONTROL, fbc_ctl);
 
         /* Wait for compressing bit to clear */
-        while (I915_READ(FBC_STATUS) & FBC_STAT_COMPRESSING)
-                ; /* nothing */
+        while (I915_READ(FBC_STATUS) & FBC_STAT_COMPRESSING) {
+                if (time_after(jiffies, timeout)) {
+                        DRM_DEBUG_DRIVER("FBC idle timed out\n");
+                        break;
+                }
+                ; /* do nothing */
+        }
 
         intel_wait_for_vblank(dev);