i915: when kgdb is active display compression should be off

If the HW compression is left on, the call backs from the HW will
crash the kernel.  The only time this code is called is when kernel
mode setting is in use with kgdb and the kdb shell.

The atomic display pipe handler callback will reset everything when
kgdb restores kernel to the run state.
Signed-off-by: NJason Wessel <jason.wessel@windriver.com>
Acked-by: NJesse Barnes <jbarnes@virtuousgeek.org>
CC: David Airlie <airlied@linux.ie>

drivers/gpu/drm/i915/intel_display.c

@@ -1251,6 +1251,10 @@ static void intel_update_fbc(struct drm_crtc *crtc,
 		goto out_disable;
 	}
 
+	/* If the kernel debugger is active, always disable compression */
+	if (in_dbg_master())
+		goto out_disable;
+
 	if (intel_fbc_enabled(dev)) {
 		/* We can re-enable it in this case, but need to update pitch */
 		if ((fb->pitch > dev_priv->cfb_pitch) ||