drm/i915: Initialise g4x watermarks for disabled pipes

We were using uninitialised watermarks values for disabled pipes which
were combined into a single WM register and so corrupting the values for
the enabled pipe and upsetting the display hardware.

Reported-by: Riccardo Magliocchetti <riccardo.magliocchetti@gmail.com>
Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=32612
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Keith Packard <keithp@keithp.com>

1 files changed, 4 insertions, 1 deletions

diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
index 4fc21e047a2..e522c702b04 100644
--- a/drivers/gpu/drm/i915/intel_display.c
+++ b/drivers/gpu/drm/i915/intel_display.c
@@ -3771,8 +3771,11 @@ static bool g4x_compute_wm0(struct drm_device *dev,
         int entries, tlb_miss;
 
         crtc = intel_get_crtc_for_plane(dev, plane);
-        if (crtc->fb == NULL || !crtc->enabled)
+        if (crtc->fb == NULL || !crtc->enabled) {
+                *cursor_wm = cursor->guard_size;
+                *plane_wm = display->guard_size;
                 return false;
+        }
 
         htotal = crtc->mode.htotal;
         hdisplay = crtc->mode.hdisplay;