drm/i915: Recompute WM when the cursor size changes

If the cursor width is changed, we may need to recompute our WM to
prevent untold flickering. We hope that the registers are flushed on the
same vblank to prevent underruns...

Cc: Damien Lespiau <damien.lespiau@intel.com>
Cc: Sagar Kamble <sagar.a.kamble@intel.com>
Signed-off-by: NChris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: NDamien Lespiau <damien.lespiau@intel.com>
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/intel_display.c

@@ -7745,6 +7745,7 @@ static int intel_crtc_cursor_set(struct drm_crtc *crtc,
 	struct drm_i915_private *dev_priv = dev->dev_private;
 	struct intel_crtc *intel_crtc = to_intel_crtc(crtc);
 	struct drm_i915_gem_object *obj;
+	unsigned old_width;
 	uint32_t addr;
 	int ret;
 
@@ -7835,13 +7836,18 @@ static int intel_crtc_cursor_set(struct drm_crtc *crtc,
 
 	mutex_unlock(&dev->struct_mutex);
 
+	old_width = intel_crtc->cursor_width;
+
 	intel_crtc->cursor_addr = addr;
 	intel_crtc->cursor_bo = obj;
 	intel_crtc->cursor_width = width;
 	intel_crtc->cursor_height = height;
 
-	if (intel_crtc->active)
+	if (intel_crtc->active) {
+		if (old_width != width)
+			intel_update_watermarks(crtc);
 		intel_crtc_update_cursor(crtc, intel_crtc->cursor_bo != NULL);
+	}
 
 	return 0;
 fail_unpin: