drm/i915/overlay: Workaround i830 overlay activation bug.

On i830, there exists a bug where an overlay on pipe B requires the mode
clock on pipe A in order to activate. So workaround this by activating
pipe A when trying to enable the overlay on pipe B.

References:

  [Bug 29007] GPU hang on video playback with overlay
  https://bugs.freedesktop.org/show_bug.cgi?id=29007

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>

drivers/gpu/drm/i915/intel_overlay.c

@@ -243,18 +243,76 @@ static int intel_overlay_do_wait_request(struct intel_overlay *overlay,
 	return 0;
 }
 
+/* Workaround for i830 bug where pipe a must be enable to change control regs */
+static int
+i830_activate_pipe_a(struct drm_device *dev)
+{
+	drm_i915_private_t *dev_priv = dev->dev_private;
+	struct intel_crtc *crtc;
+	struct drm_crtc_helper_funcs *crtc_funcs;
+	struct drm_display_mode vesa_640x480 = {
+		DRM_MODE("640x480", DRM_MODE_TYPE_DRIVER, 25175, 640, 656,
+			 752, 800, 0, 480, 489, 492, 525, 0,
+			 DRM_MODE_FLAG_NHSYNC | DRM_MODE_FLAG_NVSYNC)
+	}, *mode;
+
+	crtc = to_intel_crtc(dev_priv->pipe_to_crtc_mapping[0]);
+	if (crtc->dpms_mode == DRM_MODE_DPMS_ON)
+		return 0;
+
+	/* most i8xx have pipe a forced on, so don't trust dpms mode */
+	if (I915_READ(PIPEACONF) & PIPEACONF_ENABLE)
+		return 0;
+
+	crtc_funcs = crtc->base.helper_private;
+	if (crtc_funcs->dpms == NULL)
+		return 0;
+
+	DRM_DEBUG_DRIVER("Enabling pipe A in order to enable overlay\n");
+
+	mode = drm_mode_duplicate(dev, &vesa_640x480);
+	drm_mode_set_crtcinfo(mode, CRTC_INTERLACE_HALVE_V);
+	if(!drm_crtc_helper_set_mode(&crtc->base, mode,
+				       crtc->base.x, crtc->base.y,
+				       crtc->base.fb))
+		return 0;
+
+	crtc_funcs->dpms(&crtc->base, DRM_MODE_DPMS_ON);
+	return 1;
+}
+
+static void
+i830_deactivate_pipe_a(struct drm_device *dev)
+{
+	drm_i915_private_t *dev_priv = dev->dev_private;
+	struct drm_crtc *crtc = dev_priv->pipe_to_crtc_mapping[0];
+	struct drm_crtc_helper_funcs *crtc_funcs = crtc->helper_private;
+
+	crtc_funcs->dpms(crtc, DRM_MODE_DPMS_OFF);
+}
+
 /* overlay needs to be disable in OCMD reg */
 static int intel_overlay_on(struct intel_overlay *overlay)
 {
 	struct drm_device *dev = overlay->dev;
 	struct drm_i915_gem_request *request;
+	int pipe_a_quirk = 0;
+	int ret;
 
 	BUG_ON(overlay->active);
 	overlay->active = 1;
 
+	if (IS_I830(dev)) {
+		pipe_a_quirk = i830_activate_pipe_a(dev);
+		if (pipe_a_quirk < 0)
+			return pipe_a_quirk;
+	}
+
 	request = kzalloc(sizeof(*request), GFP_KERNEL);
-	if (request == NULL)
-		return -ENOMEM;
+	if (request == NULL) {
+		ret = -ENOMEM;
+		goto out;
+	}
 
 	BEGIN_LP_RING(4);
 	OUT_RING(MI_OVERLAY_FLIP | MI_OVERLAY_ON);
@@ -263,8 +321,13 @@ static int intel_overlay_on(struct intel_overlay *overlay)
 	OUT_RING(MI_NOOP);
 	ADVANCE_LP_RING();
 
-	return intel_overlay_do_wait_request(overlay, request, true,
-					     NEEDS_WAIT_FOR_FLIP);
+	ret = intel_overlay_do_wait_request(overlay, request, true,
+					    NEEDS_WAIT_FOR_FLIP);
+out:
+	if (pipe_a_quirk)
+		i830_deactivate_pipe_a(dev);
+
+	return ret;
 }
 
 /* overlay needs to be enabled in OCMD reg */