drm/i915: Reduce the time we hold struct mutex in intel_pipe_set_base()

We don't need to hold struct_mutex all through intel_pipe_set_base(),
just need to hold it while pinning/unpinning the buffers.

So reduce the struct_mutext usage in intel_pipe_set_base() just like we
did for the sprite code in:
 commit 82284b6becdbef6d8cd3fb43e8698510833a5129
 Author: Ville Syrjälä <ville.syrjala@linux.intel.com>
 Date:   Tue Oct 1 18:02:12 2013 +0300

    drm/i915: Reduce the time we hold struct mutex in sprite update_plane code

The FBC and PSR locking is still entirely fubar. That stuff was
previouly done while holding struct_mutex, so leave it there for now.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/intel_display.c

@@ -2477,8 +2477,8 @@ intel_pipe_set_base(struct drm_crtc *crtc, int x, int y,
 	ret = intel_pin_and_fence_fb_obj(dev,
 					 to_intel_framebuffer(fb)->obj,
 					 NULL);
+	mutex_unlock(&dev->struct_mutex);
 	if (ret != 0) {
-		mutex_unlock(&dev->struct_mutex);
 		DRM_ERROR("pin & fence failed\n");
 		return ret;
 	}
@@ -2516,6 +2516,7 @@ intel_pipe_set_base(struct drm_crtc *crtc, int x, int y,
 
 	ret = dev_priv->display.update_plane(crtc, fb, x, y);
 	if (ret) {
+		mutex_lock(&dev->struct_mutex);
 		intel_unpin_fb_obj(to_intel_framebuffer(fb)->obj);
 		mutex_unlock(&dev->struct_mutex);
 		DRM_ERROR("failed to update base address\n");
@@ -2530,9 +2531,12 @@ intel_pipe_set_base(struct drm_crtc *crtc, int x, int y,
 	if (old_fb) {
 		if (intel_crtc->active && old_fb != fb)
 			intel_wait_for_vblank(dev, intel_crtc->pipe);
+		mutex_lock(&dev->struct_mutex);
 		intel_unpin_fb_obj(to_intel_framebuffer(old_fb)->obj);
+		mutex_unlock(&dev->struct_mutex);
 	}
 
+	mutex_lock(&dev->struct_mutex);
 	intel_update_fbc(dev);
 	intel_edp_psr_update(dev);
 	mutex_unlock(&dev->struct_mutex);