drm/fb-helper: Don't clobber the display palette when fbdev isn't bound

Perform the drm_fb_helper_is_bound() check to avoid clobbering the
display palette of some other KMS client.

While at it, fix up the locking by grabbing all modeset locks for the
duration of the fb_setcmap operation.

v2: Make a note of the locking changes in the commit message
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Dave Airlie <airlied@gmail.com>

drivers/gpu/drm/drm_fb_helper.c

@@ -640,12 +640,19 @@ static int setcolreg(struct drm_crtc *crtc, u16 red, u16 green,
 int drm_fb_helper_setcmap(struct fb_cmap *cmap, struct fb_info *info)
 {
 	struct drm_fb_helper *fb_helper = info->par;
+	struct drm_device *dev = fb_helper->dev;
 	struct drm_crtc_helper_funcs *crtc_funcs;
 	u16 *red, *green, *blue, *transp;
 	struct drm_crtc *crtc;
 	int i, j, rc = 0;
 	int start;
 
+	drm_modeset_lock_all(dev);
+	if (!drm_fb_helper_is_bound(fb_helper)) {
+		drm_modeset_unlock_all(dev);
+		return -EBUSY;
+	}
+
 	for (i = 0; i < fb_helper->crtc_count; i++) {
 		crtc = fb_helper->crtc_info[i].mode_set.crtc;
 		crtc_funcs = crtc->helper_private;
@@ -668,10 +675,12 @@ int drm_fb_helper_setcmap(struct fb_cmap *cmap, struct fb_info *info)
 
 			rc = setcolreg(crtc, hred, hgreen, hblue, start++, info);
 			if (rc)
-				return rc;
+				goto out;
 		}
 		crtc_funcs->load_lut(crtc);
 	}
+ out:
+	drm_modeset_unlock_all(dev);
 	return rc;
 }
 EXPORT_SYMBOL(drm_fb_helper_setcmap);