drm/fb-helper: Fix locking in drm_fb_helper_hotplug_event

Driver's and ->fill_modes functions are allowed to grab crtc mutexes
(for e.g. load detect). Hence we need to first only grab the general
kms mutex, and only in a second step grab all locks to do the
modesets.

This prevents a deadlock on my gm45 in the tv load detect code called
by drm_helper_probe_single_connector_modes.

Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Dave Airlie <airlied@redhat.com>

diff --git a/drivers/gpu/drm/drm_fb_helper.c b/drivers/gpu/drm/drm_fb_helper.c
index 59d6b9b..892ff9f 100644 (file)
--- a/drivers/gpu/drm/drm_fb_helper.c
+++ b/drivers/gpu/drm/drm_fb_helper.c
@@ -1544,10 +1544,10 @@ int drm_fb_helper_hotplug_event(struct drm_fb_helper *fb_helper)
        if (!fb_helper->fb)
                return 0;
 
-       drm_modeset_lock_all(dev);
+       mutex_lock(&fb_helper->dev->mode_config.mutex);
        if (!drm_fb_helper_is_bound(fb_helper)) {
                fb_helper->delayed_hotplug = true;
-               drm_modeset_unlock_all(dev);
+               mutex_unlock(&fb_helper->dev->mode_config.mutex);
                return 0;
        }
        DRM_DEBUG_KMS("\n");
@@ -1558,9 +1558,11 @@ int drm_fb_helper_hotplug_event(struct drm_fb_helper *fb_helper)
 
        count = drm_fb_helper_probe_connector_modes(fb_helper, max_width,
                                                    max_height);
+       mutex_unlock(&fb_helper->dev->mode_config.mutex);
+
+       drm_modeset_lock_all(dev);
        drm_setup_crtcs(fb_helper);
        drm_modeset_unlock_all(dev);
-
        drm_fb_helper_set_par(fb_helper->fbdev);
 
        return 0;