drm/atomic: Acquire connection_mutex lock in drm_helper_probe_single_connector_modes, v4.

mode_valid() called from drm_helper_probe_single_connector_modes()
may need to look at connector->state because what a valid mode is may
depend on connector properties being set. For example some HDMI modes
might be rejected when a connector property forces the connector
into DVI mode.

Some implementations of detect() already lock all state,
so we have to pass an acquire_ctx to them to prevent a deadlock.

This means changing the function signature of detect() slightly,
and passing the acquire_ctx for locking multiple crtc's.
For the callbacks, it will always be non-zero. To allow callers
not to worry about this, drm_helper_probe_detect_ctx is added
which might handle -EDEADLK for you.

Changes since v1:
- Always set ctx parameter.
Changes since v2:
- Always take connection_mutex when probing.
Changes since v3:
- Remove the ctx from intel_dp_long_pulse, and add
  WARN_ON(!connection_mutex) (danvet)
- Update docs to clarify the locking situation. (danvet)

Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Cc: Boris Brezillon <boris.brezillon@free-electrons.com>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/1491504920-4017-1-git-send-email-maarten.lankhorst@linux.intel.com

1 files changed, 6 insertions, 0 deletions

diff --git a/include/drm/drm_connector.h b/include/drm/drm_connector.h
index 941f57f311aa..e2ee74c20b8f 100644
--- a/include/drm/drm_connector.h
+++ b/include/drm/drm_connector.h
@@ -32,6 +32,7 @@
 struct drm_device;
 
 struct drm_connector_helper_funcs;
+struct drm_modeset_acquire_ctx;
 struct drm_device;
 struct drm_crtc;
 struct drm_encoder;
@@ -378,6 +379,11 @@ struct drm_connector_funcs {
 	 * the helper library vtable purely for historical reasons. The only DRM
 	 * core	entry point to probe connector state is @fill_modes.
 	 *
+	 * Note that the helper library will already hold
+	 * &drm_mode_config.connection_mutex. Drivers which need to grab additional
+	 * locks to avoid races with concurrent modeset changes need to use
+	 * &drm_connector_helper_funcs.detect_ctx instead.
+	 *
 	 * RETURNS:
 	 *
 	 * drm_connector_status indicating the connector's status.