drm: Add DRM_MODESET_LOCK_BEGIN/END helpers

This patch adds a couple of helpers to remove the boilerplate involved
in grabbing all of the modeset locks.

I've also converted the obvious cases in drm core to use the helpers.

The only remaining instance of drm_modeset_lock_all_ctx() is in
drm_framebuffer. It's complicated by the state clear that occurs on
deadlock. ATM, there's no way to inject code in the deadlock path with
the helpers, so it's unfit for conversion.

Changes in v2:
- Relocate ret argument to the end of the list (Daniel)
- Incorporate Daniel's doc suggestions (Daniel)

Suggested-by: Daniel Vetter <daniel@ffwll.ch>
Reviewed-by: Daniel Vetter <daniel@ffwll.ch>
Signed-off-by: Sean Paul <seanpaul@chromium.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20181129150423.239081-4-sean@poorly.run

1 files changed, 6 insertions, 0 deletions

diff --git a/drivers/gpu/drm/drm_modeset_lock.c b/drivers/gpu/drm/drm_modeset_lock.c
index 8a5100685875..51f534db9107 100644
--- a/drivers/gpu/drm/drm_modeset_lock.c
+++ b/drivers/gpu/drm/drm_modeset_lock.c
@@ -56,6 +56,10 @@
  *     drm_modeset_drop_locks(ctx);
  *     drm_modeset_acquire_fini(ctx);
  *
+ * For convenience this control flow is implemented in
+ * DRM_MODESET_LOCK_ALL_BEGIN() and DRM_MODESET_LOCK_ALL_END() for the case
+ * where all modeset locks need to be taken through drm_modeset_lock_all_ctx().
+ *
  * If all that is needed is a single modeset lock, then the &struct
  * drm_modeset_acquire_ctx is not needed and the locking can be simplified
  * by passing a NULL instead of ctx in the drm_modeset_lock() call or
@@ -383,6 +387,8 @@ EXPORT_SYMBOL(drm_modeset_unlock);
  * Locks acquired with this function should be released by calling the
  * drm_modeset_drop_locks() function on @ctx.
  *
+ * See also: DRM_MODESET_LOCK_ALL_BEGIN() and DRM_MODESET_LOCK_ALL_END()
+ *
  * Returns: 0 on success or a negative error-code on failure.
  */
 int drm_modeset_lock_all_ctx(struct drm_device *dev,