drm/atomic: Prepare drm_modeset_lock infrastructure for interruptible waiting, v2.

When we want to make drm_atomic_commit interruptible, there are a lot of
places that call the lock function, which we don't have control over.

Rather than trying to convert every single one, it's easier to toggle
interruptible waiting per acquire_ctx. If drm_modeset_acquire_init is
called with DRM_MODESET_ACQUIRE_INTERRUPTIBLE, then we will perform
interruptible waits in drm_modeset_lock and drm_modeset_backoff.

Changes since v1:
- Fix locking example in drm_modeset_lock.c to be compatible
  with interruptible waiting (xexaxo) and make it default.
  Uninterruptible waiting shouldn't happen except in corner cases,
  but the example will still apply if the flag is removed.
- Add drm_modeset_lock_single_interruptible() to documentation.
- Fix dead link to removed drm_modeset_lock_interruptible() in
  drm_modeset_lock().

Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch> #v1
Cc: Emil Velikov <emil.l.velikov@gmail.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20170912133749.6532-2-maarten.lankhorst@linux.intel.com
Reviewed-by: Emil Velikov <emil.l.velikov@gmail.com>

1 files changed, 8 insertions, 4 deletions

diff --git a/include/drm/drm_modeset_lock.h b/include/drm/drm_modeset_lock.h
index 4b27c2bb955c..a685d1bb21f2 100644
--- a/include/drm/drm_modeset_lock.h
+++ b/include/drm/drm_modeset_lock.h
@@ -34,6 +34,7 @@ struct drm_modeset_lock;
  * @contended: used internally for -EDEADLK handling
  * @locked: list of held locks
  * @trylock_only: trylock mode used in atomic contexts/panic notifiers
+ * @interruptible: whether interruptible locking should be used.
  *
  * Each thread competing for a set of locks must use one acquire
  * ctx.  And if any lock fxn returns -EDEADLK, it must backoff and
@@ -59,6 +60,9 @@ struct drm_modeset_acquire_ctx {
 	 * Trylock mode, use only for panic handlers!
 	 */
 	bool trylock_only;
+
+	/* Perform interruptible waits on this context. */
+	bool interruptible;
 };
 
 /**
@@ -82,12 +86,13 @@ struct drm_modeset_lock {
 	struct list_head head;
 };
 
+#define DRM_MODESET_ACQUIRE_INTERRUPTIBLE BIT(0)
+
 void drm_modeset_acquire_init(struct drm_modeset_acquire_ctx *ctx,
 		uint32_t flags);
 void drm_modeset_acquire_fini(struct drm_modeset_acquire_ctx *ctx);
 void drm_modeset_drop_locks(struct drm_modeset_acquire_ctx *ctx);
-void drm_modeset_backoff(struct drm_modeset_acquire_ctx *ctx);
-int drm_modeset_backoff_interruptible(struct drm_modeset_acquire_ctx *ctx);
+int drm_modeset_backoff(struct drm_modeset_acquire_ctx *ctx);
 
 void drm_modeset_lock_init(struct drm_modeset_lock *lock);
 
@@ -111,8 +116,7 @@ static inline bool drm_modeset_is_locked(struct drm_modeset_lock *lock)
 
 int drm_modeset_lock(struct drm_modeset_lock *lock,
 		struct drm_modeset_acquire_ctx *ctx);
-int drm_modeset_lock_interruptible(struct drm_modeset_lock *lock,
-		struct drm_modeset_acquire_ctx *ctx);
+int __must_check drm_modeset_lock_single_interruptible(struct drm_modeset_lock *lock);
 void drm_modeset_unlock(struct drm_modeset_lock *lock);
 
 struct drm_device;