[PATCH 1/4] drm: Introduce drm_modeset_lock_ctx_retry()

[Ville Syrjala]

From: Ville Syrjälä <ville.syrjala at linux.intel.com>

Quite a few places are hand rolling the modeset lock backoff dance.
Let's suck that into a helper macro that is easier to use without
forgetting some steps.

The main downside is probably that the implementation of
drm_with_modeset_lock_ctx() is a bit harder to read than a hand
rolled version on account of being split across three functions,
but the actual code using it ends up being much simpler.

Cc: Sean Paul <seanpaul at chromium.org>
Cc: Daniel Vetter <daniel at ffwll.ch>
Signed-off-by: Ville Syrjälä <ville.syrjala at linux.intel.com>
---
 drivers/gpu/drm/drm_modeset_lock.c | 44 ++++++++++++++++++++++++++++++
 include/drm/drm_modeset_lock.h     | 20 ++++++++++++++
 2 files changed, 64 insertions(+)

diff --git a/drivers/gpu/drm/drm_modeset_lock.c b/drivers/gpu/drm/drm_modeset_lock.c
index fcfe1a03c4a1..083df96632e8 100644
--- a/drivers/gpu/drm/drm_modeset_lock.c
+++ b/drivers/gpu/drm/drm_modeset_lock.c
@@ -425,3 +425,47 @@ int drm_modeset_lock_all_ctx(struct drm_device *dev,
 	return 0;
 }
 EXPORT_SYMBOL(drm_modeset_lock_all_ctx);
+
+void _drm_modeset_lock_begin(struct drm_modeset_acquire_ctx *ctx,
+			     struct drm_atomic_state *state,
+			     unsigned int flags, int *ret)
+{
+	drm_modeset_acquire_init(ctx, flags);
+
+	if (state)
+		state->acquire_ctx = ctx;
+
+	*ret = -EDEADLK;
+}
+EXPORT_SYMBOL(_drm_modeset_lock_begin);
+
+bool _drm_modeset_lock_loop(int *ret)
+{
+	if (*ret == -EDEADLK) {
+		*ret = 0;
+		return true;
+	}
+
+	return false;
+}
+EXPORT_SYMBOL(_drm_modeset_lock_loop);
+
+void _drm_modeset_lock_end(struct drm_modeset_acquire_ctx *ctx,
+			   struct drm_atomic_state *state,
+			   int *ret)
+{
+	if (*ret == -EDEADLK) {
+		if (state)
+			drm_atomic_state_clear(state);
+
+		*ret = drm_modeset_backoff(ctx);
+		if (*ret == 0) {
+			*ret = -EDEADLK;
+			return;
+		}
+	}
+
+	drm_modeset_drop_locks(ctx);
+	drm_modeset_acquire_fini(ctx);
+}
+EXPORT_SYMBOL(_drm_modeset_lock_end);
diff --git a/include/drm/drm_modeset_lock.h b/include/drm/drm_modeset_lock.h
index aafd07388eb7..5eaad2533de5 100644
--- a/include/drm/drm_modeset_lock.h
+++ b/include/drm/drm_modeset_lock.h
@@ -26,6 +26,7 @@
 
 #include <linux/ww_mutex.h>
 
+struct drm_atomic_state;
 struct drm_modeset_lock;
 
 /**
@@ -203,4 +204,23 @@ modeset_lock_fail:							\
 	if (!drm_drv_uses_atomic_modeset(dev))				\
 		mutex_unlock(&dev->mode_config.mutex);
 
+void _drm_modeset_lock_begin(struct drm_modeset_acquire_ctx *ctx,
+			     struct drm_atomic_state *state,
+			     unsigned int flags,
+			     int *ret);
+bool _drm_modeset_lock_loop(int *ret);
+void _drm_modeset_lock_end(struct drm_modeset_acquire_ctx *ctx,
+			   struct drm_atomic_state *state,
+			   int *ret);
+
+/*
+ * Note that one must always use "continue" rather than
+ * "break" or "return" to handle errors within the
+ * drm_modeset_lock_ctx_retry() block.
+ */
+#define drm_modeset_lock_ctx_retry(ctx, state, flags, ret) \
+	for (_drm_modeset_lock_begin((ctx), (state), (flags), &(ret)); \
+	     _drm_modeset_lock_loop(&(ret)); \
+	     _drm_modeset_lock_end((ctx), (state), &(ret)))
+
 #endif /* DRM_MODESET_LOCK_H_ */
-- 
2.31.1