Revert "drm: cleanup: remove drm_modeset_(un)lock_all()"

This reverts commit 8d813d1a53.

This patchset breaks on intel platforms and was previously NACK'd by
Ville.

Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Cc: Fernando Ramos <greenfoo@u92.eu>
Acked-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Sean Paul <seanpaul@chromium.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20211002154542.15800-1-sean@poorly.run

drivers/gpu/drm/drm_modeset_lock.c

@@ -77,6 +77,93 @@
 
 static DEFINE_WW_CLASS(crtc_ww_class);
 
+/**
+ * drm_modeset_lock_all - take all modeset locks
+ * @dev: DRM device
+ *
+ * This function takes all modeset locks, suitable where a more fine-grained
+ * scheme isn't (yet) implemented. Locks must be dropped by calling the
+ * drm_modeset_unlock_all() function.
+ *
+ * This function is deprecated. It allocates a lock acquisition context and
+ * stores it in &drm_device.mode_config. This facilitate conversion of
+ * existing code because it removes the need to manually deal with the
+ * acquisition context, but it is also brittle because the context is global
+ * and care must be taken not to nest calls. New code should use the
+ * drm_modeset_lock_all_ctx() function and pass in the context explicitly.
+ */
+void drm_modeset_lock_all(struct drm_device *dev)
+{
+	struct drm_mode_config *config = &dev->mode_config;
+	struct drm_modeset_acquire_ctx *ctx;
+	int ret;
+
+	ctx = kzalloc(sizeof(*ctx), GFP_KERNEL | __GFP_NOFAIL);
+	if (WARN_ON(!ctx))
+		return;
+
+	mutex_lock(&config->mutex);
+
+	drm_modeset_acquire_init(ctx, 0);
+
+retry:
+	ret = drm_modeset_lock_all_ctx(dev, ctx);
+	if (ret < 0) {
+		if (ret == -EDEADLK) {
+			drm_modeset_backoff(ctx);
+			goto retry;
+		}
+
+		drm_modeset_acquire_fini(ctx);
+		kfree(ctx);
+		return;
+	}
+	ww_acquire_done(&ctx->ww_ctx);
+
+	WARN_ON(config->acquire_ctx);
+
+	/*
+	 * We hold the locks now, so it is safe to stash the acquisition
+	 * context for drm_modeset_unlock_all().
+	 */
+	config->acquire_ctx = ctx;
+
+	drm_warn_on_modeset_not_all_locked(dev);
+}
+EXPORT_SYMBOL(drm_modeset_lock_all);
+
+/**
+ * drm_modeset_unlock_all - drop all modeset locks
+ * @dev: DRM device
+ *
+ * This function drops all modeset locks taken by a previous call to the
+ * drm_modeset_lock_all() function.
+ *
+ * This function is deprecated. It uses the lock acquisition context stored
+ * in &drm_device.mode_config. This facilitates conversion of existing
+ * code because it removes the need to manually deal with the acquisition
+ * context, but it is also brittle because the context is global and care must
+ * be taken not to nest calls. New code should pass the acquisition context
+ * directly to the drm_modeset_drop_locks() function.
+ */
+void drm_modeset_unlock_all(struct drm_device *dev)
+{
+	struct drm_mode_config *config = &dev->mode_config;
+	struct drm_modeset_acquire_ctx *ctx = config->acquire_ctx;
+
+	if (WARN_ON(!ctx))
+		return;
+
+	config->acquire_ctx = NULL;
+	drm_modeset_drop_locks(ctx);
+	drm_modeset_acquire_fini(ctx);
+
+	kfree(ctx);
+
+	mutex_unlock(&dev->mode_config.mutex);
+}
+EXPORT_SYMBOL(drm_modeset_unlock_all);
+
 /**
  * drm_warn_on_modeset_not_all_locked - check that all modeset locks are locked
  * @dev: device
@@ -293,9 +380,10 @@ EXPORT_SYMBOL(drm_modeset_unlock);
  * This function takes all modeset locks, suitable where a more fine-grained
  * scheme isn't (yet) implemented.
  *
- * It doesn't take the &drm_mode_config.mutex since that lock isn't required for
- * modeset state changes. Callers which need to grab that lock too need to do so
- * outside of the acquire context @ctx.
+ * Unlike drm_modeset_lock_all(), it doesn't take the &drm_mode_config.mutex
+ * since that lock isn't required for modeset state changes. Callers which
+ * need to grab that lock too need to do so outside of the acquire context
+ * @ctx.
  *
  * Locks acquired with this function should be released by calling the
  * drm_modeset_drop_locks() function on @ctx.

include/drm/drm_modeset_lock.h

@@ -132,6 +132,8 @@ struct drm_device;
 struct drm_crtc;
 struct drm_plane;
 
+void drm_modeset_lock_all(struct drm_device *dev);
+void drm_modeset_unlock_all(struct drm_device *dev);
 void drm_warn_on_modeset_not_all_locked(struct drm_device *dev);
 
 int drm_modeset_lock_all_ctx(struct drm_device *dev,