[PATCH v4 05/11] drm/fb-helper: Add top-level lock

[Thierry Reding]

From: Thierry Reding <treding at nvidia.com>

Introduce a new top-level lock for the FB helper code. This will allow
better locking granularity and avoid the need to abuse modeset locking
for this purpose instead.

Tested-by: John Stultz <john.stultz at linaro.org>
Reviewed-by: Daniel Vetter <daniel.vetter at ffwll.ch>
Signed-off-by: Thierry Reding <treding at nvidia.com>
---
 drivers/gpu/drm/drm_fb_helper.c | 26 +++++++++++++++++++++++++-
 include/drm/drm_fb_helper.h     | 12 ++++++++++++
 2 files changed, 37 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/drm_fb_helper.c b/drivers/gpu/drm/drm_fb_helper.c
index 18105cbe9810..860be51d92f6 100644
--- a/drivers/gpu/drm/drm_fb_helper.c
+++ b/drivers/gpu/drm/drm_fb_helper.c
@@ -119,6 +119,7 @@ static int __drm_fb_helper_add_one_connector(struct drm_fb_helper *fb_helper,
 	if (!drm_fbdev_emulation)
 		return 0;
 
+	WARN_ON(!mutex_is_locked(&fb_helper->lock));
 	WARN_ON(!mutex_is_locked(&fb_helper->dev->mode_config.mutex));
 
 	count = fb_helper->connector_count + 1;
@@ -150,11 +151,13 @@ int drm_fb_helper_add_one_connector(struct drm_fb_helper *fb_helper,
 {
 	int err;
 
+	mutex_lock(&fb_helper->lock);
 	mutex_lock(&fb_helper->dev->mode_config.mutex);
 
 	err = __drm_fb_helper_add_one_connector(fb_helper, connector);
 
 	mutex_unlock(&fb_helper->dev->mode_config.mutex);
+	mutex_unlock(&fb_helper->lock);
 
 	return err;
 }
@@ -184,6 +187,7 @@ int drm_fb_helper_single_add_all_connectors(struct drm_fb_helper *fb_helper)
 	if (!drm_fbdev_emulation)
 		return 0;
 
+	mutex_lock(&fb_helper->lock);
 	mutex_lock(&dev->mode_config.mutex);
 	drm_connector_list_iter_begin(dev, &conn_iter);
 	drm_for_each_connector_iter(connector, &conn_iter) {
@@ -207,6 +211,7 @@ int drm_fb_helper_single_add_all_connectors(struct drm_fb_helper *fb_helper)
 out:
 	drm_connector_list_iter_end(&conn_iter);
 	mutex_unlock(&dev->mode_config.mutex);
+	mutex_unlock(&fb_helper->lock);
 
 	return ret;
 }
@@ -221,6 +226,7 @@ static int __drm_fb_helper_remove_one_connector(struct drm_fb_helper *fb_helper,
 	if (!drm_fbdev_emulation)
 		return 0;
 
+	WARN_ON(!mutex_is_locked(&fb_helper->lock));
 	WARN_ON(!mutex_is_locked(&fb_helper->dev->mode_config.mutex));
 
 	for (i = 0; i < fb_helper->connector_count; i++) {
@@ -247,11 +253,13 @@ int drm_fb_helper_remove_one_connector(struct drm_fb_helper *fb_helper,
 {
 	int err;
 
+	mutex_lock(&fb_helper->lock);
 	mutex_lock(&fb_helper->dev->mode_config.mutex);
 
 	err = __drm_fb_helper_remove_one_connector(fb_helper, connector);
 
 	mutex_unlock(&fb_helper->dev->mode_config.mutex);
+	mutex_unlock(&fb_helper->lock);
 
 	return err;
 }
@@ -503,16 +511,21 @@ int drm_fb_helper_restore_fbdev_mode_unlocked(struct drm_fb_helper *fb_helper)
 	if (!drm_fbdev_emulation)
 		return -ENODEV;
 
+	mutex_lock(&fb_helper->lock);
 	drm_modeset_lock_all(dev);
+
 	ret = restore_fbdev_mode(fb_helper);
 
 	do_delayed = fb_helper->delayed_hotplug;
 	if (do_delayed)
 		fb_helper->delayed_hotplug = false;
+
 	drm_modeset_unlock_all(dev);
+	mutex_unlock(&fb_helper->lock);
 
 	if (do_delayed)
 		drm_fb_helper_hotplug_event(fb_helper);
+
 	return ret;
 }
 EXPORT_SYMBOL(drm_fb_helper_restore_fbdev_mode_unlocked);
@@ -748,6 +761,7 @@ void drm_fb_helper_prepare(struct drm_device *dev, struct drm_fb_helper *helper,
 	INIT_WORK(&helper->resume_work, drm_fb_helper_resume_worker);
 	INIT_WORK(&helper->dirty_work, drm_fb_helper_dirty_work);
 	helper->dirty_clip.x1 = helper->dirty_clip.y1 = ~0;
+	mutex_init(&helper->lock);
 	helper->funcs = funcs;
 	helper->dev = dev;
 }
@@ -913,6 +927,7 @@ void drm_fb_helper_fini(struct drm_fb_helper *fb_helper)
 	}
 	mutex_unlock(&kernel_fb_helper_lock);
 
+	mutex_destroy(&fb_helper->lock);
 	drm_fb_helper_crtc_free(fb_helper);
 
 }
@@ -2422,25 +2437,34 @@ EXPORT_SYMBOL(drm_fb_helper_initial_config);
 int drm_fb_helper_hotplug_event(struct drm_fb_helper *fb_helper)
 {
 	struct drm_device *dev = fb_helper->dev;
+	int err = 0;
 
 	if (!drm_fbdev_emulation)
 		return 0;
 
+	mutex_lock(&fb_helper->lock);
 	mutex_lock(&dev->mode_config.mutex);
+
 	if (!fb_helper->fb || !drm_fb_helper_is_bound(fb_helper)) {
 		fb_helper->delayed_hotplug = true;
 		mutex_unlock(&dev->mode_config.mutex);
-		return 0;
+		goto unlock;
 	}
+
 	DRM_DEBUG_KMS("\n");
 
 	drm_setup_crtcs(fb_helper, fb_helper->fb->width, fb_helper->fb->height);
 
 	mutex_unlock(&dev->mode_config.mutex);
+	mutex_unlock(&fb_helper->lock);
 
 	drm_fb_helper_set_par(fb_helper->fbdev);
 
 	return 0;
+
+unlock:
+	mutex_unlock(&fb_helper->lock);
+	return err;
 }
 EXPORT_SYMBOL(drm_fb_helper_hotplug_event);
 
diff --git a/include/drm/drm_fb_helper.h b/include/drm/drm_fb_helper.h
index 119e5e4609c7..44e2c57a7049 100644
--- a/include/drm/drm_fb_helper.h
+++ b/include/drm/drm_fb_helper.h
@@ -201,6 +201,18 @@ struct drm_fb_helper {
 	struct work_struct resume_work;
 
 	/**
+	 * @lock:
+	 *
+	 * Top-level FB helper lock. This protects all internal data structures
+	 * and lists, such as @connector_info and @crtc_info.
+	 *
+	 * FIXME: fbdev emulation locking is a mess and long term we want to
+	 * protect all helper internal state with this lock as well as reduce
+	 * core KMS locking as much as possible.
+	 */
+	struct mutex lock;
+
+	/**
 	 * @kernel_fb_list:
 	 *
 	 * Entry on the global kernel_fb_helper_list, used for kgdb entry/exit.
-- 
2.12.0