drm: refcounting for crtc framebuffers

With the prep patch to encapsulate ->set_crtc calls, this is now
rather easy. Hooray for inconsistent semantics between ->set_crtc and
->page_flip, where the driver callback is supposed to update the fb
pointer, and ->update_plane, where the drm core does the same.

Also, since the drm core functions check crtc->fb before calling into
driver callbacks, we can't really reduce the critical sections
protected by the mode_config locks.

Reviewed-by: Rob Clark <rob@ti.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

1 files changed, 30 insertions, 7 deletions

diff --git a/drivers/gpu/drm/drm_crtc.c b/drivers/gpu/drm/drm_crtc.c
index 64ef12079528..6dc75ee10079 100644
--- a/drivers/gpu/drm/drm_crtc.c
+++ b/drivers/gpu/drm/drm_crtc.c
@@ -1984,8 +1984,21 @@ out:
 int drm_mode_set_config_internal(struct drm_mode_set *set)
 {
         struct drm_crtc *crtc = set->crtc;
+        struct drm_framebuffer *fb, *old_fb;
+        int ret;
+
+        old_fb = crtc->fb;
+        fb = set->fb;
 
-        return crtc->funcs->set_config(set);
+        ret = crtc->funcs->set_config(set);
+        if (ret == 0) {
+                if (old_fb)
+                        drm_framebuffer_unreference(old_fb);
+                if (fb)
+                        drm_framebuffer_reference(fb);
+        }
+
+        return ret;
 }
 EXPORT_SYMBOL(drm_mode_set_config_internal);
 
@@ -2046,6 +2059,8 @@ int drm_mode_setcrtc(struct drm_device *dev, void *data,
                                 goto out;
                         }
                         fb = crtc->fb;
+                        /* Make refcounting symmetric with the lookup path. */
+                        drm_framebuffer_reference(fb);
                 } else {
                         fb = drm_framebuffer_lookup(dev, crtc_req->fb_id);
                         if (!fb) {
@@ -2054,9 +2069,6 @@ int drm_mode_setcrtc(struct drm_device *dev, void *data,
                                 ret = -EINVAL;
                                 goto out;
                         }
-                        /* fb is protect by the mode_config lock, so drop the
-                         * ref immediately */
-                        drm_framebuffer_unreference(fb);
                 }
 
                 mode = drm_mode_create(dev);
@@ -2156,6 +2168,9 @@ int drm_mode_setcrtc(struct drm_device *dev, void *data,
         ret = drm_mode_set_config_internal(&set);
 
 out:
+        if (fb)
+                drm_framebuffer_unreference(fb);
+
         kfree(connector_set);
         drm_mode_destroy(dev, mode);
         drm_modeset_unlock_all(dev);
@@ -3656,7 +3671,7 @@ int drm_mode_page_flip_ioctl(struct drm_device *dev,
         struct drm_mode_crtc_page_flip *page_flip = data;
         struct drm_mode_object *obj;
         struct drm_crtc *crtc;
-        struct drm_framebuffer *fb;
+        struct drm_framebuffer *fb = NULL, *old_fb = NULL;
         struct drm_pending_vblank_event *e = NULL;
         unsigned long flags;
         int hdisplay, vdisplay;
@@ -3687,8 +3702,6 @@ int drm_mode_page_flip_ioctl(struct drm_device *dev,
         fb = drm_framebuffer_lookup(dev, page_flip->fb_id);
         if (!fb)
                 goto out;
-        /* fb is protect by the mode_config lock, so drop the ref immediately */
-        drm_framebuffer_unreference(fb);
 
         hdisplay = crtc->mode.hdisplay;
         vdisplay = crtc->mode.vdisplay;
@@ -3734,6 +3747,7 @@ int drm_mode_page_flip_ioctl(struct drm_device *dev,
                         (void (*) (struct drm_pending_event *)) kfree;
         }
 
+        old_fb = crtc->fb;
         ret = crtc->funcs->page_flip(crtc, fb, e);
         if (ret) {
                 if (page_flip->flags & DRM_MODE_PAGE_FLIP_EVENT) {
@@ -3742,9 +3756,18 @@ int drm_mode_page_flip_ioctl(struct drm_device *dev,
                         spin_unlock_irqrestore(&dev->event_lock, flags);
                         kfree(e);
                 }
+                /* Keep the old fb, don't unref it. */
+                old_fb = NULL;
+        } else {
+                /* Unref only the old framebuffer. */
+                fb = NULL;
         }
 
 out:
+        if (fb)
+                drm_framebuffer_unreference(fb);
+        if (old_fb)
+                drm_framebuffer_unreference(old_fb);
         drm_modeset_unlock_all(dev);
         return ret;
 }