[PATCH v2 03/11] drm/fb-helper: Ensure driver module is pinned in fb_open()

[Noralf Trønnes]

If struct fb_ops is defined in a library like cma, fb_open() takes a
ref on the library instead of the driver module. Use
fb_ops.fb_open/fb_release to ensure that the driver module is pinned.

Add drm_fb_helper_fb_open() and drm_fb_helper_fb_release() to
DRM_FB_HELPER_DEFAULT_OPS().

Signed-off-by: Noralf Trønnes <noralf at tronnes.org>
---
 drivers/gpu/drm/drm_fb_helper.c | 41 +++++++++++++++++++++++++++++++++++++++++
 include/drm/drm_fb_helper.h     | 14 ++++++++++++++
 2 files changed, 55 insertions(+)

diff --git a/drivers/gpu/drm/drm_fb_helper.c b/drivers/gpu/drm/drm_fb_helper.c
index 74c1053..b080004 100644
--- a/drivers/gpu/drm/drm_fb_helper.c
+++ b/drivers/gpu/drm/drm_fb_helper.c
@@ -1037,6 +1037,47 @@ void drm_fb_helper_fb_destroy(struct fb_info *info)
 EXPORT_SYMBOL(drm_fb_helper_fb_destroy);
 
 /**
+ * drm_fb_helper_fb_open - implementation for &fb_ops.fb_open
+ * @info: fbdev registered by the helper
+ * @user: 1=userspace, 0=fbcon
+ *
+ * If &fb_ops is wrapped in a library, pin the driver module.
+ */
+int drm_fb_helper_fb_open(struct fb_info *info, int user)
+{
+	struct drm_fb_helper *fb_helper = info->par;
+	struct drm_device *dev = fb_helper->dev;
+
+	/* Skip fbcon, it detaches itself in unregister_framebuffer() */
+	if (user && info->fbops->owner != dev->driver->fops->owner) {
+		if (!try_module_get(dev->driver->fops->owner))
+			return -ENODEV;
+	}
+
+	return 0;
+}
+EXPORT_SYMBOL(drm_fb_helper_fb_open);
+
+/**
+ * drm_fb_helper_fb_release - implementation for &fb_ops.fb_release
+ * @info: fbdev registered by the helper
+ * @user: 1=userspace, 0=fbcon
+ *
+ * If &fb_ops is wrapped in a library, unpin the driver module.
+ */
+int drm_fb_helper_fb_release(struct fb_info *info, int user)
+{
+	struct drm_fb_helper *fb_helper = info->par;
+	struct drm_device *dev = fb_helper->dev;
+
+	if (user && info->fbops->owner != dev->driver->fops->owner)
+		module_put(dev->driver->fops->owner);
+
+	return 0;
+}
+EXPORT_SYMBOL(drm_fb_helper_fb_release);
+
+/**
  * drm_fb_helper_sys_read - wrapper around fb_sys_read
  * @info: fb_info struct pointer
  * @buf: userspace buffer to read from framebuffer memory
diff --git a/include/drm/drm_fb_helper.h b/include/drm/drm_fb_helper.h
index dd78eb3..b44fc62 100644
--- a/include/drm/drm_fb_helper.h
+++ b/include/drm/drm_fb_helper.h
@@ -233,6 +233,8 @@ struct drm_fb_helper {
  */
 #define DRM_FB_HELPER_DEFAULT_OPS \
 	.fb_destroy	= drm_fb_helper_fb_destroy, \
+	.fb_open	= drm_fb_helper_fb_open, \
+	.fb_release	= drm_fb_helper_fb_release, \
 	.fb_check_var	= drm_fb_helper_check_var, \
 	.fb_set_par	= drm_fb_helper_set_par, \
 	.fb_setcmap	= drm_fb_helper_setcmap, \
@@ -270,6 +272,8 @@ void drm_fb_helper_deferred_io(struct fb_info *info,
 			       struct list_head *pagelist);
 
 void drm_fb_helper_fb_destroy(struct fb_info *info);
+int drm_fb_helper_fb_open(struct fb_info *info, int user);
+int drm_fb_helper_fb_release(struct fb_info *info, int user);
 
 ssize_t drm_fb_helper_sys_read(struct fb_info *info, char __user *buf,
 			       size_t count, loff_t *ppos);
@@ -405,6 +409,16 @@ static inline void drm_fb_helper_fb_destroy(struct fb_info *info)
 {
 }
 
+static inline int drm_fb_helper_fb_open(struct fb_info *info, int user)
+{
+	return -ENODEV;
+}
+
+static inline int drm_fb_helper_fb_release(struct fb_info *info, int user)
+{
+	return -ENODEV;
+}
+
 static inline ssize_t drm_fb_helper_sys_read(struct fb_info *info,
 					     char __user *buf, size_t count,
 					     loff_t *ppos)
-- 
2.7.4