fbcon: Extract fbcon_open/release helpers

There's two minor behaviour changes in here:
- in error paths we now consistently call fb_ops->fb_release
- fb_release really can't fail (fbmem.c ignores it too) and there's no
  reasonable cleanup we can do anyway.

Note that everything in fbcon.c is protected by the big console_lock()
lock (especially all the global variables), so the minor changes in
ordering of setup/cleanup do not matter.

v2: Explain a bit better why this is all correct (Sam)

Acked-by: Sam Ravnborg <sam@ravnborg.org>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Cc: Daniel Vetter <daniel@ffwll.ch>
Cc: Claudio Suarez <cssk@net-c.es>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Cc: Du Cheng <ducheng2@gmail.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220405210335.3434130-10-daniel.vetter@ffwll.ch

drivers/video/fbdev/core/fbcon.c

@@ -682,19 +682,37 @@ static int fbcon_invalid_charcount(struct fb_info *info, unsigned charcount)
 
 #endif /* CONFIG_MISC_TILEBLITTING */
 
+static int fbcon_open(struct fb_info *info)
+{
+	if (!try_module_get(info->fbops->owner))
+		return -ENODEV;
+
+	if (info->fbops->fb_open &&
+	    info->fbops->fb_open(info, 0)) {
+		module_put(info->fbops->owner);
+		return -ENODEV;
+	}
+
+	return 0;
+}
+
+static void fbcon_release(struct fb_info *info)
+{
+	if (info->fbops->fb_release)
+		info->fbops->fb_release(info, 0);
+
+	module_put(info->fbops->owner);
+}
 
 static int con2fb_acquire_newinfo(struct vc_data *vc, struct fb_info *info,
 				  int unit, int oldidx)
 {
 	struct fbcon_ops *ops = NULL;
-	int err = 0;
+	int err;
 
-	if (!try_module_get(info->fbops->owner))
-		err = -ENODEV;
-
-	if (!err && info->fbops->fb_open &&
-	    info->fbops->fb_open(info, 0))
-		err = -ENODEV;
+	err = fbcon_open(info);
+	if (err)
+		return err;
 
 	if (!err) {
 		ops = kzalloc(sizeof(struct fbcon_ops), GFP_KERNEL);
@@ -715,7 +733,7 @@ static int con2fb_acquire_newinfo(struct vc_data *vc, struct fb_info *info,
 
 	if (err) {
 		con2fb_map[unit] = oldidx;
-		module_put(info->fbops->owner);
+		fbcon_release(info);
 	}
 
 	return err;
@@ -726,45 +744,34 @@ static int con2fb_release_oldinfo(struct vc_data *vc, struct fb_info *oldinfo,
 				  int oldidx, int found)
 {
 	struct fbcon_ops *ops = oldinfo->fbcon_par;
-	int err = 0, ret;
+	int ret;
 
-	if (oldinfo->fbops->fb_release &&
-	    oldinfo->fbops->fb_release(oldinfo, 0)) {
-		con2fb_map[unit] = oldidx;
-		if (!found && newinfo->fbops->fb_release)
-			newinfo->fbops->fb_release(newinfo, 0);
-		if (!found)
-			module_put(newinfo->fbops->owner);
-		err = -ENODEV;
+	fbcon_release(oldinfo);
+
+	fbcon_del_cursor_work(oldinfo);
+	kfree(ops->cursor_state.mask);
+	kfree(ops->cursor_data);
+	kfree(ops->cursor_src);
+	kfree(ops->fontbuffer);
+	kfree(oldinfo->fbcon_par);
+	oldinfo->fbcon_par = NULL;
+	/*
+	  If oldinfo and newinfo are driving the same hardware,
+	  the fb_release() method of oldinfo may attempt to
+	  restore the hardware state.  This will leave the
+	  newinfo in an undefined state. Thus, a call to
+	  fb_set_par() may be needed for the newinfo.
+	*/
+	if (newinfo && newinfo->fbops->fb_set_par) {
+		ret = newinfo->fbops->fb_set_par(newinfo);
+
+		if (ret)
+			printk(KERN_ERR "con2fb_release_oldinfo: "
+				"detected unhandled fb_set_par error, "
+				"error code %d\n", ret);
 	}
 
-	if (!err) {
-		fbcon_del_cursor_work(oldinfo);
-		kfree(ops->cursor_state.mask);
-		kfree(ops->cursor_data);
-		kfree(ops->cursor_src);
-		kfree(ops->fontbuffer);
-		kfree(oldinfo->fbcon_par);
-		oldinfo->fbcon_par = NULL;
-		module_put(oldinfo->fbops->owner);
-		/*
-		  If oldinfo and newinfo are driving the same hardware,
-		  the fb_release() method of oldinfo may attempt to
-		  restore the hardware state.  This will leave the
-		  newinfo in an undefined state. Thus, a call to
-		  fb_set_par() may be needed for the newinfo.
-		*/
-		if (newinfo && newinfo->fbops->fb_set_par) {
-			ret = newinfo->fbops->fb_set_par(newinfo);
-
-			if (ret)
-				printk(KERN_ERR "con2fb_release_oldinfo: "
-					"detected unhandled fb_set_par error, "
-					"error code %d\n", ret);
-		}
-	}
-
-	return err;
+	return 0;
 }
 
 static void con2fb_init_display(struct vc_data *vc, struct fb_info *info,
@@ -919,7 +926,6 @@ static const char *fbcon_startup(void)
 	struct fbcon_display *p = &fb_display[fg_console];
 	struct vc_data *vc = vc_cons[fg_console].d;
 	const struct font_desc *font = NULL;
-	struct module *owner;
 	struct fb_info *info = NULL;
 	struct fbcon_ops *ops;
 	int rows, cols;
@@ -938,17 +944,12 @@ static const char *fbcon_startup(void)
 	if (!info)
 		return NULL;
 	
-	owner = info->fbops->owner;
-	if (!try_module_get(owner))
+	if (fbcon_open(info))
 		return NULL;
-	if (info->fbops->fb_open && info->fbops->fb_open(info, 0)) {
-		module_put(owner);
-		return NULL;
-	}
 
 	ops = kzalloc(sizeof(struct fbcon_ops), GFP_KERNEL);
 	if (!ops) {
-		module_put(owner);
+		fbcon_release(info);
 		return NULL;
 	}
 
@@ -3314,10 +3315,6 @@ static void fbcon_exit(void)
 		}
 
 		if (mapped) {
-			if (info->fbops->fb_release)
-				info->fbops->fb_release(info, 0);
-			module_put(info->fbops->owner);
-
 			if (info->fbcon_par) {
 				struct fbcon_ops *ops = info->fbcon_par;
 
@@ -3327,6 +3324,8 @@ static void fbcon_exit(void)
 				kfree(info->fbcon_par);
 				info->fbcon_par = NULL;
 			}
+
+			fbcon_release(info);
 		}
 	}
 }