Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
From:   Felipe Balbi <felipe.balbi@linux.intel.com>
To:     Chunfeng Yun <chunfeng.yun@mediatek.com>
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Matthias Brugger <matthias.bgg@gmail.com>,
        Randy Dunlap <rdunlap@infradead.org>,
        linux-usb@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
        linux-mediatek@lists.infradead.org, linux-kernel@vger.kernel.org
Subject: Re: [v3 PATCH] usb: create usb_debug_root for gadget only
In-Reply-To: <1559201499.8487.40.camel@mhfsdcap03>
References: <cffd6d75f69e4d908c8f39b8a60ddae27d6b7c88.1559028752.git.chunfeng.yun@mediatek.com> <87k1ebj8vt.fsf@linux.intel.com> <1559201499.8487.40.camel@mhfsdcap03>
Date:   Fri, 31 May 2019 08:44:55 +0300
Message-ID: <87sgsv2n54.fsf@linux.intel.com>
MIME-Version: 1.0
Content-Type: text/plain
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk


Hi,

Chunfeng Yun <chunfeng.yun@mediatek.com> writes:

> Hi Felipe,
> On Tue, 2019-05-28 at 11:11 +0300, Felipe Balbi wrote:
>> Hi,
>> 
>> Chunfeng Yun <chunfeng.yun@mediatek.com> writes:
>> > diff --git a/drivers/usb/core/usb.c b/drivers/usb/core/usb.c
>> > index 7fcb9f782931..88b3ee03a12d 100644
>> > --- a/drivers/usb/core/usb.c
>> > +++ b/drivers/usb/core/usb.c
>> > @@ -1190,7 +1190,7 @@ EXPORT_SYMBOL_GPL(usb_debug_root);
>> >  
>> >  static void usb_debugfs_init(void)
>> >  {
>> > -	usb_debug_root = debugfs_create_dir("usb", NULL);
>> > +	usb_debug_root = debugfs_create_dir(USB_DEBUG_ROOT_NAME, NULL);
>> >  	debugfs_create_file("devices", 0444, usb_debug_root, NULL,
>> >  			    &usbfs_devices_fops);
>> >  }
>> 
>> might be a better idea to move this to usb common. Then have a function
>> which can be called by both host and gadget to maybe create the
>> directory:
>> 
>> static struct dentry *usb_debug_root;
>> 
>> struct dentry *usb_debugfs_init(void)
>> {
>> 	if (!usb_debug_root)
>>         	usb_debug_root = debugfs_create_dir("usb", NULL);
>> 
>> 	return usb_debug_root;
>> }
>> 
>> 
>> Then usb core would be updated to something like:
>> 
>> static void usb_core_debugfs_init(void)
>> {
>> 	struct dentry *root = usb_debugfs_init();
>> 
>> 	debugfs_create_file("devices", 0444, root, NULL, &usbfs_devices_fops);
>> }
>> 
> I find a problem when move usb_debugfs_init() and usb_debugfs_cleanup()
> into usb common, it's easy to create "usb" directory, but difficult to
> cleanup it:
>
> common/common.c
>
> struct dentry *usb_debugfs_init(void)
> {
>     if (!usb_debug_root)
>         usb_debug_root = debugfs_create_dir("usb", NULL);
>
>     return usb_debug_root;
> }
>
> void usb_debugfs_cleanup(void)
> {
>     debugfs_remove_recursive(usb_debug_root);
>     usb_debug_root = NULL;
> }
>
> core/usb.c
>
> static void usb_core_debugfs_init(void)
> {
>     struct dentry *root = usb_debugfs_init();
>
>     debugfs_create_file("devices", 0444, root, NULL,
> &usbfs_devices_fops);
> }
>
> static int __init usb_init(void)
> {
>     ...
>     usb_core_debugfs_init();
>     ...
> }
>
> static void __exit usb_exit(void)
> {
>     ...
>     usb_debugfs_cleanup();
>     // will be error, gadget may use it.
>     ...
> }
>
> gadget/udc/core.c
>
> static int __init usb_udc_init(void)
> {
>     ...
>     usb_debugfs_init();
>     ...
> }
>
> static void __exit usb_udc_exit(void)
> {
>     ...
>     usb_debugfs_cleanup();
>     // can't cleanup in fact, usb core may use it.
> }
>
> How to handle this case? introduce a reference count? do you have any
> suggestion?

I guess a simple refcount is the way to go:

struct dentry *usb_debugfs_init(void)
{
	if (!usb_debug_root)
		usb_debug_root = debugfs_create_dir("usb", NULL);

	usb_debug_root_refcnt++;
	return usb_debug_root;
}

void usb_debugfs_cleanup(void)
{
	if (!(--usb_debug_root_refcnt)) {
		debugfs_remove_recursive(usb_debug_root);
		usb_debug_root = NULL;
	}
}

Or something along those lines

-- 
balbi