linux-kernel - Re: [PATCH] usb: core: Call disconnect() only if it is provided by driver

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Message-ID: <36a83342-6c30-73a1-7759-971d2134420a@gmail.com>
Date:   Thu, 19 May 2022 20:13:53 +0300
From:   Dmytro Bagrii <dimich.dmb@...il.com>
To:     Greg KH <gregkh@...uxfoundation.org>
Cc:     Alan Stern <stern@...land.harvard.edu>,
        Oliver Neukum <oneukum@...e.com>, linux-usb@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] usb: core: Call disconnect() only if it is provided by
 driver

On 19.05.22 19:38, Greg KH wrote:
> On Thu, May 19, 2022 at 06:27:17PM +0300, Dmytro Bagrii wrote:
>> On 19.05.22 16:45, Greg KH wrote:
>>> On Thu, May 19, 2022 at 04:29:00PM +0300, Dmytro Bagrii wrote:
>>>> A driver may use devres allocations. Disconnect handler is not needed in
>>>> this case. Allow such driver to leave .disconnect field uninitialized in
>>>> struct usb_driver instead of providing empty stub function.
>>>>
>>>> Signed-off-by: Dmytro Bagrii <dimich.dmb@...il.com>
>>>> ---
>>>>  drivers/usb/core/driver.c | 3 ++-
>>>>  1 file changed, 2 insertions(+), 1 deletion(-)
>>>>
>>>> diff --git a/drivers/usb/core/driver.c b/drivers/usb/core/driver.c
>>>> index 355ed33a2179..d7fe440b033c 100644
>>>> --- a/drivers/usb/core/driver.c
>>>> +++ b/drivers/usb/core/driver.c
>>>> @@ -455,7 +455,8 @@ static int usb_unbind_interface(struct device *dev)
>>>>  	if (!driver->soft_unbind || udev->state == USB_STATE_NOTATTACHED)
>>>>  		usb_disable_interface(udev, intf, false);
>>>>  
>>>> -	driver->disconnect(intf);
>>>> +	if (driver->disconnect)
>>>> +		driver->disconnect(intf);
>>>>  
>>>>  	/* Free streams */
>>>>  	for (i = 0, j = 0; i < intf->cur_altsetting->desc.bNumEndpoints; i++) {
>>>> -- 
>>>> 2.36.1
>>>>
>>>
>>> What in-kernel driver has this issue and does not have a disconnect
>>> callback?
>>
>> I don't see such in-kernel USB drivers yet.
> 
> Great, then all is well.  We can not make kernel changes for out-of-tree
> drivers for obvious reasons.
> 
> When you submit your driver, we will be glad to consider this change.
> But as others changed, odds are your driver is incorrect and should have
> a disconnect call.  Unless it is a very simple driver that could be done
> instead in userspace with usbfs/libusb?

Ok, i agree, my propoposed change is premature.
Of course, i'm checking the driver for memory, refcounts and other
resources leakage during development and not going to publish it until make
sure it works correctly.
There are some limitations with libusb in my case, e.g. it is unable to
bind existing in-tree drivers to a bus provided by hardware over USB.
Thank you for explanation.

-- 
Best Regards,
Dmytro Bagrii.