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

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Date:   Thu, 19 May 2022 09:49:30 -0400
From:   Alan Stern <stern@...land.harvard.edu>
To:     Dmytro Bagrii <dimich.dmb@...il.com>
Cc:     gregkh@...uxfoundation.org, 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 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++) {

I'm very dubious about this change.  Disconnect routines generally do 
more than just deallocation.

Can you point to any drivers that would actually benefit from this?

Alan Stern