Re: [PATCH] misc: powermate: update the reference count of the usb interface structure

On Sun, Jul 25, 2021 at 12:56:37AM +0100, Salah Triki wrote:

Hi,

On Sat, Jul 24, 2021 at 04:08:02PM -0700, Dmitry Torokhov wrote:

quoted

On Sat, Jul 24, 2021 at 10:20:16PM +0100, Salah Triki wrote:

quoted

Use usb_get_intf() and usb_put_intf() in order to update the reference
count of the usb interface structure.

This is quite pointless as the driver will be unbound from the interface
before interface is deleted.

From the documentation of usb_get_intf():

[quote]

Each live reference to a interface must be refcounted.

Drivers for USB interfaces should normally record such references in their 
probe() methods, when they bind to an interface, and release them by calling
usb_put_intf(), in their disconnect() methods.

[/quote]

I see. In this case I recommend you submit a patch to the documentation
clarifying this, as taking a reference when binding to an interface
makes sense when dealing with a secondary interface, but not primary
one. See for example drivers/usb/class/cdc-acm.c where it binds to the
data interface, but also locates control interface and bumps up
reference to that.

As you may notice there is only a handful of drivers that use this API,
and as I am looking at them most do not actually need to use it.

Thanks.

-- 
Dmitry