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

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

[Salah Triki]

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

Signed-off-by: Salah Triki <salah.triki@gmail.com>
---
 drivers/input/misc/powermate.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/input/misc/powermate.c b/drivers/input/misc/powermate.c
index c4e0e1886061..69dc3347478a 100644
--- a/drivers/input/misc/powermate.c
+++ b/drivers/input/misc/powermate.c
@@ -337,7 +337,7 @@ static int powermate_probe(struct usb_interface *intf, const struct usb_device_i
 		goto fail3;
 
 	pm->udev = udev;
-	pm->intf = intf;
+	pm->intf = usb_get_intf(intf);
 	pm->input = input_dev;
 
 	usb_make_path(udev, pm->phys, sizeof(pm->phys));
@@ -428,6 +428,7 @@ static void powermate_disconnect(struct usb_interface *intf)
 		usb_free_urb(pm->irq);
 		usb_free_urb(pm->config);
 		powermate_free_buffers(interface_to_usbdev(intf), pm);
+		usb_put_intf(pm->intf);
 
 		kfree(pm);
 	}
-- 
2.25.1

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

[Dmitry Torokhov]

Hi,

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

> 
> Signed-off-by: Salah Triki <salah.triki@gmail.com>
> ---
>  drivers/input/misc/powermate.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/input/misc/powermate.c b/drivers/input/misc/powermate.c
> index c4e0e1886061..69dc3347478a 100644
> --- a/drivers/input/misc/powermate.c
> +++ b/drivers/input/misc/powermate.c
> @@ -337,7 +337,7 @@ static int powermate_probe(struct usb_interface *intf, const struct usb_device_i
>  		goto fail3;
>  
>  	pm->udev = udev;
> -	pm->intf = intf;
> +	pm->intf = usb_get_intf(intf);
>  	pm->input = input_dev;
>  
>  	usb_make_path(udev, pm->phys, sizeof(pm->phys));
> @@ -428,6 +428,7 @@ static void powermate_disconnect(struct usb_interface *intf)
>  		usb_free_urb(pm->irq);
>  		usb_free_urb(pm->config);
>  		powermate_free_buffers(interface_to_usbdev(intf), pm);
> +		usb_put_intf(pm->intf);
>  
>  		kfree(pm);
>  	}
> -- 
> 2.25.1
> 

Thanks.

-- 
Dmitry

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

[Salah Triki]

Hi,

On Sat, Jul 24, 2021 at 04:08:02PM -0700, Dmitry Torokhov wrote:
> 
> On Sat, Jul 24, 2021 at 10:20:16PM +0100, Salah Triki wrote:
> > 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]

Thanx

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

[Dmitry Torokhov]

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