linux-kernel - Re: [PATCH] staging: emxx_udc: Remove unused device

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Message-ID: <20181009130912.GA25423@kroah.com>
Date:   Tue, 9 Oct 2018 15:09:12 +0200
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Nick Desaulniers <ndesaulniers@...gle.com>
Cc:     Nathan Chancellor <natechancellor@...il.com>,
        devel@...verdev.osuosl.org, damm+renesas@...nsource.se,
        LKML <linux-kernel@...r.kernel.org>,
        Arnd Bergmann <arnd@...db.de>
Subject: Re: [PATCH] staging: emxx_udc: Remove unused device_desc declaration

On Fri, Oct 05, 2018 at 02:05:45PM -0700, Nick Desaulniers wrote:
> On Wed, Oct 3, 2018 at 10:56 PM Nathan Chancellor
> <natechancellor@...il.com> wrote:
> >
> > Clang warns:
> >
> > drivers/staging/emxx_udc/emxx_udc.c:1373:37: warning: variable
> > 'device_desc' is not needed and will not be emitted
> > [-Wunneeded-internal-declaration]
> > static struct usb_device_descriptor device_desc = {
> >                                     ^
> > 1 warning generated.
> >
> > This definition hasn't been attached to anything since the driver was
> > introduced in commit 33aa8d45a4fe ("staging: emxx_udc: Add Emma Mobile
> > USB Gadget driver") and neither GCC nor Clang emit any reference to the
> > variable in the final assembly. The only reason GCC doesn't warn about
> > this variable being unused is the sizeof function.
> >
> > Reported-by: Nick Desaulniers <ndesaulniers@...gle.com>
> > Signed-off-by: Nathan Chancellor <natechancellor@...il.com>
> > ---
> >
> > This seems kind of wrong given this is a USB driver but there isn't an
> > instance of a platform_driver in the kernel tree having a usb device
> > descriptor declaration so I'm unsure of how to handle this warning aside
> > from just removing the definition but I'm certainly open to suggestions.
> 
> In drivers under drivers/usb/gadget/legacy/{ether|mass_storage|hid}.c,
> it seems that addresses of instances of `struct usb_device_descriptor`
> are stored in instances of `struct usb_composite_driver eth_driver`
> that are passed to module_usb_composite_driver().
> 
> drivers/staging/emxx_udc/emxx_udc.c doesn't mention anything about
> being a composite driver, and I don't know if there are multiple
> devices to warrant a composite driver?  Composite seems to imply "more
> than one gadget" while the path to drivers using this interface under
> drivers/usb/gadget/legacy/ seem to imply there's a modern (non-legacy)
> usb gadget interface that could potentially be used instead.
> 
> If this was never intended to be a composite usb driver, or there's
> some reason why it doesn't make sense for it to be one, then this code
> is likely dead and your fix is correct.  If it's not, maybe folks who
> know more about the USB interfaces have another solution to make this
> a composite usb driver?

I'll take the patch, the code looks wrong, it should not be needed here.

thanks,

greg k-h