linux-kernel - Re: [PATCH] Bluetooth: btusb: avoid unused function warning

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Message-ID: <CAK8P3a0AeGi2pd78A3yzh0NNGdgGvo_y1LCginyTCY3OUeVHkg@mail.gmail.com>
Date:   Thu, 19 Sep 2019 14:26:55 +0200
From:   Arnd Bergmann <arnd@...db.de>
To:     Marcel Holtmann <marcel@...tmann.org>
Cc:     Johan Hedberg <johan.hedberg@...il.com>,
        Alex Lu <alex_lu@...lsil.com.cn>,
        Matthias Kaehlcke <mka@...omium.org>,
        Rajat Jain <rajatja@...gle.com>,
        Raghuram Hegde <raghuram.hegde@...el.com>,
        Bluez mailing list <linux-bluetooth@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] Bluetooth: btusb: avoid unused function warning

On Thu, Sep 19, 2019 at 9:32 AM Marcel Holtmann <marcel@...tmann.org> wrote:
>
> > The btusb_rtl_cmd_timeout() function is used inside of an
> > ifdef, leading to a warning when this part is hidden
> > from the compiler:
> >
> > drivers/bluetooth/btusb.c:530:13: error: unused function 'btusb_rtl_cmd_timeout' [-Werror,-Wunused-function]
> >
> > Use an IS_ENABLED() check instead so the compiler can see
> > the code and then discard it silently.
> >
> > Fixes: d7ef0d1e3968 ("Bluetooth: btusb: Use cmd_timeout to reset Realtek device")
> > Signed-off-by: Arnd Bergmann <arnd@...db.de>
> > ---
> > drivers/bluetooth/btusb.c | 5 ++---
> > 1 file changed, 2 insertions(+), 3 deletions(-)
> >
> > diff --git a/drivers/bluetooth/btusb.c b/drivers/bluetooth/btusb.c
> > index a9c35ebb30f8..23e606aaaea4 100644
> > --- a/drivers/bluetooth/btusb.c
> > +++ b/drivers/bluetooth/btusb.c
> > @@ -3807,8 +3807,8 @@ static int btusb_probe(struct usb_interface *intf,
> >               btusb_check_needs_reset_resume(intf);
> >       }
> >
> > -#ifdef CONFIG_BT_HCIBTUSB_RTL
> > -     if (id->driver_info & BTUSB_REALTEK) {
> > +     if (IS_ENABLED(CONFIG_BT_HCIBTUSB_RTL) &&
> > +         (id->driver_info & BTUSB_REALTEK)) {
> >               hdev->setup = btrtl_setup_realtek;
> >               hdev->shutdown = btrtl_shutdown_realtek;
> >               hdev->cmd_timeout = btusb_rtl_cmd_timeout;
> > @@ -3819,7 +3819,6 @@ static int btusb_probe(struct usb_interface *intf,
> >                */
> >               set_bit(BTUSB_WAKEUP_DISABLE, &data->flags);
> >       }
> > -#endif
>
> I prefer that we stick another ifdef around the btusb_rtl_cmd_timeout function since that
> is how we did it for the other vendors as well.

Ok. Can you just commit that with 'Reported-by: Arnd Bergmann <arnd@...db.de>'?

> However I start to wonder if we need all these vendor ifdef anyway. The vendor specific
> functions should turn into empty stubs if their support is not selected.

It just wastes a little bit of object code space, which my approach
above avoids.

I guess one could also be clever and redefine those macros like

#define BTUSB_REALTEK (IS_ENABLED(CONFIG_BT_HCIBTUSB_RTL) ? 0x20000 : 0)

so the if() section gets silently dropped, in addition to treating
zero like BTUSB_IGNORE.

      Arnd