Re: [PATCH] Bluetooth: btusb: avoid unused function warning

From: Arnd Bergmann <arnd@arndb.de>
To: Marcel Holtmann <marcel@holtmann.org>
Cc: Johan Hedberg <johan.hedberg@gmail.com>,
	Alex Lu <alex_lu@realsil.com.cn>,
	Matthias Kaehlcke <mka@chromium.org>,
	Rajat Jain <rajatja@google.com>,
	Raghuram Hegde <raghuram.hegde@intel.com>,
	Bluez mailing list <linux-bluetooth@vger.kernel.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] Bluetooth: btusb: avoid unused function warning
Date: Thu, 19 Sep 2019 14:26:55 +0200	[thread overview]
Message-ID: <CAK8P3a0AeGi2pd78A3yzh0NNGdgGvo_y1LCginyTCY3OUeVHkg@mail.gmail.com> (raw)
In-Reply-To: <C6D98BD8-F57F-411F-A2F2-D9E531137002@holtmann.org>

On Thu, Sep 19, 2019 at 9:32 AM Marcel Holtmann <marcel@holtmann.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@arndb.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@arndb.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