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

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Message-Id: <C6D98BD8-F57F-411F-A2F2-D9E531137002@holtmann.org>
Date:   Thu, 19 Sep 2019 09:32:33 +0200
From:   Marcel Holtmann <marcel@...tmann.org>
To:     Arnd Bergmann <arnd@...db.de>
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>,
        linux-bluetooth@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] Bluetooth: btusb: avoid unused function warning

Hi Arnd,

> 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.

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.

Regards

Marcel