linux-kernel - Re: [PATCH] HID: wacom: add USB

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Message-ID: <CANRwn3TcLOgW9E=Sauj8-14d834FKegUXO7cw_ekJNhyLVR7=g@mail.gmail.com>
Date:   Fri, 28 Jul 2017 07:24:26 -0700
From:   Jason Gerecke <killertofu@...il.com>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     Jiri Kosina <jikos@...nel.org>,
        Jason Gerecke <jason.gerecke@...om.com>,
        Benjamin Tissoires <benjamin.tissoires@...hat.com>,
        "open list:HID CORE LAYER" <linux-input@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] HID: wacom: add USB_HID dependency

On Fri, Jul 28, 2017 at 7:18 AM, Arnd Bergmann <arnd@...db.de> wrote:
> On Fri, Jul 28, 2017 at 4:07 PM, Jason Gerecke <killertofu@...il.com> wrote:
>> On July 28, 2017 6:18:00 AM PDT, Arnd Bergmann <arnd@...db.de> wrote:
>>>The driver has gained a compile-time dependency that we should
>>>express in Kconfig to avoid this link error:
>>>
>>
>> Would conditional compilation be an acceptable alternative to adding
>> a dependency? The USB_HID code is only used to check if the driver
>> is working with a USB device. With USB_HID disabled, there's no need
>> for the check so there's no need for the dependency.
>
> I think that should work, e.g. you could replace the hid_is_using_ll_driver
> and 'extern' defintions with a helper per ll-driver like
>
> #ifdef CONFIG_USB_HID
> extern bool hid_is_using_usb_driver(struct hid_device *hdev)
> #else
> static inline bool hid_is_using_usb_driver(struct hid_device *hdev)
> {
>        return false;
> }
> #endif
>
> but is it worth it to avoid the dependency?
>
>        Arnd

I was thinking something more along the lines of the following since
the idea of per-transport helper functions was dismissed earlier:

#ifdef CONFIG_USB_HID
                if (hid_is_using_ll_driver(wacom->hdev, &usb_hid_driver)) {
[...]
                }
#endif

Jason