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Date:   Mon, 4 Nov 2019 11:04:10 +0100
From:   Thierry Reding <treding@nvidia.com>
To:     Mao Wenan <maowenan@huawei.com>
CC:     <felipe.balbi@linux.intel.com>, <gregkh@linuxfoundation.org>,
        <nkristam@nvidia.com>, <arnd@arndb.de>, <johan@kernel.org>,
        <krzk@kernel.org>, <linux-usb@vger.kernel.org>,
        <linux-kernel@vger.kernel.org>, <kernel-janitors@vger.kernel.org>
Subject: Re: [PATCH -next] usb: gadget: Add dependency for USB_TEGRA_XUDC
Message-ID: <20191104100410.GB996639@ulmo>
References: <20191104025945.172620-1-maowenan@huawei.com>
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On Mon, Nov 04, 2019 at 10:59:45AM +0800, Mao Wenan wrote:
> If CONFIG_USB_TEGRA_XUDC=3Dy and CONFIG_USB_ROLE_SWITCH=3Dm,
> below erros can be seen:
> drivers/usb/gadget/udc/tegra-xudc.o: In function `tegra_xudc_remove':
> tegra-xudc.c:(.text+0x6b0): undefined reference to `usb_role_switch_unreg=
ister'
> drivers/usb/gadget/udc/tegra-xudc.o: In function `tegra_xudc_probe':
> tegra-xudc.c:(.text+0x1b88): undefined reference to `usb_role_switch_regi=
ster'
> drivers/usb/gadget/udc/tegra-xudc.o: In function `tegra_xudc_usb_role_sw_=
work':
> tegra-xudc.c:(.text+0x5ecc): undefined reference to `usb_role_switch_get_=
role'
>=20
> This patch add dependency USB_ROLE_SWITCH for UDC driver.
>=20
> Fixes: 49db427232fe ("usb: gadget: Add UDC driver for tegra XUSB device m=
ode controller")
> Signed-off-by: Mao Wenan <maowenan@huawei.com>
> ---
>  drivers/usb/gadget/udc/Kconfig | 1 +
>  1 file changed, 1 insertion(+)
>=20
> diff --git a/drivers/usb/gadget/udc/Kconfig b/drivers/usb/gadget/udc/Kcon=
fig
> index acaec3a..d103154 100644
> --- a/drivers/usb/gadget/udc/Kconfig
> +++ b/drivers/usb/gadget/udc/Kconfig
> @@ -445,6 +445,7 @@ config USB_TEGRA_XUDC
>  	tristate "NVIDIA Tegra Superspeed USB 3.0 Device Controller"
>  	depends on ARCH_TEGRA || COMPILE_TEST
>  	depends on PHY_TEGRA_XUSB
> +	depends on USB_ROLE_SWITCH

It looks like most other drivers that use the USB role switch class do
"select" here. Now, that's suboptimal because USB_ROLE_SWITCH is a user-
visible symbol, which can lead to conflicts, so it should be avoided. I
think that in this case it might make sense to hide USB_ROLE_SWITCH and
then convert all "depends on USB_ROLE_SWITCH" occurrences to "select
USB_ROLE_SWITCH". The USB role switch class is, after all, not useful by
itself. It always needs a host and/or gadget driver to make use of it.

Thierry

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