On Mon, Nov 04, 2019 at 06:50:01PM +0800, maowenan wrote:
> 
> 
> On 2019/11/4 18:04, Thierry Reding wrote:
> > On Mon, Nov 04, 2019 at 10:59:45AM +0800, Mao Wenan wrote:
> >> If CONFIG_USB_TEGRA_XUDC=y and CONFIG_USB_ROLE_SWITCH=m,
> >> 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_unregister'
> >> drivers/usb/gadget/udc/tegra-xudc.o: In function `tegra_xudc_probe':
> >> tegra-xudc.c:(.text+0x1b88): undefined reference to `usb_role_switch_register'
> >> 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'
> >>
> >> This patch add dependency USB_ROLE_SWITCH for UDC driver.
> >>
> >> Fixes: 49db427232fe ("usb: gadget: Add UDC driver for tegra XUSB device mode controller")
> >> Signed-off-by: Mao Wenan <maowenan@huawei.com>
> >> ---
> >>  drivers/usb/gadget/udc/Kconfig | 1 +
> >>  1 file changed, 1 insertion(+)
> >>
> >> diff --git a/drivers/usb/gadget/udc/Kconfig b/drivers/usb/gadget/udc/Kconfig
> >> 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.
> > 
> 
> Thanks, I send v2 and change 'depends on' to 'select' for this patch.

Great, can you also follow up with a patch to hide the USB_ROLE_SWITCH
option so that we can avoid any of the pitfalls associated with user-
visible symbols and "select"?

Thierry