Re: [PATCH v17 1/7] usb: misc: Add onboard_usb_hub driver

[Matthias Kaehlcke <mka@chromium.org>]

On Thu, Nov 18, 2021 at 09:52:28AM -0800, Matthias Kaehlcke wrote:
> On Wed, Nov 17, 2021 at 04:11:34PM -0800, Doug Anderson wrote:
> > Hi,
> > 
> > On Tue, Nov 16, 2021 at 12:07 PM Matthias Kaehlcke <mka@chromium.org> wrote:
> > >
> > > --- a/drivers/usb/misc/Kconfig
> > > +++ b/drivers/usb/misc/Kconfig
> > > @@ -284,3 +284,20 @@ config BRCM_USB_PINMAP
> > >           This option enables support for remapping some USB external
> > >           signals, which are typically on dedicated pins on the chip,
> > >           to any gpio.
> > > +
> > > +config USB_ONBOARD_HUB
> > > +       tristate "Onboard USB hub support"
> > 
> > Aren't you back to shenanigans now that you're being called straight
> > from the USB core? What if you're a module and the USB core is
> > builtin? It can't call you, right? ...or what if you're builtin but
> > the USB core is a module (yeah, I know that sounds insane but I don't
> > think anything technically prevents it)?
> 
> Indeed, a dependency involving USB host mode is needed, as previously
> with xhci_plat.
> 
> > Can you just add a dependency here such that if the USB core is a
> > module that you're a module and if the USB core is builtin that you're
> > builtin?
> 
> I couldn't find a way to specify that in the config options of the driver
> itself. I fear the dependency has to be specified in CONFIG_USB, like it
> was done previously with USB_XHCI_PLATFORM:
> 
> https://patchwork.kernel.org/project/linux-usb/patch/20210813125146.v16.6.I7a3a7d9d2126c34079b1cab87aa0b2ec3030f9b7@changeid/
> 
> Hope that isn't controversial.

Ugh, actually adding

  depends on USB_ONBOARD_HUB || !USB_ONBOARD_HUB

to CONFIG_USB does not work. The problem is that USB_ONBOARD_HUB depends on
CONFIG_USB (not through an explicit dependency, but the 'misc' directory it
resides in is only included when CONFIG_USB=y/m), so the above rule would
introduce a circular dependency.

Unless there is some other way to specify "don't allow building
USB_ONBOARD_HUB as a module, unless USB is a module" I fear USB_ONBOARD_HUB
must be bool, which isn't really great :(