linux-kernel - Re: [PATCH v9 2/2] usb: dwc3: Add Google Tensor SoC DWC3 glue driver

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Message-ID: <CA+zupgzL7v5MZDpxKDQQCqAZaqTdHbiG9-xTr+8RnigMFZJ_7Q@mail.gmail.com>
Date: Thu, 4 Dec 2025 23:14:39 -0800
From: Roy Luo <royluo@...gle.com>
To: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc: Rob Herring <robh@...nel.org>, Krzysztof Kozlowski <krzk+dt@...nel.org>, 
	Conor Dooley <conor+dt@...nel.org>, Peter Griffin <peter.griffin@...aro.org>, 
	André Draszik <andre.draszik@...aro.org>, 
	Tudor Ambarus <tudor.ambarus@...aro.org>, Thinh Nguyen <Thinh.Nguyen@...opsys.com>, 
	Philipp Zabel <p.zabel@...gutronix.de>, Badhri Jagan Sridharan <badhri@...gle.com>, 
	Doug Anderson <dianders@...gle.com>, linux-usb@...r.kernel.org, devicetree@...r.kernel.org, 
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org, 
	linux-samsung-soc@...r.kernel.org, Joy Chakraborty <joychakr@...gle.com>, 
	Naveen Kumar <mnkumar@...gle.com>
Subject: Re: [PATCH v9 2/2] usb: dwc3: Add Google Tensor SoC DWC3 glue driver

On Thu, Dec 4, 2025 at 10:05 PM Greg Kroah-Hartman
<gregkh@...uxfoundation.org> wrote:
>
> On Fri, Dec 05, 2025 at 02:26:38AM +0000, Roy Luo wrote:
> > +config USB_DWC3_GOOGLE
> > +     tristate "Google Platform"
> > +     depends on ARCH_GOOGLE || COMPILE_TEST
>
> There is no ARCH_GOOGLE in the tree now, so how is this supposed to
> work?  Shouldn't tools that check for "invalid config options" trigger
> on this?
>
> thanks,
>
> greg k-h

Hi Greg,

The menuconfig looks like the following and it doesn't complain:
| Symbol: ARCH_GOOGLE [=ARCH_GOOGLE]
| Type  : unknown
|
| Symbol: PHY_GOOGLE_USB [=y]
| Type  : tristate
| Defined at drivers/phy/Kconfig:104
|     Prompt: Google Tensor SoC USB PHY driver
|     Depends on: ARCH_GOOGLE || COMPILE_TEST [=y]

According to Kconfig documentation [1], the unknown symbol
would simply be evaluated as an "n", which is what we want.
"Convert the symbol into an expression. Boolean and tristate
symbols are simply converted into the respective expression
values. All other symbol types result in ‘n’."

In a different Kconfig documentation, an environment variable
"KCONFIG_WARN_UNKNOWN_SYMBOLS" is there to detect
undefined symbols in the "config input", but I can't find one that
catches undefined symbols in the Kconfig tree itself.

That is, the tool seems to allow this.
However, if this turns out to be a major problem. I think we
can either:
- Remove ARCH_GOOGLE and leave COMPILE_TEST as
  the only dependency. Then add ARCH_GOOGLE back
  later once it's in the tree.
- Defer the whole patch series until ARCH_GOOGLE is
  present (I hope not).

[1] https://docs.kernel.org/kbuild/kconfig-language.html#menu-dependencies
[2] https://www.kernel.org/doc/Documentation/kbuild/kconfig.rst

Regards,
Roy Luo