linux-kernel - Re: [PATCH v15 3/4] xhci: sideband: add api to trace sideband usage

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Message-ID: <CAOuDEK2=UyjYbPQeSxVSmiLu6A36m4Tt9xADHyamJHM61-vhmQ@mail.gmail.com>
Date: Tue, 26 Aug 2025 12:37:00 +0800
From: Guan-Yu Lin <guanyulin@...gle.com>
To: Greg KH <gregkh@...uxfoundation.org>
Cc: mathias.nyman@...el.com, hannelotta@...il.com, zijun.hu@....qualcomm.com, 
	xu.yang_2@....com, stern@...land.harvard.edu, 
	andriy.shevchenko@...ux.intel.com, ben@...adent.org.uk, 
	quic_wcheng@...cinc.com, krzysztof.kozlowski@...aro.org, 
	dh10.jung@...sung.com, linux-usb@...r.kernel.org, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v15 3/4] xhci: sideband: add api to trace sideband usage

On Wed, Aug 13, 2025 at 10:51 PM Greg KH <gregkh@...uxfoundation.org> wrote:
>
> On Fri, Aug 01, 2025 at 03:39:32AM +0000, Guan-Yu Lin wrote:
> > +config USB_XHCI_SIDEBAND_SUSPEND
>
> Again, why is a new config option needed here?  Why can't we just use
> the existing one?  Why would you ever want one and not the other?
>
USB_XHCI_SIDEBAND focuses on the normal use case where the system is
active, while USB_XHCI_SIDEBAND_SUSPEND enables the sideband during
system sleep (Suspend-to-RAM). The design allows the user to determine
the degree of support for the sideband in the system. We could add the
"select" keyword to automatically enable USB_XHCI_SIDEBAND once
USB_XHCI_SIDEBAND_SUSPEND is enabled.
>
> > +EXPORT_SYMBOL_GPL(xhci_sideband_check);
> > +#endif /* IS_ENABLED(CONFIG_USB_XHCI_SIDEBAND_SUSPEND) */
>
> #ifdef in .c files is generally not a good idea, is it really needed
> here?  Maybe it is, it's hard to unwind...
>
> thanks,
>
> greg k-h

Given that CONFIG_USB_XHCI_SIDEBAND_SUSPEND depends on
CONFIG_USB_XHCI_SIDEBAND and adds only a single function, I think it
is preferable to place the new code in the same file. This approach
prevents unnecessary code fragmentation and improves maintainability
by keeping related functions together.

Regards,
Guan-Yu