linux-kernel - Re: [PATCH v15 2/4] usb: offload: add apis for offload usage tracking

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Message-ID: <2025090650-decal-canary-8e34@gregkh>
Date: Sat, 6 Sep 2025 15:13:12 +0200
From: Greg KH <gregkh@...uxfoundation.org>
To: Guan-Yu Lin <guanyulin@...gle.com>
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 2/4] usb: offload: add apis for offload usage tracking

On Tue, Aug 26, 2025 at 11:59:00AM +0800, Guan-Yu Lin wrote:
> On Wed, Aug 13, 2025 at 10:50 PM Greg KH <gregkh@...uxfoundation.org> wrote:
> >
> > On Fri, Aug 01, 2025 at 03:39:31AM +0000, Guan-Yu Lin wrote:
> > > +
> > > +config USB_OFFLOAD
> > > +     bool "Enable USB offload feature"
> >
> > I'm confused, we already have a "USB offload feature" that went into the
> > last kernel release, why do we need a separate config option for this as
> > well?  Shouldn't this code only get built if the drivers that need it
> > select it automatically?  Forcing distros to configure this isn't
> > generally a good idea if at all possible.
> >
> 
> Based on the discussion in v13, a new, separate USB configuration
> option is required to avoid core USB functions being enabled or
> disabled via an xhci-specific option. The USB offload feature involves
> a sideband entity that can access xhci resources, which, from the USB
> driver's viewpoint, means USB transfers are offloaded to this other
> entity. Therefore, the name "USB_OFFLOAD" was chosen to reflect this
> functionality.

Again, you are increasing the number of config options here, which does
not make sense.  Why would anyone only want a subset, and not just the
whole thing?

Yes, USB_OFFLOAD only works today on xhci, and that's fine, so let's
just keep it that way.

> > > +     depends on USB
> > > +     depends on USB_XHCI_SIDEBAND_SUSPEND
> >
> > Especially because all "desktops" do not want this code selected, so
> > having it in all distros feels like a waste to me.
> >
> > thanks,
> >
> > greg k-h
> 
> For the config keywords, we could automatically select USB_OFFLOAD
> once USB_XHCI_SIDEBAND_SUSPEND is selected to reduce configuration
> efforts.

select is a nightmare to maintain and understand.  Please just reduce
configuration efforts by not adding new options at all :)

thanks,

greg k-h