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

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Message-ID: <CAOuDEK3UR6ksPSfq02CvBcqcG+1G43UdofNp6ZmpZm0PSB77oA@mail.gmail.com>
Date: Thu, 11 Sep 2025 11:56:00 +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 2/4] usb: offload: add apis for offload usage tracking

On Sat, Sep 6, 2025 at 9:13 PM Greg KH <gregkh@...uxfoundation.org> wrote:
>
> 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

Thanks for the suggestions. I'll use only USB_XHCI_SIDEBAND_SUSPEND to
control all the features, including the core USB functions.

Regards,
Guan-Yu