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

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Message-ID: <CAOuDEK3KZHgY7Z2mBOuEhuUn8eLfjS5BPcx3kaMqVYLUhOavWA@mail.gmail.com>
Date: Tue, 26 Aug 2025 11:59:00 +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 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.

>
> > +     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.

Regards,
Guan-Yu