linux-kernel - Re: [PATCH v4 35/41] usb: uhci: handle HAS

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Message-ID: <8d5f62aff02f0043c8f601f24c949c5fe03e132e.camel@linux.ibm.com>
Date:   Fri, 19 May 2023 13:31:12 +0200
From:   Niklas Schnelle <schnelle@...ux.ibm.com>
To:     Arnd Bergmann <arnd@...db.de>,
        Alan Stern <stern@...land.harvard.edu>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Bjorn Helgaas <bhelgaas@...gle.com>,
        Uwe Kleine-König 
        <u.kleine-koenig@...gutronix.de>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        "Rafael J . Wysocki" <rafael@...nel.org>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        linux-kernel@...r.kernel.org,
        Linux-Arch <linux-arch@...r.kernel.org>,
        linux-pci@...r.kernel.org, Arnd Bergmann <arnd@...nel.org>,
        linux-usb@...r.kernel.org
Subject: Re: [PATCH v4 35/41] usb: uhci: handle HAS_IOPORT dependencies

On Wed, 2023-05-17 at 14:17 +0200, Arnd Bergmann wrote:
> On Tue, May 16, 2023, at 22:17, Alan Stern wrote:
> > On Tue, May 16, 2023 at 06:29:56PM +0200, Greg Kroah-Hartman wrote:
> > > On Tue, May 16, 2023 at 01:00:31PM +0200, Niklas Schnelle wrote:
> > 
> > > I'm confused now.
> > > 
> > > So if CONFIG_HAS_IOPORT is enabled, wonderful, all is good.
> > > 
> > > But if it isn't, then these are just no-ops that do nothing?  So then
> > > the driver will fail to work?  Why have these stubs at all?
> > > 
> > > Why not just not build the driver at all if this option is not enabled?
> > 
> > I should add something to my previous email.  This particular section of 
> > code is protected by:
> > 
> > #ifndef CONFIG_USB_UHCI_SUPPORT_NON_PCI_HC
> > /* Support PCI only */
> > 
> > So it gets used only in cases where the driver supports just a PCI bus 
> > -- no other sorts of non-PCI on-chip devices.  But the preceding patch 
> > in this series changes the Kconfig file to say:
> > 
> >  config USB_UHCI_HCD
> > 	tristate "UHCI HCD (most Intel and VIA) support"
> > 	depends on (USB_PCI && HAS_IOPORT) || USB_UHCI_SUPPORT_NON_PCI_HC
> > 
> > As a result, when the configuration includes support only for PCI 
> > controllers the driver won't get built unless HAS_IOPORT is set.  Thus 
> > the no-op case (in this part of the code) can't arise.
> 
> Indeed, that makes sense.
> 
> > Which is a long-winded way of saying that you're right; the UHCI_IN() 
> > and UHCI_OUT() wrappers aren't needed in this part of the driver.  I 
> > guess Niklas put them in either for consistency with the rest of the 
> > code or because it didn't occur to him that they could be omitted.  (And 
> > I didn't spot it either.)
> 
> It's probably less confusing to leave out the PCI-only part of
> the patch then and only modify the generic portion.
> 
>       Arnd

Yes I agree that way the UHCI_IN/OUT() macro is also only used directly
in combination with uhci_has_pci_registers(). I've done this for v5.

Thanks,
Niklas