Re: [PATCH v4 35/41] usb: uhci: handle HAS_IOPORT dependencies

From: Niklas Schnelle <schnelle@linux.ibm.com>
To: Arnd Bergmann <arnd@arndb.de>,
	Alan Stern <stern@rowland.harvard.edu>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: "Bjorn Helgaas" <bhelgaas@google.com>,
	"Uwe Kleine-König" <u.kleine-koenig@pengutronix.de>,
	"Mauro Carvalho Chehab" <mchehab@kernel.org>,
	"Rafael J . Wysocki" <rafael@kernel.org>,
	"Geert Uytterhoeven" <geert@linux-m68k.org>,
	"Paul Walmsley" <paul.walmsley@sifive.com>,
	"Palmer Dabbelt" <palmer@dabbelt.com>,
	"Albert Ou" <aou@eecs.berkeley.edu>,
	linux-kernel@vger.kernel.org,
	Linux-Arch <linux-arch@vger.kernel.org>,
	linux-pci@vger.kernel.org, "Arnd Bergmann" <arnd@kernel.org>,
	linux-usb@vger.kernel.org
Subject: Re: [PATCH v4 35/41] usb: uhci: handle HAS_IOPORT dependencies
Date: Fri, 19 May 2023 13:31:12 +0200	[thread overview]
Message-ID: <8d5f62aff02f0043c8f601f24c949c5fe03e132e.camel@linux.ibm.com> (raw)
In-Reply-To: <440855f4-897c-4597-bbe6-7c5f295f616a@app.fastmail.com>

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