linux-kernel - Re: [PATCH v4 05/41] counter: add HAS

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Message-ID: <ZGtO1U7Wx7MVi0DL@fedora>
Date:   Mon, 22 May 2023 07:15:33 -0400
From:   William Breathitt Gray <william.gray@...aro.org>
To:     Niklas Schnelle <schnelle@...ux.ibm.com>
Cc:     Arnd Bergmann <arnd@...db.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Uwe Kleine-König 
        <u.kleine-koenig@...gutronix.de>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Alan Stern <stern@...land.harvard.edu>,
        "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@...r.kernel.org,
        linux-pci@...r.kernel.org, Arnd Bergmann <arnd@...nel.org>,
        linux-iio@...r.kernel.org,
        Jonathan Cameron <Jonathan.Cameron@...wei.com>
Subject: Re: [PATCH v4 05/41] counter: add HAS_IOPORT dependencies

On Mon, May 22, 2023 at 12:42:15PM +0200, Niklas Schnelle wrote:
> On Fri, 2023-05-19 at 10:21 -0400, William Breathitt Gray wrote:
> > On Fri, May 19, 2023 at 03:39:57PM +0200, Niklas Schnelle wrote:
> > > On Fri, 2023-05-19 at 15:38 +0200, Niklas Schnelle wrote:
> > > > On Fri, 2023-05-19 at 15:17 +0200, Niklas Schnelle wrote:
> > > > > On Thu, 2023-05-18 at 21:26 -0400, William Breathitt Gray wrote:
> > > > > > On Tue, May 16, 2023 at 01:00:01PM +0200, Niklas Schnelle wrote:
> > > > > > > In a future patch HAS_IOPORT=n will result in inb()/outb() and friends
> > > > > > > not being declared. We thus need to add HAS_IOPORT as dependency for
> > > > > > > those drivers using them.
> > > > > > > 
> > > > > > > Co-developed-by: Arnd Bergmann <arnd@...nel.org>
> > > > > > > Signed-off-by: Arnd Bergmann <arnd@...nel.org>
> > > > > > > Signed-off-by: Niklas Schnelle <schnelle@...ux.ibm.com>
> > > > > > 
> > > > > > Hi Niklas,
> > > > > > 
> > > > > > The change itself is fine, but please update the description to reflect
> > > > > > that this is adding a depends on HAS_IOPORT_MAP rather than HAS_IOPORT,
> > > > > > along with the reason why it's needed (i.e. devm_ioport_map() is used).
> > > > > > 
> > > > > > Thanks,
> > > > > > 
> > > > > > William Breathitt Gray
> > > > > > 
> > > > > > 
> > > > > 
> > > > > Right, this clearly needs adjustment. I went with the following commit
> > > > > message for v5:
> > > > > 
> > > > > "counter: add HAS_IOPORT_MAP dependency
> > > > > 
> > > > > The 104_QUAD_8 counter driver uses devm_ioport_map() without depending
> > > > > on HAS_IOPORT_MAP. This causes compilation to fail on platforms such as
> > > > > s390 which do not support I/O port mapping. Add the missing
> > > > > HAS_IOPORT_MAP dependency to fix this."
> > > > > 
> > > > 
> > > > Just noticed this isn't entirely correct. As devm_ioport_map() has an
> > > > empty stub for HAS_IOPORT_MAP=n this doesn't lead to a compile error it
> > > > just doesn't work. Will reword to "This causes the driver to not be
> > > > useable on platforms ..."
> > > 
> > > s/useable/usable/
> > 
> > 104_QUAD_8 has an explicit dependency on PC104 and X86, so I don't think
> > it would ever be used outside of x86 platforms. Does it still make sense
> > to have the HAS_IOPORT_MAP dependency in this case?
> > 
> > William Breathitt Gray
> 
> Well, yes and no, you're right that it doesn't really cause compile
> issues despite the "|| COMPILE_TEST" albeit the code could never work.
> Still, I'd add the dependency. At the very least it serves as
> documentation and maybe in the future someone will want to remove those
> empty stubs for HAS_IOPORT_MAP=n.
> 
> Thanks
> Niklas

Sure, that reasoning makes sense to me too, so let's go with the
explicit depends afterall.

By the way, I noticed two other modules that call devm_ioport_map() but
seem to be missing the HAS_IOPORT_MAP depends lines: the
drivers/iio/addac/stx104.c and drivers/iio/dac/cio-dac.c drivers. Do
these need respective patches as well?

As an aside, I haven't been following the previous patchsets closely so
forgive me if this has already been discussed in another thread: why
doesn't X86 automatically select HAS_IOPORT? Are there x86 platforms
that do not support ioport?

William Breathitt Gray

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