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Message-ID: <917b95c9af1b80843b8a361d1b7fa337a25105e7.camel@linux.ibm.com>
Subject: Re: [PATCH v3 35/38] video: handle HAS_IOPORT dependencies
From:   Niklas Schnelle <schnelle@linux.ibm.com>
To:     Ville =?ISO-8859-1?Q?Syrj=E4l=E4?= 
        <ville.syrjala@linux.intel.com>,
        Geert Uytterhoeven <geert@linux-m68k.org>
Cc:     linux-arch@vger.kernel.org, Arnd Bergmann <arnd@kernel.org>,
        linux-fbdev@vger.kernel.org, Albert Ou <aou@eecs.berkeley.edu>,
        Arnd Bergmann <arnd@arndb.de>,
        "Rafael J. Wysocki" <rafael@kernel.org>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Helge Deller <deller@gmx.de>,
        Paul Walmsley <paul.walmsley@sifive.com>,
        linux-pci@vger.kernel.org, linux-kernel@vger.kernel.org,
        dri-devel@lists.freedesktop.org,
        Alan Stern <stern@rowland.harvard.edu>,
        Uwe =?ISO-8859-1?Q?Kleine-K=F6nig?= 
        <u.kleine-koenig@pengutronix.de>,
        Bjorn Helgaas <bhelgaas@google.com>,
        Palmer Dabbelt <palmer@dabbelt.com>,
        Mauro Carvalho Chehab <mchehab@kernel.org>
Date:   Thu, 23 Mar 2023 15:17:38 +0100
In-Reply-To: <ZBGbxDWEhqr8hhgU@intel.com>
References: <20230314121216.413434-1-schnelle@linux.ibm.com>
         <20230314121216.413434-36-schnelle@linux.ibm.com>
         <CAMuHMdW4f8GJ-kFDPg6Ao=g3ZAXq79u9nUZ_dW1LonHu+vxk8Q@mail.gmail.com>
         <ZBGbxDWEhqr8hhgU@intel.com>
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On Wed, 2023-03-15 at 12:19 +0200, Ville Syrj=C3=A4l=C3=A4 wrote:
> On Wed, Mar 15, 2023 at 09:16:50AM +0100, Geert Uytterhoeven wrote:
> > Hi Niklas,
> >=20
> > On Tue, Mar 14, 2023 at 1:13=E2=80=AFPM Niklas Schnelle <schnelle@linux=
.ibm.com> wrote:
> > > In a future patch HAS_IOPORT=3Dn will result in inb()/outb() and frie=
nds
> > > not being declared. We thus need to add HAS_IOPORT as dependency for
> > > those drivers using them and guard inline code in headers.
> > >=20
> > > Co-developed-by: Arnd Bergmann <arnd@kernel.org>
> > > Signed-off-by: Niklas Schnelle <schnelle@linux.ibm.com>
> >=20
> > Thanks for your patch!
> >=20
> > > --- a/drivers/video/fbdev/Kconfig
> > > +++ b/drivers/video/fbdev/Kconfig
> >=20
> > > @@ -1284,7 +1285,7 @@ config FB_ATY128_BACKLIGHT
> > >=20
> > >  config FB_ATY
> > >         tristate "ATI Mach64 display support" if PCI || ATARI
> > > -       depends on FB && !SPARC32
> > > +       depends on FB && HAS_IOPORT && !SPARC32
> >=20
> > On Atari, this works without ATARI_ROM_ISA, hence it must not depend
> > on HAS_IOPORT.
> > The only call to inb() is inside a section protected by #ifdef
> > CONFIG_PCI. So:
>=20
> That piece of code is a nop anyway. We immediately overwrite
> clk_wr_offset with a hardcoded selection after the register reads.
> So if you nuke that nop code then no IOPORT dependency required
> at all.
>=20

I agree this "looks" like a nop but are we sure the inb() doesn't have
side effects?=C2=A0
(for reference drivers/video/fbdev/aty/aty/atyfb_base.c:
atyfb_setup_generc() towards the end)

It does feel a bit out of scope for this series but if it's really a
nop nuking it surely is the cleaner solution.

Thanks,
Niklas