linux-kernel - Re: [PATCH v3 35/38] video: handle HAS

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Message-ID: <917b95c9af1b80843b8a361d1b7fa337a25105e7.camel@linux.ibm.com>
Date:   Thu, 23 Mar 2023 15:17:38 +0100
From:   Niklas Schnelle <schnelle@...ux.ibm.com>
To:     Ville Syrjälä 
        <ville.syrjala@...ux.intel.com>,
        Geert Uytterhoeven <geert@...ux-m68k.org>
Cc:     linux-arch@...r.kernel.org, Arnd Bergmann <arnd@...nel.org>,
        linux-fbdev@...r.kernel.org, Albert Ou <aou@...s.berkeley.edu>,
        Arnd Bergmann <arnd@...db.de>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Helge Deller <deller@....de>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org,
        dri-devel@...ts.freedesktop.org,
        Alan Stern <stern@...land.harvard.edu>,
        Uwe Kleine-König 
        <u.kleine-koenig@...gutronix.de>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>
Subject: Re: [PATCH v3 35/38] video: handle HAS_IOPORT dependencies

On Wed, 2023-03-15 at 12:19 +0200, Ville Syrjälä wrote:
> On Wed, Mar 15, 2023 at 09:16:50AM +0100, Geert Uytterhoeven wrote:
> > Hi Niklas,
> > 
> > On Tue, Mar 14, 2023 at 1:13 PM Niklas Schnelle <schnelle@...ux.ibm.com> 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 and guard inline code in headers.
> > > 
> > > Co-developed-by: Arnd Bergmann <arnd@...nel.org>
> > > Signed-off-by: Niklas Schnelle <schnelle@...ux.ibm.com>
> > 
> > Thanks for your patch!
> > 
> > > --- a/drivers/video/fbdev/Kconfig
> > > +++ b/drivers/video/fbdev/Kconfig
> > 
> > > @@ -1284,7 +1285,7 @@ config FB_ATY128_BACKLIGHT
> > > 
> > >  config FB_ATY
> > >         tristate "ATI Mach64 display support" if PCI || ATARI
> > > -       depends on FB && !SPARC32
> > > +       depends on FB && HAS_IOPORT && !SPARC32
> > 
> > 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:
> 
> 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.
> 

I agree this "looks" like a nop but are we sure the inb() doesn't have
side effects? 
(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