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Date: Fri, 10 Jun 2016 14:59:57 +0200
From: Ingo Molnar <mingo@kernel.org>
To: Lukas Wunner <lukas@wunner.de>, Bjorn Helgaas <helgaas@kernel.org>
Cc: Yinghai Lu <yinghai@kernel.org>, Thomas Gleixner <tglx@linutronix.de>,
        cmilsted@redhat.com, Rafa?? Mi??ecki <zajec5@gmail.com>,
        Bjorn Helgaas <bhelgaas@google.com>, "H. Peter Anvin" <hpa@zytor.com>,
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	<linux-tip-commits@vger.kernel.org>
Subject: Re: [tip:x86/urgent] x86/quirks: Add early quirk to reset Apple
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Message-ID: <20160610125957.GA30577@gmail.com>
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* Lukas Wunner <lukas@wunner.de> wrote:

> On Fri, Jun 10, 2016 at 01:58:45PM +0200, Ingo Molnar wrote:
> > * Yinghai Lu <yinghai@kernel.org> wrote:
> > > On 6/9/16, Lukas Wunner <lukas@wunner.de> wrote:
> > > > Well, the PCI core would also scan such a bus twice AFAICS.
> > > > And the performance penalty of scanning it twice seems negligible.
> > > > Early quirks can prevent double execution by setting QFLAG_APPLY_ONCE.
> > > > (Three quirks have set that flag already.)
> > > >
> > > > So I think this shouldn't be a concern.
> > > 
> > > I don't know. I would like see sth like following, and that is simple
> > > enough.
> > > 
> > > --- linux-2.6.orig/arch/x86/kernel/early-quirks.c
> > > +++ linux-2.6/arch/x86/kernel/early-quirks.c
> > > @@ -755,10 +755,16 @@ static int __init check_dev_quirk(int nu
> > >         return 0;
> > >  }
> > > 
> > > +static unsigned char __initdata scanned[256];
> > >  static void __init early_pci_scan_bus(int bus)
> > >  {
> > >         int slot, func;
> > > 
> > > +       if (scanned[bus])
> > > +               return;
> > > +
> > > +       scanned[bus] = 1;
> > > +
> > >         /* Poor man's PCI discovery */
> > >         for (slot = 0; slot < 32; slot++)
> > >                 for (func = 0; func < 8; func++) {
> > 
> > Ok, I removed the fix from tip:x86/urgent from the time being - could you
> > guys  please send a full version once a final approach is agreed upon?
> 
> IMHO the above patch to prevent double scanning isn't needed
> and less code is usually better. So my suggestion would be the
> patch as originally sent plus the delta fix I sent yesterday,
> either squashed or applied separately.
> 
> Since Yinghai Lu seems to disagree I guess you as the maintainer
> will have to make a decision. :-)

So I'd lean towards lower complexity, but since this is essentially PCI code I'd 
like to defer to Bjorn on that detail.

Thanks,

	Ingo