From: Lukas Wunner <lukas@wunner.de>
To: Ingo Molnar <mingo@kernel.org>
Cc: Bjorn Helgaas <helgaas@kernel.org>,
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>,
Matt Fleming <matt@codeblueprint.co.uk>,
Peter Zijlstra <peterz@infradead.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Linus Torvalds <torvalds@linux-foundation.org>,
Matthew Garrett <mjg59@srcf.ucam.org>,
m@bues.ch,
"linux-tip-commits@vger.kernel.org"
<linux-tip-commits@vger.kernel.org>
Subject: Re: [tip:x86/urgent] x86/quirks: Add early quirk to reset Apple AirPort card
Date: Fri, 10 Jun 2016 15:59:04 +0200 [thread overview]
Message-ID: <20160610135904.GA19958@wunner.de> (raw)
In-Reply-To: <20160610125957.GA30577@gmail.com>
On Fri, Jun 10, 2016 at 02:59:57PM +0200, Ingo Molnar wrote:
> * 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.
If I may add some additional information:
drivers/pci/probe.c contains the following comment:
/*
* The bus might already exist for two reasons: Either we are
* rescanning the bus or the bus is reachable through more than
* one bridge. The second case can happen with the i450NX
* chipset.
*/
So buses reachable through more than one bridge do exist, albeit they're
assumedly rare. The question is, what are the consequences?
(1) A minimal performance hit from scanning the bus multiple times.
(2) Quirks for devices on that bus are executed multiple times.
As said quirks can set QFLAG_APPLY_ONCE to prevent that. If it turns
out this patch regresses because quirks are executed multiple times
but shouldn't, that's a bug in those quirks and they need to be
amended to set QFLAG_APPLY_ONCE. If we avoid scanning the bus
multiple times, we'd essentially be papering over those bugs.
Best regards,
Lukas
next prev parent reply other threads:[~2016-06-10 13:55 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-05-28 23:35 [PATCH] x86: Add early quirk to reset Apple AirPort card Lukas Wunner
2016-06-02 9:48 ` Matt Fleming
2016-06-08 14:23 ` [tip:x86/urgent] x86/quirks: " tip-bot for Lukas Wunner
2016-06-08 18:56 ` Yinghai Lu
2016-06-08 20:09 ` Lukas Wunner
2016-06-09 6:48 ` Ingo Molnar
2016-06-09 11:04 ` Lukas Wunner
2016-06-09 16:37 ` Yinghai Lu
2016-06-09 20:20 ` Lukas Wunner
2016-06-10 0:04 ` Yinghai Lu
2016-06-10 11:58 ` Ingo Molnar
2016-06-10 12:16 ` Lukas Wunner
2016-06-10 12:59 ` Ingo Molnar
2016-06-10 13:59 ` Lukas Wunner [this message]
2016-06-10 20:08 ` Bjorn Helgaas
2016-06-12 11:13 ` Lukas Wunner
2016-06-09 22:57 ` [PATCH] x86: " Bjorn Helgaas
2016-06-12 10:31 [PATCH v2 3/3] x86/quirks: " Lukas Wunner
2016-07-10 19:01 ` [tip:x86/urgent] " tip-bot for Lukas Wunner
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