From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <tglx@linutronix.de>
Return-Path: <tglx@linutronix.de>
Date: Wed, 24 Aug 2016 19:23:46 +0200 (CEST)
From: Thomas Gleixner <tglx@linutronix.de>
To: Jan Kiszka <jan.kiszka@siemens.com>
cc: Bjorn Helgaas <helgaas@kernel.org>, LKML <linux-kernel@vger.kernel.org>,
    x86@kernel.org, Bjorn Helgaas <bhelgaas@google.com>,
    linux-pci@vger.kernel.org, Benedikt Spranger <b.spranger@linutronix.de>,
    Lukas Wunner <lukas@wunner.de>
Subject: Re: x86/PCI: Scan all functions during probing
In-Reply-To: <73341fe4-9017-7dcb-7ae3-a993428c11fc@siemens.com>
Message-ID: <alpine.DEB.2.20.1608241923190.5714@nanos>
References: <alpine.DEB.2.20.1608091318530.5388@nanos> <20160809134452.GA27301@localhost> <20160818203348.GK27353@localhost> <alpine.DEB.2.20.1608241037510.5714@nanos> <73341fe4-9017-7dcb-7ae3-a993428c11fc@siemens.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=US-ASCII
List-ID: <linux-pci.vger.kernel.org>

On Wed, 24 Aug 2016, Jan Kiszka wrote:
> On 2016-08-24 04:39, Thomas Gleixner wrote:
> > On Thu, 18 Aug 2016, Bjorn Helgaas wrote:
> >> I looked up the spec: PCI (not PCIe) r3.0, sec 3.2.2.3.4, says:
> >>
> >>   A single-function device may optionally respond to all function
> >>   numbers as the same function or may ... respond only to function 0
> >>   and not respond to the other function numbers.
> >>
> >> I'm concerned that a single-function device that responds to all
> >> function numbers might break with this patch.
> >>
> >>   [multi-function devices] are also required to always implement
> >>   function 0 in the device.
> >>
> >> Here's the reason we can advance by 8 in the "Go find them" loop.
> >>
> >>   If a single function device is detected (i.e., bit 7 in the Header
> >>   Type register of function 0 is 0), no more functions for that Device
> >>   Number will be checked.  If a multi-function device is detected
> >>   (i.e., bit 7 in the Header Type register of function 0 is 1), then
> >>   all remaining Function Numbers will be checked.
> >>
> >> This patch does the opposite of what the first sentence recommends.
> > 
> > Fair enough. We'll need to find a way to deal with that in jailhouse then.
> 
> Wouldn't it also be an option to have this fine-grained scanning only
> activated if we detect to run over Jailhouse (which we have to anyway)?
> Such code hasn't been proposed for upstream yet, but we will eventually.

That might be an option.

Thanks,

	tglx