linux-kernel - Re: x86/PCI: Scan all functions during probing

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Message-ID: <alpine.DEB.2.20.1608241037510.5714@nanos>
Date:   Wed, 24 Aug 2016 10:39:11 +0200 (CEST)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Bjorn Helgaas <helgaas@...nel.org>
cc:     LKML <linux-kernel@...r.kernel.org>, x86@...nel.org,
        Bjorn Helgaas <bhelgaas@...gle.com>, linux-pci@...r.kernel.org,
        Jan Kiszka <jan.kiszka@...mens.com>,
        Benedikt Spranger <b.spranger@...utronix.de>,
        Lukas Wunner <lukas@...ner.de>
Subject: Re: x86/PCI: Scan all functions during probing

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.

Thanks,

	tglx