linux-kernel - RE: [PATCH] pci: support Thunderbolt requirements for I/O resources.

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Date:	Tue, 18 Nov 2014 08:20:13 +0000
From:	"Jamet, Michael" <michael.jamet@...el.com>
To:	Andreas Noever <andreas.noever@...il.com>,
	Andy Shevchenko <andy.shevchenko@...il.com>
CC:	Bjorn Helgaas <bhelgaas@...gle.com>,
	"linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"Levy, Amir (Jer)" <amir.jer.levy@...el.com>,
	"Alloun, Dan" <dan.alloun@...el.com>,
	Rafael Wysocki <rjw@...ysocki.net>
Subject: RE: [PATCH] pci: support Thunderbolt requirements for I/O resources.

> -----Original Message-----
> From: Andreas Noever [mailto:andreas.noever@...il.com]
> Sent: Wednesday, November 12, 2014 22:19
> To: Andy Shevchenko
> Cc: Bjorn Helgaas; Jamet, Michael; linux-pci@...r.kernel.org; linux-
> kernel@...r.kernel.org; Levy, Amir (Jer); Alloun, Dan; Rafael Wysocki
> Subject: Re: [PATCH] pci: support Thunderbolt requirements for I/O
> resources.
> 
> On Wed, Nov 12, 2014 at 7:30 PM, Andy Shevchenko
> <andy.shevchenko@...il.com> wrote:
> > On Wed, Nov 12, 2014 at 7:29 PM, Bjorn Helgaas <bhelgaas@...gle.com>
> wrote:
> >
> > []
> >
> >>> To prevent this, we detect a chain contains a Thunderbolt device by
> >>> checking the Thunderbolt PCI device id.
> >>
> >> I'm really not happy about checking a list of device IDs to identify
> >> Thunderbolt devices.  Surely there's a better way, because a list
> >> like this has to be updated regularly.
> >
> > I recently proposed internally to use quirks (pci_fixup_early) for
> > that, but apparently Michael didn't have time to answer. It might be
> > he can just comment here since the patch already public.
> 
> In any case: this will interfere with thunderbolt hotplug on Apple systems,
> where we do not have BIOS support and have to handle hotplug events and
> assign resources ourselves. So please add a DMI check for Apple (the reverse
> of what we do in
> http://lxr.free-
> electrons.com/source/drivers/thunderbolt/nhi.c?v=3.17#L664
> ).
> 
> Thanks,
> Andreas

This is correct that the hotplug handling mechanism and interaction with BIOS is different. 
However, this patch also applies for any case, since the I/O space is limited 
and need to be preserved, so we must prevent allocation of I/O resources 
from the devices and avoiding exhaustion while chaining them.

Michael 


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