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

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Message-ID: <BC567D27D6B7384F84318942321624DE269180F9@hasmsx109.ger.corp.intel.com>
Date:	Sun, 18 Jan 2015 14:16:26 +0000
From:	"Jamet, Michael" <michael.jamet@...el.com>
To:	Andreas Noever <andreas.noever@...il.com>
CC:	Andy Shevchenko <andy.shevchenko@...il.com>,
	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>,
	Mika Westerberg <mika.westerberg@...ux.intel.com>
Subject: RE: [PATCH] pci: support Thunderbolt requirements for I/O resources.

> -----Original Message-----
> From: Andreas Noever [mailto:andreas.noever@...il.com]
> Sent: Tuesday, November 18, 2014 17:48
> To: Jamet, Michael
> Cc: Andy Shevchenko; Bjorn Helgaas; 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 Tue, Nov 18, 2014 at 9:20 AM, Jamet, Michael <michael.jamet@...el.com>
> wrote:
> >> -----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.
> 
> Now I am slightly confused. Does the BIOS (on non Apple hardware) leave I/O
> resources always unassigned? Your first post seemed to imply that it does
> assign some and that we should not interfere. In that case we would have to
> assign them on Apple systems ourselves. On the other hand if no TB device uses
> I/O resources and the BIOS never assigns them, then why do devices fail if we
> exhaust them?
> 
> Andreas

Correct. The BIOS may play a role in allocation of memory and I/O 
resources but most of the case will leave the I/O  resources unassigned.
Some legacy Thunderbolt devices are designed with I/O BARs, so they 
need to be handled with care as written in the other email thread to Bjorn.

/Michael
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