Re: [PATCH 1/4] PCI / ACPI: Identify external PCI devices

From: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
To: Mika Westerberg <mika.westerberg@linux.intel.com>
Cc: Lukas Wunner <lukas@wunner.de>,
	iommu@lists.linux-foundation.org, Joerg Roedel <joro@8bytes.org>,
	David Woodhouse <dwmw2@infradead.org>,
	Lu Baolu <baolu.lu@linux.intel.com>,
	Ashok Raj <ashok.raj@intel.com>,
	Bjorn Helgaas <bhelgaas@google.com>,
	"Rafael J. Wysocki" <rjw@rjwysocki.net>,
	Jacob jun Pan <jacob.jun.pan@intel.com>,
	Andreas Noever <andreas.noever@gmail.com>,
	Michael Jamet <michael.jamet@intel.com>,
	Yehezkel Bernat <YehezkelShB@gmail.com>,
	Christian Kellner <ckellner@redhat.com>,
	Mario.Limonciello@dell.com,
	Anthony Wong <anthony.wong@canonical.com>,
	linux-acpi@vger.kernel.org, linux-pci@vger.kernel.org,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH 1/4] PCI / ACPI: Identify external PCI devices
Date: Thu, 15 Nov 2018 17:46:08 +0000	[thread overview]
Message-ID: <20181115174608.GA17691@e107981-ln.cambridge.arm.com> (raw)
In-Reply-To: <20181115121627.GA2500@lahna.fi.intel.com>

On Thu, Nov 15, 2018 at 02:16:27PM +0200, Mika Westerberg wrote:
> On Thu, Nov 15, 2018 at 01:07:36PM +0100, Lukas Wunner wrote:
> > On Thu, Nov 15, 2018 at 01:37:37PM +0200, Mika Westerberg wrote:
> > > On Thu, Nov 15, 2018 at 11:13:56AM +0000, Lorenzo Pieralisi wrote:
> > > > I have strong objections to the way these bindings have been forced upon
> > > > everybody; if that's the way *generic* ACPI bindings are specified I
> > > > wonder why there still exists an ACPI specification and related working
> > > > group.
> > > > 
> > > > I personally (but that's Bjorn and Rafael choice) think that this is
> > > > not a change that belongs in PCI core, ACPI bindings are ill-defined
> > > > and device tree bindings are non-existing.
> > > 
> > > Any idea where should I put it then? These systems are already out there
> > > and we need to support them one way or another.
> > 
> > I suppose those are all Thunderbolt, so could be handled by the
> > existing ->is_thunderbolt bit?
> > 
> > It was said in this thread that ->is_external is more generic in
> > that it could also be used on PCIe slots, however that use case
> > doesn't appear to lend itself to the "plug in while laptop owner
> > is getting coffee" attack.  To access PCIe slots on a server you
> > normally need access to a data center.  On a desktop, you usually
> > have to open the case, by which time the coffee may already have
> > been fetched.  So frankly the binding seems a bit over-engineered
> > to me and yet another thing that BIOS writers may get wrong.
> 
> I would not say it should include PCIe slots but there are other cables
> that carry PCIe and I was thinking we could make it to support those as
> well.
> 
> I have no problem using is_thunderbolt here, though if we don't want to
> support non-Thunderbolt external devices this way.
> 
> However, the question here is more that where I should put the _DSD
> parsing code if it is not suitable to be placed inside PCI/ACPI core as
> I've done in this patch? ;-)

Do you really need to parse it if the dev->is_thunderbolt check is enough ?

Thanks,
Lorenzo