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

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Message-ID: <20181115174608.GA17691@e107981-ln.cambridge.arm.com>
Date:   Thu, 15 Nov 2018 17:46:08 +0000
From:   Lorenzo Pieralisi <lorenzo.pieralisi@....com>
To:     Mika Westerberg <mika.westerberg@...ux.intel.com>
Cc:     Lukas Wunner <lukas@...ner.de>, iommu@...ts.linux-foundation.org,
        Joerg Roedel <joro@...tes.org>,
        David Woodhouse <dwmw2@...radead.org>,
        Lu Baolu <baolu.lu@...ux.intel.com>,
        Ashok Raj <ashok.raj@...el.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Jacob jun Pan <jacob.jun.pan@...el.com>,
        Andreas Noever <andreas.noever@...il.com>,
        Michael Jamet <michael.jamet@...el.com>,
        Yehezkel Bernat <YehezkelShB@...il.com>,
        Christian Kellner <ckellner@...hat.com>,
        Mario.Limonciello@...l.com,
        Anthony Wong <anthony.wong@...onical.com>,
        linux-acpi@...r.kernel.org, linux-pci@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/4] PCI / ACPI: Identify external PCI devices

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