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

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Message-ID: <20181115111356.GA599@e107981-ln.cambridge.arm.com>
Date:   Thu, 15 Nov 2018 11:13:56 +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 12:22:39PM +0200, Mika Westerberg wrote:
> On Tue, Nov 13, 2018 at 11:45:36AM +0000, Lorenzo Pieralisi wrote:
> > On Tue, Nov 13, 2018 at 01:27:00PM +0200, Mika Westerberg wrote:
> > 
> > [...]
> > 
> > > > To be frank the concept (and Microsoft _DSD bindings) seems a bit vague
> > > > and not thoroughly defined and I would question its detection at
> > > > PCI/ACPI core level, I would hope this can be clarified at ACPI
> > > > specification level, at least.
> > > 
> > > I guess that is the way they envision to use _DSD. Instead of having
> > > single UUID that covers all properties (like what we have with device
> > > properties) they have one UUID per property "class". I certainly hope we
> > > don't need to keep extending prp_guids[] array each time they invent
> > > another "class" of properties.
> > 
> > It is even worse than that. This is a unilateral/obscure change that
> > won't be part of ACPI specifications (I guess it was easier to add a
> > UUID than add this to the ACPI specifications through the AWSG) but it
> > is still supposed to be applicable to ACPI PCI bindings on any
> > platforms/arches; this way of adding bindings does not work and it
> > has to be rectified.
> 
> I agree.
> 
> For the existing property "classes" such as the one here I don't think
> we can do anything. There are systems already with these included in
> their ACPI tables.
> 
> I wonder if you have any objections regarding this patch?

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.

At the very least Microsoft should be asked to publish and discuss
these bindings within the ACPI and UEFI forums.

Lorenzo