linux-kernel - Re: [PATCH] PCI: ACPI: Allow internal devices to be marked as untrusted

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Date:   Fri, 28 Jan 2022 09:55:32 +0000
From:   Jean-Philippe Brucker <jean-philippe@...aro.org>
To:     Rajat Jain <rajatja@...gle.com>
Cc:     "Rafael J. Wysocki" <rafael@...nel.org>,
        Mika Westerberg <mika.westerberg@...ux.intel.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Bjorn Helgaas <helgaas@...nel.org>,
        Len Brown <lenb@...nel.org>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
        Linux PCI <linux-pci@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Rajat Jain <rajatxjain@...il.com>,
        Dmitry Torokhov <dtor@...gle.com>,
        Jesse Barnes <jsbarnes@...gle.com>,
        Pavel Machek <pavel@...x.de>,
        Oliver O'Halloran <oohall@...il.com>,
        Joerg Roedel <joro@...tes.org>
Subject: Re: [PATCH] PCI: ACPI: Allow internal devices to be marked as
 untrusted

On Thu, Jan 27, 2022 at 02:26:07PM -0800, Rajat Jain wrote:
> > > > And shouldn't this be an ACPI standard?
> > >
> > > Probably should or some supplemental doc but not sure how easy these
> > > "properties" can be added there to be honest.
> 
> AIUI, the principal comment I have received here is that this property
> needs to be documented somewhere. I agree.
> 
> Rafael, do you know if this new property can be added to the ACPI
> spec, and if so, how to do so? I'm happy to initiate a process if
> someone can point me to, I just hope that publishing a new property to
> the ACPI does not have to block this patch.
> 
> The other option I was thinking of was to use the same property name
> (say "untrusted-device") for both ACPI and device tree platforms, and
> document it in Documentation/devicetree/bindings/pci/pci.txt along
> with others. Since there are other properties there that seem to be
> used similarly (Mika highlighted some below), perhaps that is an
> acceptable solution?
> 
> I had one last question on the property name itself. I was trying to
> understand why a property might have 2 names i.e. "external-facing"
> for DT and "ExternalFacingPort" in ACPI?

I picked "external-facing" for DT to be consistent with other device tree
property names. There doesn't seem to be any CamelCase in device trees
[1], so we should probably keep that convention for new properties as
well. The internal device_property could use the DT name and the ACPI name
can be different. We do something similar with properties "pasid-num-bits"
and "dma-can-stall" which are extracted from the IORT table in
iort_named_component_init()

Thanks,
Jean

[1] git grep "\<[A-Z][,a-zA-Z0-9]\+ =" -- '*.dts'

> Are there any naming
> convention requirements that require ACPI and DT property names to be
> different? Is "untrusted-device" an acceptable ACPI property name?
> 
> Thanks & Best Regards,
> 
> Rajat