Hello Rafael, Bjorn, Mika, Dmitry, Greg, Thanks a lot for your comments. On Tue, Jan 25, 2022 at 6:45 AM Rafael J. Wysocki <rafael@xxxxxxxxxx> wrote: > > On Tue, Jan 25, 2022 at 1:55 PM Mika Westerberg > <mika.westerberg@xxxxxxxxxxxxxxx> wrote: > > > > On Tue, Jan 25, 2022 at 12:15:02PM +0100, Greg Kroah-Hartman wrote: > > > On Tue, Jan 25, 2022 at 12:58:52PM +0200, Mika Westerberg wrote: > > > > On Mon, Jan 24, 2022 at 08:27:17AM +0200, Mika Westerberg wrote: > > > > > > > This patch introduces a new "UntrustedDevice" property that can be used > > > > > > > by the firmware to mark any device as untrusted. > > > > > > > > > > I think this new property should be documented somewhere too (also > > > > > explain when to use it instead of ExternalFacingPort). If not in the > > > > > next ACPI spec or some supplemental doc then perhaps in the DT bindings > > > > > under Documentation/devicetree/bindings. > > > > > > > > Actually Microsoft has similar already: > > > > > > > > https://docs.microsoft.com/en-us/windows-hardware/drivers/pci/dsd-for-pcie-root-ports#identifying-internal-pcie-ports-accessible-to-users-and-requiring-dma-protection > > > > > > > > I think we should use that too here. But because this property also applies to a root port (only), it only helps if the device is downstream a PCIe root port. In our case, we have an internal (wifi) device 00:14.3 (sits on the internal PCI bus 0), so cannot use this. > > > > > > But we do not have "dma protection" for Linux, so how will that value > > > make sense? > > > > Yes I think we do - IOMMU. That's the same thing what we do now for > > "External Facing Ports". This one just is for internal ones. > > > > > 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? 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 > > > > Some of these that we use in Linux too are from that same page: > > > > https://docs.microsoft.com/en-us/windows-hardware/drivers/pci/dsd-for-pcie-root-ports > > > > Namely these: HotPlugSupportInD3, ExternalFacingPort, usb4-host-interface, > > usb4-port-number and StorageD3Enable. > > Right. > > We are kind of on the receiving end here, because at the time we learn > about these things the decisions to use them have been made already.
