Re: [PATCH 0/2] Mark USB4 controllers as is_thunderbolt

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On Mon, Feb 07, 2022 at 03:52:13PM +0000, Deucher, Alexander wrote:
> > From: Mika Westerberg <mika.westerberg@xxxxxxxxxxxxxxx>
> > The other option is to look for ACPI companion (ACPI_COMPANION()) of the
> > device. AFAICT dGPUs don't have one (as the BIOS does not know in advance
> > what will be connected to the hotplug ports) whereas internal does typically
> > have one.
> 
> Yeah, this is probably the right way to do this.

No, that doesn't work.  At least Apple represents the first few devices
in the Thunderbolt daisy-chain in the ACPI namespace, so IIUC you'd find
an ACPI companion for those but not for the remainder of the daisy-chain.
This is from a 2019/2020 MacBookPro16,1:

$ grep 'Device ' acpidump/mbp161/ssdt6.dsl
            Device (UPSB)
                Device (DSB0)
                    Device (NHI0)
                Device (DSB1)
                    Device (UPS0)
                        Device (DSB0)
                            Device (DEV0)
                        Device (DSB3)
                            Device (UPS0)
                                Device (DSB0)
                                    Device (DEV0)
                                Device (DSB3)
                                    Device (DEV0)
            ...

There's a *reason* why I introduced the is_thunderbolt flag,
there is no other reliable way to detect externally attached devices.

Thanks,

Lukas



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