Hi, On Mon, Feb 07, 2022 at 03:00:19PM +0000, Deucher, Alexander wrote: > [Public] > > > -----Original Message----- > > From: Mika Westerberg <mika.westerberg@xxxxxxxxxxxxxxx> > > Sent: Monday, February 7, 2022 1:42 AM > > To: Limonciello, Mario <Mario.Limonciello@xxxxxxx> > > Cc: Bjorn Helgaas <bhelgaas@xxxxxxxxxx>; Andreas Noever > > <andreas.noever@xxxxxxxxx>; open list:PCI SUBSYSTEM <linux- > > pci@xxxxxxxxxxxxxxx>; open list:THUNDERBOLT DRIVER <linux- > > usb@xxxxxxxxxxxxxxx>; Michael Jamet <michael.jamet@xxxxxxxxx>; Yehezkel > > Bernat <YehezkelShB@xxxxxxxxx>; Deucher, Alexander > > <Alexander.Deucher@xxxxxxx> > > Subject: Re: [PATCH 0/2] Mark USB4 controllers as is_thunderbolt > > > > Hi Mario, > > > > On Fri, Feb 04, 2022 at 12:28:18PM -0600, Mario Limonciello wrote: > > > Various drivers in the kernel use `pci_is_thunderbolt_attached` to > > > designate behaving differently from a device that is internally in the > > > machine. This function relies upon the `is_thunderbolt` designation > > > which checks for a specific capability only set on Intel controllers. > > > > > > Non-Intel USB4 designs should also match this designation so that they > > > can be treated the same regardless of the host they're connected to. > > > > Not objecting this if really needed but since USB4 is supposed to be > > transparent to the native (tunneled) protocol, I would rather try to figure out > > if there is really need to change driver behaviour whether it is connected > > over USB4 or plugged natively on the PCIe slot. > > > > Can you elaborate a bit what kind of functionality needs this? Perhaps we can > > figure a better alternative? > > In the AMD GPU driver we use it to determine which dGPU is built into > a platform vs. externally connected since the internal one uses ACPI > for certain things and the external one does not. There are probably > other ways to determine this, but it's not in place at the moment. Can't you check if the device is behind a hotplug bridge? Then for certain it is "removable". 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.
