linux-kernel - Re: [PATCH v4] PCI: Relabel JHL6540 on Lenovo X1 Carbon 7,8

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Message-ID: <20240826054103.GO1532424@black.fi.intel.com>
Date: Mon, 26 Aug 2024 08:41:03 +0300
From: Mika Westerberg <mika.westerberg@...ux.intel.com>
To: Lukas Wunner <lukas@...ner.de>
Cc: Esther Shimanovich <eshimanovich@...omium.org>,
	Mario Limonciello <mario.limonciello@....com>,
	Dmitry Torokhov <dmitry.torokhov@...il.com>,
	Bjorn Helgaas <bhelgaas@...gle.com>, linux-pci@...r.kernel.org,
	linux-kernel@...r.kernel.org, Rajat Jain <rajatja@...gle.com>
Subject: Re: [PATCH v4] PCI: Relabel JHL6540 on Lenovo X1 Carbon 7,8

Hi Lukas,

On Sun, Aug 25, 2024 at 04:29:34PM +0200, Lukas Wunner wrote:
> On Mon, Jul 29, 2024 at 11:04:41AM +0300, Mika Westerberg wrote:
> > On Sun, Jul 28, 2024 at 05:41:09PM +0200, Lukas Wunner wrote:
> > > Do the DROMs on ICM root switches generally lack PCIe Upstream and
> > > Downstream Adapter Entries?
> > 
> > My guess is that they are not populated for ICM host router DROM
> > entries. These are pretty much Apple stuff and USB4 dropped them
> > completely in favour of the router operations.
> 
> I note that Microsoft specifies a "usb4-port-number" for PCIe Downstream
> Adapters as well as DP and USB ports:
> 
> https://learn.microsoft.com/en-us/windows-hardware/drivers/pci/dsd-for-pcie-root-ports#mapping-native-protocols-pcie-displayport-tunneled-through-usb4-to-usb4-host-routers
> 
> Presumably the "usb4-port-number" allows for associating a
> pci_dev with a tb_port.  So that's a third way to do that,
> on top of DROM entries and the USB4 router operation.

It matches the "USB4 port" number of the host router.

> What I don't quite understand is whether the "usb4-port-number"
> is only present on PCIe Adapters of the Host Router or whether
> it can also exist on PCIe Adapters of Device Routers?

It is is only present on host router and only for PCIe and USB ports
(I'ven not seen it been used with DisplayPort).

> I would also like to know whether "usb4-port-number" is set on
> the machines that Esther's quirk seeks to fix?

This is only present in USB4 software connection manager systems so not
on any of those as far as I can tell.