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Date:   Fri, 18 Mar 2022 16:10:35 +0100
From:   Lukas Wunner <lukas@wunner.de>
To:     Robin Murphy <robin.murphy@arm.com>
Cc:     "mika.westerberg@linux.intel.com" <mika.westerberg@linux.intel.com>,
        "Limonciello, Mario" <Mario.Limonciello@amd.com>,
        "andreas.noever@gmail.com" <andreas.noever@gmail.com>,
        "michael.jamet@intel.com" <michael.jamet@intel.com>,
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        "linux-usb@vger.kernel.org" <linux-usb@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "iommu@lists.linux-foundation.org" <iommu@lists.linux-foundation.org>,
        "linux-pci@vger.kernel.org" <linux-pci@vger.kernel.org>
Subject: Re: [PATCH] thunderbolt: Make iommu_dma_protection more accurate
Message-ID: <20220318151035.GB11127@wunner.de>
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On Fri, Mar 18, 2022 at 03:51:21PM +0100, Lukas Wunner wrote:
> On Fri, Mar 18, 2022 at 02:08:16PM +0000, Robin Murphy wrote:
> > OK, so do we have any realistic options for identifying the correct PCI
> > devices, if USB4 PCIe adapters might be anywhere relative to their
> > associated NHI? Short of maintaining a list of known IDs, the only thought I
> > have left is that if we walk the whole PCI segment looking specifically for
> > hotplug-capable Gen1 ports, any system modern enough to have Thunderbolt is
> > *probably* not going to have any real PCIe Gen1 hotplug slots, so maybe
> > false negatives might be tolerable, but it still feels like a bit of a
> > sketchy heuristic.
> 
> The Thunderbolt Device ROM contains the PCI slot number, so you can
> correlate the Thunderbolt switch ports with PCIe downstream ports
> and know exactly where PCIe tunnels are terminated.
[...]
> I implemented that in 2018, so it won't apply cleanly to current
> mainline.  But I kept forward-porting it on my private branch and
> could push that to GitHub if anyone is interested.

FWIW, here's the most recent forward-port I've done:

https://github.com/l1k/linux/commits/thunderbolt_correlate_5.13