[BUG] Apple Mac mini 2018 + Thunderbolt 3 eGPU: PCI bridge window / BAR allocation failure prevents NVIDIA and AMD GPUs from initializing

[BUG] Apple Mac mini 2018 + Thunderbolt 3 eGPU: PCI bridge window / BAR allocation failure prevents NVIDIA and AMD GPUs from initializing

[Michal Babička]

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Hello,

I am reporting a reproducible PCI resource allocation problem on an
Apple Mac mini 2018 with a Thunderbolt 3 eGPU enclosure.

Hardware:

Apple Mac mini 2018
Razer Core X Chroma
NVIDIA GPU tested
AMD Radeon Vega 64 tested
Zorin OS 18 Pro
kernels tested: 6.12.x and 6.17.x

Problem summary:
The eGPU enclosure and GPU are detected and enumerated on the PCI bus,
but GPU initialization fails because PCI bridge windows / BAR
resources are not assigned correctly.

This reproduces with multiple GPU vendors in the same enclosure on the
same host, which suggests a PCI / Thunderbolt bridge resource
allocation problem on this platform rather than a vendor-specific
driver issue.

Expected behavior:
The kernel should assign valid PCI bridge windows and BAR resources so
the GPU can initialize successfully and become usable.

Actual behavior:
The GPU is visible on the PCI bus, but bridge windows and BAR
resources are incomplete or invalid, leaving the device unusable.

Observed errors include:

bridge window [mem size ...]: can't assign; no space
NVRM: BAR1 is 0M @ 0x0
RmInitAdapter failed
NVIDIA initialization fails
AMD shows similar behavior in the same enclosure on the same host

Kernel command line used for the latest debug boot:
BOOT_IMAGE=/boot/vmlinuz-6.17.0-19-generic
root=UUID=f0048c61-b4fe-4edb-9af5-bc756f9e2e7d ro quiet splash
"dyndbg=file drivers/pci/* +p" vt.handoff=7

I also confirmed that dynamic debug for drivers/pci was enabled.

I collected and attached two archives:

egpu-logs.tar.gz
egpu-logs-dyndbg.tar.gz

These archives contain:

full dmesg
dmesg extract
lspci -nnvvv
lspci tree
per-device lspci dumps for the relevant bridges and GPU
/proc/iomem
journalctl -b
nvidia-smi output

Please let me know which specific logs or excerpts would be most useful.

Best regards,
Michal Babička

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Re: [WARNING: UNSCANNABLE EXTRACTION FAILED][BUG] Apple Mac mini 2018 + Thunderbolt 3 eGPU: PCI bridge window / BAR allocation failure prevents NVIDIA and AMD GPUs from initializing

[Ilpo Järvinen]

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On Tue, 24 Mar 2026, Michal Babička wrote:

> Hello,
> 
> I am reporting a reproducible PCI resource allocation problem on an
> Apple Mac mini 2018 with a Thunderbolt 3 eGPU enclosure.
> 
> Hardware:
> 
> Apple Mac mini 2018
> Razer Core X Chroma
> NVIDIA GPU tested
> AMD Radeon Vega 64 tested
> Zorin OS 18 Pro
> kernels tested: 6.12.x and 6.17.x
> 
> Problem summary:
> The eGPU enclosure and GPU are detected and enumerated on the PCI bus,
> but GPU initialization fails because PCI bridge windows / BAR
> resources are not assigned correctly.
> 
> This reproduces with multiple GPU vendors in the same enclosure on the
> same host, which suggests a PCI / Thunderbolt bridge resource
> allocation problem on this platform rather than a vendor-specific
> driver issue.
> 
> Expected behavior:
> The kernel should assign valid PCI bridge windows and BAR resources so
> the GPU can initialize successfully and become usable.
> 
> Actual behavior:
> The GPU is visible on the PCI bus, but bridge windows and BAR
> resources are incomplete or invalid, leaving the device unusable.
> 
> Observed errors include:
> 
> bridge window [mem size ...]: can't assign; no space
> NVRM: BAR1 is 0M @ 0x0
> RmInitAdapter failed
> NVIDIA initialization fails
> AMD shows similar behavior in the same enclosure on the same host
> 
> Kernel command line used for the latest debug boot:
> BOOT_IMAGE=/boot/vmlinuz-6.17.0-19-generic
> root=UUID=f0048c61-b4fe-4edb-9af5-bc756f9e2e7d ro quiet splash
> "dyndbg=file drivers/pci/* +p" vt.handoff=7
> 
> I also confirmed that dynamic debug for drivers/pci was enabled.
> 
> I collected and attached two archives:
> 
> egpu-logs.tar.gz
> egpu-logs-dyndbg.tar.gz
> 
> These archives contain:
> 
> full dmesg
> dmesg extract
> lspci -nnvvv
> lspci tree
> per-device lspci dumps for the relevant bridges and GPU
> /proc/iomem
> journalctl -b
> nvidia-smi output
> 
> Please let me know which specific logs or excerpts would be most useful.

Did you have any logs with pci=realloc. There are those claiming conflicts 
resulting in clipping bridge windows from their original size so I'm 
skeptical this case will work well without kernel rearranging the bridge 
windows.

-- 
 i.