## Summary

Booting the `linux-omarchy` kernel (7.2.5-3) on a 2015 MacBook Pro gives a black
screen: the graphical session starts and then the Radeon dGPU wedges. The Arch
`linux` kernel (7.2.3-arch1-3) on the same machine works fine.

The difference is a kernel config change in the Omarchy kernel:

```
CONFIG_INTEL_IOMMU_DEFAULT_ON=y      # linux-omarchy 7.2.5-3
# CONFIG_INTEL_IOMMU_DEFAULT_ON is not set   # linux 7.2.3-arch1-3
```

Enabling VT-d DMA translation exposes an amdgpu problem on this hardware: the
GPU takes IOMMU faults, its `gfx` ring times out, GPU recovery fails, and the
panel (which is muxed to the dGPU) stays black.

Adding `intel_iommu=off` to the kernel cmdline fixes it.

## Environment

- Omarchy 4.0.4
- Failing kernel: `linux-omarchy` 7.2.5-3 (`7.2.5-3-omarchy`), installed 2026-09-18
- Working kernel: `linux` 7.2.3.arch1-3 (`7.2.3-arch1-3`)
- Hardware: Apple MacBookPro11,5 (MacBook Pro Retina, 15-inch, Mid 2015), i7-4870HQ
  - iGPU: Intel Crystal Well `[8086:0d26]` — `i915`
  - dGPU: AMD Venus XT `[1002:6821]` / Radeon R9 M370X `[106b:0149]` — `amdgpu`
    (VERDE, `gfx_v6_0`, Southern Islands)
  - Internal panel `card1-eDP-1` is driven by the dGPU; `i915` reports
    `failed to retrieve link info, disabling eDP`
- Firmware: Apple UEFI, Secure Boot off; Apple DMAR table present; host address width 39

## Steps to reproduce

1. Install `linux-omarchy` and boot its UKI (`omarchy_linux-omarchy.efi`).
2. It reaches the graphical session and then goes black. Every attempt died within
   1–45 s; the `linux` 7.2.3 entry boots normally.

## Evidence

With `linux-omarchy` the kernel turns IOMMU DMA translation on and creates 27
IOMMU groups:

```
iommu: Default domain type: Translated
DMAR: Intel(R) Virtualization Technology for Directed I/O
pci 0000:00:02.0: Adding to iommu group 0
...
```

The AMD GPU then faults, the ring times out, and recovery fails:

```
DMAR: DRHD: handling fault status reg 3
DMAR: [DMA Read NO_PASID] Request device [0000:01:00.0] fault addr 0x77a00000 [fault reason 0x0c] non-zero reserved fields in PTE
...
amdgpu 0000:01:00.0: ring gfx timeout, signaled seq=2, emitted seq=4
amdgpu 0000:01:00.0:  Process Hyprland pid 1457 thread Hyprland:cs0 pid 1488
amdgpu 0000:01:00.0: GPU reset begin!. Source:  1
amdgpu 0000:01:00.0: GPU reset succeeded, trying to resume
amdgpu 0000:01:00.0: [drm:amdgpu_ring_test_helper [amdgpu]] *ERROR* ring gfx test failed (-110)
amdgpu 0000:01:00.0: resume of IP block <gfx_v6_0> failed -110
amdgpu 0000:01:00.0: GPU reset end with ret = -110
amdgpu 0000:01:00.0: GPU Recovery Failed: -110
```

The address in the second fault is the GPU's GART table
(`PCIE GART of 1024M enabled (table at 0x0000000001400000)`).

Checks comparing the two kernels' boot logs:

| | linux-omarchy 7.2.5 | linux 7.2.3 |
|---|---|---|
| `Adding to iommu group` | 27 | 0 |
| "Virtualization Technology for Directed I/O" | yes | no |
| `DRHD: handling fault` | yes | none |
| `ring gfx timeout` / `GPU Recovery Failed` | yes | none |

The only difference in the IOMMU/DMAR/IOVA category of the two kernel configs is:

```diff
--- linux 7.2.3-arch1-3/.config
+++ linux-omarchy 7.2.5-3/.config
-# CONFIG_INTEL_IOMMU_DEFAULT_ON is not set
+CONFIG_INTEL_IOMMU_DEFAULT_ON=y
```

## Workaround (verified)

Add `intel_iommu=off` to the `linux-omarchy` cmdline and rebuild:

```
# /etc/default/limine
KERNEL_CMDLINE[linux-omarchy]+=" intel_iommu=off"

sudo limine-update
```

After rebooting the Omarchy kernel:

```
/proc/cmdline contains intel_iommu=off
iommu groups: 0
VT-d enabled msg: 0
DMAR faults: 0
ring gfx timeout: 0
GPU Recovery Failed: 0
amdgpu initializes cleanly, amdgpudrmfb owns fb0, eDP-1 connected
```

(`iommu=pt` is another possible workaround, but it wasn't tested here.)

## Suggested fix

- Reconsider defaulting `CONFIG_INTEL_IOMMU_DEFAULT_ON=y` in the Omarchy kernel,
  or scope it so Apple hardware with a muxed AMD dGPU isn't broken by default.
- Alternatively, document/script the `intel_iommu=off` (or `iommu=pt`)
  workaround for this hardware.

I'm happy to test patches/proposed configs on this machine.