[REGRESSION] drm/radeon: Don't register Thunderbolt eGPU with vga_switcheroo

[Nicolai Stange <nicstange@gmail.com>]

Hi,

I'm experiencing a boot failure on next-20170515:

  BUG: unable to handle kernel NULL pointer dereference at 00000000000007cb
  IP: radeon_driver_load_kms+0xeb/0x230 [radeon]
  PGD 0 
  P4D 0 
  
  Oops: 0000 [#1] SMP
  Modules linked in: amdkfd amd_iommu_v2 i915(+) radeon(+) i2c_algo_bit drm_kms_helper ttm e1000e drm sdhci_pci sdhci_acpi ptp sdhci crc32c_intel serio_raw mmc_core pps_core video i2c_hid hid_plantronics
  CPU: 4 PID: 389 Comm: systemd-udevd Not tainted 4.12.0-rc1-next-20170515+ #1
  Hardware name: Dell Inc. Latitude E6540/0725FP, BIOS A10 06/26/2014
  task: ffff97d62c8f0000 task.stack: ffffb96f01478000
  RIP: 0010:radeon_driver_load_kms+0xeb/0x230 [radeon]
  RSP: 0018:ffffb96f0147b9d0 EFLAGS: 00010246
  RAX: 0000000000000000 RBX: ffff97d620085000 RCX: 0000000000610037
  RDX: 0000000000000000 RSI: 000000000000002b RDI: 0000000000000000
  RBP: ffffb96f0147b9e8 R08: 0000000000000002 R09: ffffb96f0147b924
  R10: 0000000000000000 R11: ffff97d62edd2ec0 R12: ffff97d628d5c000
  R13: 0000000000610037 R14: ffffffffc0698280 R15: 0000000000000000
  FS:  00007f496363d8c0(0000) GS:ffff97d62eb00000(0000) knlGS:0000000000000000
  CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
  CR2: 00000000000007cb CR3: 000000022c14c000 CR4: 00000000001406e0
  Call Trace:
   drm_dev_register+0x146/0x1d0 [drm]
   drm_get_pci_dev+0x9a/0x180 [drm]
   radeon_pci_probe+0xb8/0xe0 [radeon]
   local_pci_probe+0x45/0xa0
   pci_device_probe+0x14f/0x1a0
   driver_probe_device+0x29c/0x450
   __driver_attach+0xdf/0xf0
   ? driver_probe_device+0x450/0x450
   bus_for_each_dev+0x6c/0xc0
   driver_attach+0x1e/0x20
   bus_add_driver+0x170/0x270
   driver_register+0x60/0xe0
   ? 0xffffffffc0508000
   __pci_register_driver+0x4c/0x50
   drm_pci_init+0xeb/0x100 [drm]
   ? vga_switcheroo_register_handler+0x6a/0x90
   ? 0xffffffffc0508000
   radeon_init+0x98/0xb6 [radeon]
   do_one_initcall+0x52/0x1a0
   ? __vunmap+0x81/0xb0
   ? kmem_cache_alloc_trace+0x159/0x1b0
   ? do_init_module+0x27/0x1f8
   do_init_module+0x5f/0x1f8
   load_module+0x27ce/0x2be0
   SYSC_finit_module+0xdf/0x110
   ? SYSC_finit_module+0xdf/0x110
   SyS_finit_module+0xe/0x10
   do_syscall_64+0x67/0x150
   entry_SYSCALL64_slow_path+0x25/0x25
  RIP: 0033:0x7f4962295679
  RSP: 002b:00007ffdd8c4f878 EFLAGS: 00000246 ORIG_RAX: 0000000000000139
  RAX: ffffffffffffffda RBX: 000055c014ed8200 RCX: 00007f4962295679
  RDX: 0000000000000000 RSI: 00007f4962dd19c5 RDI: 0000000000000010
  RBP: 00007f4962dd19c5 R08: 0000000000000000 R09: 00007ffdd8c4f990
  R10: 0000000000000010 R11: 0000000000000246 R12: 0000000000000000
  R13: 000055c014ed81a0 R14: 0000000000020000 R15: 000055c0149d1fca
  Code: 5d 5d c3 8b 05 a7 05 14 00 49 81 cd 00 00 08 00 85 c0 74 a3 e8 e7 c0 0e 00 84 c0 74 9a 41 f7 c5 00 00 02 00 75 91 49 8b 44 24 10 <0f> b6 90 cb 07 00 00 f6 c2 20 74 1e e9 7b ff ff ff 48 8b 40 38 
  RIP: radeon_driver_load_kms+0xeb/0x230 [radeon] RSP: ffffb96f0147b9d0
  CR2: 00000000000007cb
  ---[ end trace 89cc4ba7e569c65c ]---


Bisection lead to commit 7ffb0ce31cf9 ("drm/radeon: Don't register
Thunderbolt eGPU with vga_switcheroo"). Reverting this commit on top of
next-20170515 fixes the issue for me.

My box is a Dell laptop which most certainly hasn't got any Thunderbolt
circuitry.

lspci says that my radeon card is a
  01:00.0 VGA compatible controller: Advanced Micro Devices, Inc. [AMD/ATI] Mars XTX [Radeon HD 8790M] (rev ff) (prog-if ff)

or in raw form:

  01:00.0 0300: 1002:6606 (rev ff)


Thanks,

Nicolai
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