ASPEED graphics card: ast_pci_probe causes RCU stalls

[poza]

Hi,


we have on-board ASPEED Graphics card on PCIe.

kernel version: 4.16

I select following drive to enable ast graphics support.
Symbol: DRM_AST [=y]                                                     
                                                                         
                                                          \u2502
  AST server chips                                                       
                                                                         
                                                    \u2502
  Location:                                                              
                                                                         
                                                          \u2502
  -> Device Drivers                                                      
                                                                         
                                                        \u2502
    -> Graphics support                                                  
                                                                         
                                                        \u2502
  Defined at drivers/gpu/drm/ast/Kconfig:1                               
                                                                         
                                                          \u2502
  Depends on: HAS_IOMEM [=y] && DRM [=y] && PCI [=y] && MMU [=y]         
                                                                         
                                                          \u2502
  Selects: DRM_TTM [=y] && DRM_KMS_HELPER [=y] && DRM_TTM [=y]

lspci -vvv output.
-----------------------------

0007:02:00.0 VGA compatible controller: ASPEED Technology, Inc. ASPEED 
Graphics Family (rev 41) (prog-if 00 [VGA controller])
        Subsystem: ASPEED Technology, Inc. ASPEED Graphics Family
        Control: I/O+ Mem+ BusMaster+ SpecCycle- MemWINV- VGASnoop- 
ParErr- Stepping- SERR- FastB2B- DisINTx-
        Status: Cap+ 66MHz- UDF- FastB2B- ParErr- DEVSEL=medium >TAbort- 
<TAbort- <MAbort- >SERR- <PERR- INTx-
        Latency: 0
        Interrupt: pin A routed to IRQ 255
        Region 0: Memory at e70101000000 (32-bit, non-prefetchable) 
[size=16M]
        Region 1: Memory at e70100800000 (32-bit, non-prefetchable) 
[size=128K]
        Region 2: I/O ports at 60000 [size=128]
        Capabilities: [40] Power Management version 3
                Flags: PMEClk- DSI- D1+ D2+ AuxCurrent=375mA 
PME(D0+,D1+,D2+,D3hot+,D3cold+)
                Status: D0 NoSoftRst- PME-Enable- DSel=0 DScale=0 PME-
        Capabilities: [50] MSI: Enable- Count=1/2 Maskable- 64bit+
                Address: 0000000000000000  Data: 0000


it seems to me that; ast_pci_probe seems to stuck in set_clock

[   38.293239] INFO: rcu_sched self-detected stall on CPU
[   38.300808]  0-....: (35 ticks this GP) 
idle=256/1/4611686018427387906 softirq=183/183 fqs=187
[   38.313653]   (t=421 jiffies g=-232 c=-233 q=322)
[   38.320592] Task dump for CPU 0:
[   38.325566] kworker/0:0     R  running task        0     3      2 
0x00000002
[   38.335989] Workqueue: events work_for_cpu_fn
[   38.342409] Call trace:
[   38.346025]  dump_backtrace+0x0/0x170
[   38.351413]  show_stack+0x14/0x20
[   38.356297]  sched_show_task+0x104/0x128
[   38.362173]  dump_cpu_task+0x40/0x50
[   38.367441]  rcu_dump_cpu_stacks+0x94/0xd4
[   38.373480]  rcu_check_callbacks+0x574/0x7b0
[   38.379785]  update_process_times+0x2c/0x58
[   38.385946]  tick_sched_handle.isra.5+0x30/0x50
[   38.393830]  tick_sched_timer+0x40/0x90
[   38.399480]  __hrtimer_run_queues+0x120/0x1b8
[   38.405895]  hrtimer_interrupt+0xd4/0x250
[   38.411815]  arch_timer_handler_phys+0x28/0x40
[   38.418361]  handle_percpu_devid_irq+0x80/0x138
[   38.425152]  generic_handle_irq+0x24/0x38
[   38.431057]  __handle_domain_irq+0x5c/0xb0
[   38.437104]  gic_handle_irq+0x7c/0x184
[   38.442639]  el1_irq+0xb0/0x140
[   38.447265]  ast_get_index_reg_mask+0x4/0x38
[   38.453553]  __i2c_bit_add_bus+0x54/0x3e0
[   38.459532]  i2c_bit_add_bus+0x14/0x20
[   38.465057]  ast_mode_init+0x230/0x358
[   38.470584]  ast_driver_load+0x5a4/0x968
[   38.476368]  drm_dev_register+0x154/0x1d8
[   38.482283]  drm_get_pci_dev+0x94/0x160
[   38.488047]  ast_pci_probe+0x18/0x20
[   38.493318]  local_pci_probe+0x28/0x80
[   38.498830]  work_for_cpu_fn+0x18/0x28
[   38.504367]  process_one_work+0x1d4/0x310
[   38.510271]  worker_thread+0x230/0x470
[   38.515804]  kthread+0x128/0x130
[   38.520777]  ret_from_fork+0x10/0x18

Regards,
Oza.