• Lyude Paul's avatar
    drm/nouveau/i2c: Disable i2c bus access after ->fini() · 342406e4
    Lyude Paul authored
    For a while, we've had the problem of i2c bus access not grabbing
    a runtime PM ref when it's being used in userspace by i2c-dev, resulting
    in nouveau spamming the kernel log with errors if anything attempts to
    access the i2c bus while the GPU is in runtime suspend. An example:
    
    [  130.078386] nouveau 0000:01:00.0: i2c: aux 000d: begin idle timeout ffffffff
    
    Since the GPU is in runtime suspend, the MMIO region that the i2c bus is
    on isn't accessible. On x86, the standard behavior for accessing an
    unavailable MMIO region is to just return ~0.
    
    Except, that turned out to be a lie. While computers with a clean
    concious will return ~0 in this scenario, some machines will actually
    completely hang a CPU on certian bad MMIO accesses. This was witnessed
    with someone's Lenovo ThinkPad P50, where sensors-detect attempting to
    access the i2c bus while the GPU was suspended would result in a CPU
    hang:
    
      CPU: 5 PID: 12438 Comm: sensors-detect Not tainted 5.0.0-0.rc4.git3.1.fc30.x86_64 #1
      Hardware name: LENOVO 20EQS64N17/20EQS64N17, BIOS N1EET74W (1.47 ) 11/21/2017
      RIP: 0010:ioread32+0x2b/0x30
      Code: 81 ff ff ff 03 00 77 20 48 81 ff 00 00 01 00 76 05 0f b7 d7 ed c3
      48 c7 c6 e1 0c 36 96 e8 2d ff ff ff b8 ff ff ff ff c3 8b 07 <c3> 0f 1f
      40 00 49 89 f0 48 81 fe ff ff 03 00 76 04 40 88 3e c3 48
      RSP: 0018:ffffaac3c5007b48 EFLAGS: 00000292 ORIG_RAX: ffffffffffffff13
      RAX: 0000000001111000 RBX: 0000000001111000 RCX: 0000043017a97186
      RDX: 0000000000000aaa RSI: 0000000000000005 RDI: ffffaac3c400e4e4
      RBP: ffff9e6443902c00 R08: ffffaac3c400e4e4 R09: ffffaac3c5007be7
      R10: 0000000000000004 R11: 0000000000000001 R12: ffff9e6445dd0000
      R13: 000000000000e4e4 R14: 00000000000003c4 R15: 0000000000000000
      FS:  00007f253155a740(0000) GS:ffff9e644f600000(0000) knlGS:0000000000000000
      CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
      CR2: 00005630d1500358 CR3: 0000000417c44006 CR4: 00000000003606e0
      DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
      DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
      Call Trace:
       g94_i2c_aux_xfer+0x326/0x850 [nouveau]
       nvkm_i2c_aux_i2c_xfer+0x9e/0x140 [nouveau]
       __i2c_transfer+0x14b/0x620
       i2c_smbus_xfer_emulated+0x159/0x680
       ? _raw_spin_unlock_irqrestore+0x1/0x60
       ? rt_mutex_slowlock.constprop.0+0x13d/0x1e0
       ? __lock_is_held+0x59/0xa0
       __i2c_smbus_xfer+0x138/0x5a0
       i2c_smbus_xfer+0x4f/0x80
       i2cdev_ioctl_smbus+0x162/0x2d0 [i2c_dev]
       i2cdev_ioctl+0x1db/0x2c0 [i2c_dev]
       do_vfs_ioctl+0x408/0x750
       ksys_ioctl+0x5e/0x90
       __x64_sys_ioctl+0x16/0x20
       do_syscall_64+0x60/0x1e0
       entry_SYSCALL_64_after_hwframe+0x49/0xbe
      RIP: 0033:0x7f25317f546b
      Code: 0f 1e fa 48 8b 05 1d da 0c 00 64 c7 00 26 00 00 00 48 c7 c0 ff ff
      ff ff c3 66 0f 1f 44 00 00 f3 0f 1e fa b8 10 00 00 00 0f 05 <48> 3d 01
      f0 ff ff 73 01 c3 48 8b 0d ed d9 0c 00 f7 d8 64 89 01 48
      RSP: 002b:00007ffc88caab68 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
      RAX: ffffffffffffffda RBX: 00005630d0fe7260 RCX: 00007f25317f546b
      RDX: 00005630d1598e80 RSI: 0000000000000720 RDI: 0000000000000003
      RBP: 00005630d155b968 R08: 0000000000000001 R09: 00005630d15a1da0
      R10: 0000000000000070 R11: 0000000000000246 R12: 00005630d1598e80
      R13: 00005630d12f3d28 R14: 0000000000000720 R15: 00005630d12f3ce0
      watchdog: BUG: soft lockup - CPU#5 stuck for 23s! [sensors-detect:12438]
    
    Yikes! While I wanted to try to make it so that accessing an i2c bus on
    nouveau would wake up the GPU as needed, airlied pointed out that pretty
    much any usecase for userspace accessing an i2c bus on a GPU (mainly for
    the DDC brightness control that some displays have) is going to only be
    useful while there's at least one display enabled on the GPU anyway, and
    the GPU never sleeps while there's displays running.
    
    Since teaching the i2c bus to wake up the GPU on userspace accesses is a
    good deal more difficult than it might seem, mostly due to the fact that
    we have to use the i2c bus during runtime resume of the GPU, we instead
    opt for the easiest solution: don't let userspace access i2c busses on
    the GPU at all while it's in runtime suspend.
    
    Changes since v1:
    * Also disable i2c busses that run over DP AUX
    Signed-off-by: default avatarLyude Paul <lyude@redhat.com>
    Cc: stable@vger.kernel.org
    Signed-off-by: default avatarBen Skeggs <bskeggs@redhat.com>
    342406e4
aux.c 4.69 KB