While I had thought I had fixed this issue in:
commit 342406e4fb ("drm/nouveau/i2c: Disable i2c bus access after
->fini()")
It turns out that while I did fix the error messages I was seeing on my
P50 when trying to access i2c busses with the GPU in runtime suspend, I
accidentally had missed one important detail that was mentioned on the
bug report this commit was supposed to fix: that the CPU would only lock
up when trying to access i2c busses _on connected devices_ _while the
GPU is not in runtime suspend_. Whoops. That definitely explains why I
was not able to get my machine to hang with i2c bus interactions until
now, as plugging my P50 into it's dock with an HDMI monitor connected
allowed me to finally reproduce this locally.
Now that I have managed to reproduce this issue properly, it looks like
the problem is much simpler then it looks. It turns out that some
connected devices, such as MST laptop docks, will actually ACK i2c reads
even if no data was actually read:
[ 275.063043] nouveau 0000:01:00.0: i2c: aux 000a: 1: 0000004c 1
[ 275.063447] nouveau 0000:01:00.0: i2c: aux 000a: 00 01101000 10040000
[ 275.063759] nouveau 0000:01:00.0: i2c: aux 000a: rd 00000001
[ 275.064024] nouveau 0000:01:00.0: i2c: aux 000a: rd 00000000
[ 275.064285] nouveau 0000:01:00.0: i2c: aux 000a: rd 00000000
[ 275.064594] nouveau 0000:01:00.0: i2c: aux 000a: rd 00000000
Because we don't handle the situation of i2c ack without any data, we
end up entering an infinite loop in nvkm_i2c_aux_i2c_xfer() since the
value of cnt always remains at 0. This finally properly explains how
this could result in a CPU hang like the ones observed in the
aforementioned commit.
So, fix this by retrying transactions if no data is written or received,
and give up and fail the transaction if we continue to not write or
receive any data after 32 retries.
Signed-off-by: Lyude Paul <lyude@redhat.com>
Cc: stable@vger.kernel.org
Signed-off-by: Ben Skeggs <bskeggs@redhat.com>
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: Lyude Paul <lyude@redhat.com>
Cc: stable@vger.kernel.org
Signed-off-by: Ben Skeggs <bskeggs@redhat.com>
Since switching the I2C-over-AUX helpers, there have been regressions on
some display combinations due to us not having support for "address only"
transactions.
This commits enables support for them for GF119 and newer.
Earlier GPUs have been reverted to a custom I2C-over-AUX algorithm.
Signed-off-by: Ben Skeggs <bskeggs@redhat.com>
Apparently sinks are allows to respond with ACK even if they didn't
fully complete a transaction... It seems like a missed opportunity
for DEFER to me, but what do I know :)
Signed-off-by: Ben Skeggs <bskeggs@redhat.com>
The namespace of NVKM is being changed to nvkm_ instead of nouveau_,
which will be used for the DRM part of the driver. This is being
done in order to make it very clear as to what part of the driver a
given symbol belongs to, and as a minor step towards splitting the
DRM driver out to be able to stand on its own (for virt).
Because there's already a large amount of churn here anyway, this is
as good a time as any to also switch to NVIDIA's device and chipset
naming to ease collaboration with them.
A comparison of objdump disassemblies proves no code changes.
Signed-off-by: Ben Skeggs <bskeggs@redhat.com>
The symlinks were annoying some people, and they're not used anywhere
else in the kernel tree. The include directory structure has been
changed so that symlinks aren't needed anymore.
NVKM has been moved from core/ to nvkm/ to make it more obvious as to
what the directory is for, and as some minor prep for when NVKM gets
split out into its own module (virt) at a later date.
Signed-off-by: Ben Skeggs <bskeggs@redhat.com>
Lyude Paul