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.

Signed-off-by: Lyude Paul lyude@redhat.com Cc: stable@vger.kernel.org --- .../gpu/drm/nouveau/include/nvkm/subdev/i2c.h | 1 + .../gpu/drm/nouveau/nvkm/subdev/i2c/base.c | 5 +++++ drivers/gpu/drm/nouveau/nvkm/subdev/i2c/bus.c | 21 ++++++++++++++++++- drivers/gpu/drm/nouveau/nvkm/subdev/i2c/bus.h | 1 + 4 files changed, 27 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/nouveau/include/nvkm/subdev/i2c.h b/drivers/gpu/drm/nouveau/include/nvkm/subdev/i2c.h index eef54e9b5d77..7c45056c47dd 100644 --- a/drivers/gpu/drm/nouveau/include/nvkm/subdev/i2c.h +++ b/drivers/gpu/drm/nouveau/include/nvkm/subdev/i2c.h @@ -36,6 +36,7 @@ struct nvkm_i2c_bus { int id;

struct mutex mutex; + u8 enabled; struct list_head head; struct i2c_adapter i2c; }; diff --git a/drivers/gpu/drm/nouveau/nvkm/subdev/i2c/base.c b/drivers/gpu/drm/nouveau/nvkm/subdev/i2c/base.c index 4f197b15acf6..54d9882f9931 100644 --- a/drivers/gpu/drm/nouveau/nvkm/subdev/i2c/base.c +++ b/drivers/gpu/drm/nouveau/nvkm/subdev/i2c/base.c @@ -160,8 +160,13 @@ nvkm_i2c_fini(struct nvkm_subdev *subdev, bool suspend) { struct nvkm_i2c *i2c = nvkm_i2c(subdev); struct nvkm_i2c_pad *pad; + struct nvkm_i2c_bus *bus; u32 mask;

+ list_for_each_entry(bus, &i2c->bus, head) { + nvkm_i2c_bus_fini(bus); + } + if ((mask = (1 << i2c->func->aux) - 1), i2c->func->aux_stat) { i2c->func->aux_mask(i2c, NVKM_I2C_ANY, mask, 0); i2c->func->aux_stat(i2c, &mask, &mask, &mask, &mask); diff --git a/drivers/gpu/drm/nouveau/nvkm/subdev/i2c/bus.c b/drivers/gpu/drm/nouveau/nvkm/subdev/i2c/bus.c index 807a2b67bd64..ed50cc3736b9 100644 --- a/drivers/gpu/drm/nouveau/nvkm/subdev/i2c/bus.c +++ b/drivers/gpu/drm/nouveau/nvkm/subdev/i2c/bus.c @@ -110,6 +110,19 @@ nvkm_i2c_bus_init(struct nvkm_i2c_bus *bus) BUS_TRACE(bus, "init"); if (bus->func->init) bus->func->init(bus); + + mutex_lock(&bus->mutex); + bus->enabled = true; + mutex_unlock(&bus->mutex); +} + +void +nvkm_i2c_bus_fini(struct nvkm_i2c_bus *bus) +{ + BUS_TRACE(bus, "fini"); + mutex_lock(&bus->mutex); + bus->enabled = false; + mutex_unlock(&bus->mutex); }

void @@ -126,9 +139,15 @@ nvkm_i2c_bus_acquire(struct nvkm_i2c_bus *bus) { struct nvkm_i2c_pad *pad = bus->pad; int ret; + BUS_TRACE(bus, "acquire"); mutex_lock(&bus->mutex); - ret = nvkm_i2c_pad_acquire(pad, NVKM_I2C_PAD_I2C); + + if (bus->enabled) + ret = nvkm_i2c_pad_acquire(pad, NVKM_I2C_PAD_I2C); + else + ret = -EIO; + if (ret) mutex_unlock(&bus->mutex); return ret; diff --git a/drivers/gpu/drm/nouveau/nvkm/subdev/i2c/bus.h b/drivers/gpu/drm/nouveau/nvkm/subdev/i2c/bus.h index bea0dd33961e..465464bba58b 100644 --- a/drivers/gpu/drm/nouveau/nvkm/subdev/i2c/bus.h +++ b/drivers/gpu/drm/nouveau/nvkm/subdev/i2c/bus.h @@ -18,6 +18,7 @@ int nvkm_i2c_bus_new_(const struct nvkm_i2c_bus_func *, struct nvkm_i2c_pad *, int id, struct nvkm_i2c_bus **); void nvkm_i2c_bus_del(struct nvkm_i2c_bus **); void nvkm_i2c_bus_init(struct nvkm_i2c_bus *); +void nvkm_i2c_bus_fini(struct nvkm_i2c_bus *);

int nvkm_i2c_bit_xfer(struct nvkm_i2c_bus *, struct i2c_msg *, int);