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References: <20190409202335.4190-1-lyude@redhat.com>
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From:   Ben Skeggs <skeggsb@gmail.com>
Date:   Thu, 11 Apr 2019 08:48:26 +1000
Message-ID: <CACAvsv5woW9wr3JaKSOSSX8v4NACv5ubVyCoO9q9+OumspwsZQ@mail.gmail.com>
Subject: Re: [PATCH v2] drm/nouveau/i2c: Disable i2c bus access after ->fini()
To:     Lyude Paul <lyude@redhat.com>
Cc:     nouveau@lists.freedesktop.org, David Airlie <airlied@linux.ie>,
        linux-kernel@vger.kernel.org, dri-devel@lists.freedesktop.org,
        Ben Skeggs <bskeggs@redhat.com>, stable@vger.kernel.org
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On Wed, 10 Apr 2019 at 06:23, Lyude Paul <lyude@redhat.com> wrote:
>
> 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
I've updated my tree with the v2 version of the patch.  I haven't
investigated too thoroughly, but shouldn't it be possible to move this
check into a single place (pad_acquire()?) for both i2c/aux?

Thanks,
Ben.

>
> Signed-off-by: Lyude Paul <lyude@redhat.com>
> Cc: stable@vger.kernel.org
> ---
>  .../gpu/drm/nouveau/include/nvkm/subdev/i2c.h |  2 ++
>  drivers/gpu/drm/nouveau/nvkm/subdev/i2c/aux.c | 26 ++++++++++++++++++-
>  drivers/gpu/drm/nouveau/nvkm/subdev/i2c/aux.h |  2 ++
>  .../gpu/drm/nouveau/nvkm/subdev/i2c/base.c    | 15 +++++++++++
>  drivers/gpu/drm/nouveau/nvkm/subdev/i2c/bus.c | 21 ++++++++++++++-
>  drivers/gpu/drm/nouveau/nvkm/subdev/i2c/bus.h |  1 +
>  6 files changed, 65 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/gpu/drm/nouveau/include/nvkm/subdev/i2c.h b/drivers/gpu/drm/nouveau/include/nvkm/subdev/i2c.h
> index eef54e9b5d77..7957eafa5f0e 100644
> --- a/drivers/gpu/drm/nouveau/include/nvkm/subdev/i2c.h
> +++ b/drivers/gpu/drm/nouveau/include/nvkm/subdev/i2c.h
> @@ -38,6 +38,7 @@ struct nvkm_i2c_bus {
>         struct mutex mutex;
>         struct list_head head;
>         struct i2c_adapter i2c;
> +       u8 enabled;
>  };
>
>  int nvkm_i2c_bus_acquire(struct nvkm_i2c_bus *);
> @@ -57,6 +58,7 @@ struct nvkm_i2c_aux {
>         struct mutex mutex;
>         struct list_head head;
>         struct i2c_adapter i2c;
> +       u8 enabled;
>
>         u32 intr;
>  };
> diff --git a/drivers/gpu/drm/nouveau/nvkm/subdev/i2c/aux.c b/drivers/gpu/drm/nouveau/nvkm/subdev/i2c/aux.c
> index 4c1f547da463..b4e7404fe660 100644
> --- a/drivers/gpu/drm/nouveau/nvkm/subdev/i2c/aux.c
> +++ b/drivers/gpu/drm/nouveau/nvkm/subdev/i2c/aux.c
> @@ -105,9 +105,15 @@ nvkm_i2c_aux_acquire(struct nvkm_i2c_aux *aux)
>  {
>         struct nvkm_i2c_pad *pad = aux->pad;
>         int ret;
> +
>         AUX_TRACE(aux, "acquire");
>         mutex_lock(&aux->mutex);
> -       ret = nvkm_i2c_pad_acquire(pad, NVKM_I2C_PAD_AUX);
> +
> +       if (aux->enabled)
> +               ret = nvkm_i2c_pad_acquire(pad, NVKM_I2C_PAD_AUX);
> +       else
> +               ret = -EIO;
> +
>         if (ret)
>                 mutex_unlock(&aux->mutex);
>         return ret;
> @@ -145,6 +151,24 @@ nvkm_i2c_aux_del(struct nvkm_i2c_aux **paux)
>         }
>  }
>
> +void
> +nvkm_i2c_aux_init(struct nvkm_i2c_aux *aux)
> +{
> +       AUX_TRACE(aux, "init");
> +       mutex_lock(&aux->mutex);
> +       aux->enabled = true;
> +       mutex_unlock(&aux->mutex);
> +}
> +
> +void
> +nvkm_i2c_aux_fini(struct nvkm_i2c_aux *aux)
> +{
> +       AUX_TRACE(aux, "fini");
> +       mutex_lock(&aux->mutex);
> +       aux->enabled = false;
> +       mutex_unlock(&aux->mutex);
> +}
> +
>  int
>  nvkm_i2c_aux_ctor(const struct nvkm_i2c_aux_func *func,
>                   struct nvkm_i2c_pad *pad, int id,
> diff --git a/drivers/gpu/drm/nouveau/nvkm/subdev/i2c/aux.h b/drivers/gpu/drm/nouveau/nvkm/subdev/i2c/aux.h
> index 7d56c4ba693c..08f6b2ee64ab 100644
> --- a/drivers/gpu/drm/nouveau/nvkm/subdev/i2c/aux.h
> +++ b/drivers/gpu/drm/nouveau/nvkm/subdev/i2c/aux.h
> @@ -16,6 +16,8 @@ int nvkm_i2c_aux_ctor(const struct nvkm_i2c_aux_func *, struct nvkm_i2c_pad *,
>  int nvkm_i2c_aux_new_(const struct nvkm_i2c_aux_func *, struct nvkm_i2c_pad *,
>                       int id, struct nvkm_i2c_aux **);
>  void nvkm_i2c_aux_del(struct nvkm_i2c_aux **);
> +void nvkm_i2c_aux_init(struct nvkm_i2c_aux *);
> +void nvkm_i2c_aux_fini(struct nvkm_i2c_aux *);
>  int nvkm_i2c_aux_xfer(struct nvkm_i2c_aux *, bool retry, u8 type,
>                       u32 addr, u8 *data, u8 *size);
>
> diff --git a/drivers/gpu/drm/nouveau/nvkm/subdev/i2c/base.c b/drivers/gpu/drm/nouveau/nvkm/subdev/i2c/base.c
> index 4f197b15acf6..ecacb22834d7 100644
> --- a/drivers/gpu/drm/nouveau/nvkm/subdev/i2c/base.c
> +++ b/drivers/gpu/drm/nouveau/nvkm/subdev/i2c/base.c
> @@ -160,8 +160,18 @@ 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;
> +       struct nvkm_i2c_aux *aux;
>         u32 mask;
>
> +       list_for_each_entry(aux, &i2c->aux, head) {
> +               nvkm_i2c_aux_fini(aux);
> +       }
> +
> +       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);
> @@ -180,6 +190,7 @@ nvkm_i2c_init(struct nvkm_subdev *subdev)
>         struct nvkm_i2c *i2c = nvkm_i2c(subdev);
>         struct nvkm_i2c_bus *bus;
>         struct nvkm_i2c_pad *pad;
> +       struct nvkm_i2c_aux *aux;
>
>         list_for_each_entry(pad, &i2c->pad, head) {
>                 nvkm_i2c_pad_init(pad);
> @@ -189,6 +200,10 @@ nvkm_i2c_init(struct nvkm_subdev *subdev)
>                 nvkm_i2c_bus_init(bus);
>         }
>
> +       list_for_each_entry(aux, &i2c->aux, head) {
> +               nvkm_i2c_aux_init(aux);
> +       }
> +
>         return 0;
>  }
>
> 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);
>
> --
> 2.20.1
>
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