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Date:   Thu, 11 Apr 2019 13:37:16 -0400
From:   Lyude Paul <lyude@...hat.com>
To:     Ben Skeggs <skeggsb@...il.com>
Cc:     nouveau@...ts.freedesktop.org, David Airlie <airlied@...ux.ie>,
        linux-kernel@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        Ben Skeggs <bskeggs@...hat.com>, stable@...r.kernel.org
Subject: Re: [PATCH v2] drm/nouveau/i2c: Disable i2c bus access after
 ->fini()

On Thu, 2019-04-11 at 08:48 +1000, Ben Skeggs wrote:
> On Wed, 10 Apr 2019 at 06:23, Lyude Paul <lyude@...hat.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?

That should be fine as long as we don't use pads independently of their i2c
busses (e.g. within nvkm for thermal sensors or the like), but I didn't take
the time to check whether that's true or not. Do you know?

> 
> Thanks,
> Ben.
> 
> > Signed-off-by: Lyude Paul <lyude@...hat.com>
> > Cc: stable@...r.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
> > 
> > _______________________________________________
> > dri-devel mailing list
> > dri-devel@...ts.freedesktop.org
> > https://lists.freedesktop.org/mailman/listinfo/dri-devel
-- 
Cheers,
	Lyude Paul

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