Re: [PATCH 1/2] drm/nouveau/bar/gf100: fix hang when calling ->fini() before ->init()

[Guillaume Tucker]

On 05/12/17 18:32, Ben Skeggs wrote:
> On Wed, Dec 6, 2017 at 12:30 AM, Jon Hunter <jonathanh@xxxxxxxxxx> wrote:
>
> > On 04/12/17 18:37, Guillaume Tucker wrote:
> > > If the firmware fails to load then ->fini() will be called before the
> > > device has been initialised, causing the kernel to hang while trying
> > > to write to a register.  Add a test in ->fini() to avoid this issue.
> > >
> > > This fixes a kernel hang on tegra124.
> > >
> > > Fixes: b17de35a2ebbe ("drm/nouveau/bar: implement bar1 teardown")
> > > Signed-off-by: Guillaume Tucker <guillaume.tucker@xxxxxxxxxxxxx>
> > > CC: Ben Skeggs <bskeggs@xxxxxxxxxx>
> > > ---
> > >  drivers/gpu/drm/nouveau/nvkm/subdev/bar/gf100.c | 7 +++++--
> > >  1 file changed, 5 insertions(+), 2 deletions(-)
> > >
> > > diff --git a/drivers/gpu/drm/nouveau/nvkm/subdev/bar/gf100.c
> > b/drivers/gpu/drm/nouveau/nvkm/subdev/bar/gf100.c
> > > index a3ba7f50198b..95e2aba64aad 100644
> > > --- a/drivers/gpu/drm/nouveau/nvkm/subdev/bar/gf100.c
> > > +++ b/drivers/gpu/drm/nouveau/nvkm/subdev/bar/gf100.c
> > > @@ -43,9 +43,12 @@ gf100_bar_bar1_wait(struct nvkm_bar *base)
> > >  }
> > >
> > >  void
> > > -gf100_bar_bar1_fini(struct nvkm_bar *bar)
> > > +gf100_bar_bar1_fini(struct nvkm_bar *base)
> > >  {
> > > -     nvkm_mask(bar->subdev.device, 0x001704, 0x80000000, 0x00000000);
> > > +     struct nvkm_device *device = base->subdev.device;
> > > +
> > > +     if (base->subdev.oneinit)
> > > +             nvkm_mask(device, 0x001704, 0x80000000, 0x00000000);
> > >  }
> > >
> > >  void
> >
> > I have tested this and it works for me. Thanks for fixing this! Would be
> > good to get Ben's ACK, but you can have my ...
> I'd love to get a good explanation as to why it hangs without this change,
> as, on the surface, it's not immediately obvious as to why it's hanging.

To be fair I'm not entirely sure either why this causes a hang, I
haven't read the TRM...  The iomem has been mapped at this point,
so accessing the register should work.  One clue is when you look
at _bar1_init(), the 0x1704 register is initialised with
some (device instance?) memory address.  So it's possible that
the hardware does something special when you set this to 0 as in
_bar1_fini(), which may fail in particular if it was previously
not initialised with a valid address.

This is merely guesswork, would be interested to find out the
real explanation though.

> > Tested-by: Jon Hunter <jonathanh@xxxxxxxxxx>

Thanks!

Guillaume