[Intel-gfx] [PATCH] drm/i915: Clear stop-engine for a pardoned reset

[Chris Wilson]

Quoting Mika Kuoppala (2018-08-15 10:08:09)
> Chris Wilson <chris at chris-wilson.co.uk> writes:
> 
> > Quoting Mika Kuoppala (2018-08-15 09:52:18)
> >> Chris Wilson <chris at chris-wilson.co.uk> writes:
> >> 
> >> > If we pardon a per-engine reset, we may leave the STOP_RING bit asserted
> >> > in RING_MI_MODE resulting in the engine hanging. Unconditionally clear
> >> > it on the per-engine exit path as we know that either we skipped the
> >> > reset and so need the cancellation, or the reset was successful and the
> >> > cancellation is a no-op, or there was an error and we will follow up
> >> > with a full-reset or wedging (both of which will stop the engines again
> >> > as required).
> >> >
> >> > Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
> >> > Cc: Mika Kuoppala <mika.kuoppala at linux.intel.com>
> >> > ---
> >> >  drivers/gpu/drm/i915/i915_drv.c         |  1 +
> >> >  drivers/gpu/drm/i915/intel_engine_cs.c  | 10 ++++++++++
> >> >  drivers/gpu/drm/i915/intel_ringbuffer.h |  1 +
> >> >  3 files changed, 12 insertions(+)
> >> >
> >> > diff --git a/drivers/gpu/drm/i915/i915_drv.c b/drivers/gpu/drm/i915/i915_drv.c
> >> > index 9dce55182c3a..41111f2a9c39 100644
> >> > --- a/drivers/gpu/drm/i915/i915_drv.c
> >> > +++ b/drivers/gpu/drm/i915/i915_drv.c
> >> > @@ -2079,6 +2079,7 @@ int i915_reset_engine(struct intel_engine_cs *engine, const char *msg)
> >> >               goto out;
> >> >  
> >> >  out:
> >> > +     intel_engine_cancel_stop_cs(engine);
> >> >       i915_gem_reset_finish_engine(engine);
> >> 
> >> Should we just lift the whole stop/start dance into
> >> gem_reset_prepare|finish_engine()s?
> >
> > No, because it is also used by wedging where we do want the asymmetry.
> > Been there, done that, have the gem_eio bruises.
> 
> On wedge the submission path is blocked but yeah,
> gpu can be in any state and enabling the engine at that
> point is asking for trouble.
> 
> Reviewed-by: Mika Kuoppala <mika.kuoppala at linux.intel.com>

Grabbed, pushed, and scarpered.

Although this should fix the silly STOP_RING hangs that have been
plaguing us for the last few months, there still seems to be more fun to
be had here. /o\
-Chris