Quoting Michel Thierry (2017-12-16 00:48:55)
> On 12/15/2017 4:03 PM, Chris Wilson wrote:
> > As part of the system requirement for powersaving is that we always have
> > a context loaded. Upon boot and resume, we load the kernel_context to
> > ensure that some valid state is set before powersaving kicks in, we
> > should do so after a full GPU reset as well. We only need to do so for
> > an idle engine, as any active engines will restart by executing the
> > stuck request, loading its context, for the idle engine we create a
> > new request to load the kernel_context instead.
> >
> > Signed-off-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
> > Cc: Mika Kuoppala <mika.kuoppala@xxxxxxxxxxxxxxx>
> > Cc: Joonas Lahtinen <joonas.lahtinen@xxxxxxxxxxxxxxx>
> > ---
> > drivers/gpu/drm/i915/i915_gem.c | 9 +++++++++
> > 1 file changed, 9 insertions(+)
> >
> > diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
> > index 4a7f5579a7a5..189725a8fed6 100644
> > --- a/drivers/gpu/drm/i915/i915_gem.c
> > +++ b/drivers/gpu/drm/i915/i915_gem.c
> > @@ -3119,6 +3119,15 @@ void i915_gem_reset(struct drm_i915_private *dev_priv)
> > ctx = fetch_and_zero(&engine->last_retired_context);
> > if (ctx)
> > engine->context_unpin(engine, ctx);
> > +
> > + if (list_empty(&engine->timeline->requests)) {
> > + struct drm_i915_gem_request *rq;
> > +
> > + rq = i915_gem_request_alloc(engine,
> > + dev_priv->kernel_context);
> > + if (!IS_ERR(rq))
> > + __i915_add_request(rq, false);
> > + }
> > }
> >
> > i915_gem_restore_fences(dev_priv);
>
> It shouldn't hurt and if it fixes something,
>
> Reviewed-by: Michel Thierry <michel.thierry@xxxxxxxxx>
Indeed, in that run it fixed both of the mystery hangs, pnv and bdw+.
So I added a comment that it is a mystery fix to hopefully inspire us to
find the real reason, I think I'm on the right lines with stale TLB
something like the lack of INSTPM_TLB_INVALIDATE, and in the meantime to
remember not to remove it.
Thanks for the quick review, I've pushed this and its companion to avoid
resetting the idle engine for per-engine resets. (And fingers crossed
the bandaid holds.)
-Chris
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