[Intel-gfx] [PATCH 1/2] drm/i915: clear up wedged transitions

[Damien Lespiau]

On Thu, Nov 15, 2012 at 4:17 PM, Daniel Vetter <daniel.vetter at ffwll.ch> wrote:
> We have two important transitions of the wedged state in the current
> code:
>
> - 0 -> 1: This means a hang has been detected, and signals to everyone
>   that they please get of any locks, so that the reset work item can
>   do its job.
>
> - 1 -> 0: The reset handler has completed.
>
> Now the last transition mixes up two states: "Reset completed and
> successful" and "Reset failed". To distinguish these two we do some
> tricks with the reset completion, but I simply could not convince
> myself that this doesn't race under odd circumstances.
>
> Hence split this up, and add a new terminal state indicating that the
> hw is gone for good.
>
> Also add explicit #defines for both states, update comments.
>
> v2: Split out the reset handling bugfix for the throttle ioctl.
>
> v3: s/tmp/wedged/ sugested by Chris Wilson. Also fixup up a rebase
> error which prevented this patch from actually compiling.
>
> v4: To unify the wedged state with the reset counter, keep the
> reset-in-progress state just as a flag. The terminally-wedged state is
> now denoted with a big number.
>
> v5: Add a comment to the reset_counter special values explaining that
> WEDGED & RESET_IN_PROGRESS needs to be true for the code to be
> correct.
>
> v6: Fixup logic errors introduced with the wedged+reset_counter
> unification. Since WEDGED implies reset-in-progress (in a way we're
> terminally stuck in the dead-but-reset-not-completed state), we need
> ensure that we check for this everywhere. The specific bug was in
> wait_for_error, which would simply have timed out.
>
> v7: Extract an inline i915_reset_in_progress helper to make the code
> more readable. Also annote the reset-in-progress case with an
> unlikely, to help the compiler optimize the fastpath. Do the same for
> the terminally wedged case with i915_terminally_wedged.
>
> Signed-Off-by: Daniel Vetter <daniel.vetter at ffwll.ch>

Right, so the usage of a wait queue makes the code quite a bit more
understandable I had to scratch my head for quite a bit with the
x->done poking.

I think I'd have love to see the "completion -> wait_queue + 2 reset
states" and the "gpu_error.wedge -> gpu_error.reset_counter"
transitions as two different patches (well, I did because of the 2
versions sent, so all is good)

Reviewed-by: Damien Lespiau <damien.lespiau at intel.com>

-- 
Damien