Re: [PATCH] drm/i915: Allow unready gpu to be reset on gen8

Daniel Vetter
2015-11-17T17:40:36Z

On Mon, Nov 02, 2015 at 11:25:08AM +0200, Mika Kuoppala wrote:
> Gen9 has had demonstrated cases where forcing a not ready gpu
> into reset has caused system hang [1].
>
> Gen8 has never to this date demonstrated such behaviour.
>
> In our CI tests there have been two cases of bsw ending in a state
> where it claims it is not ready for reset, based on reset request,
> after gpu hang [2]. Both of these cases have happened with kernel
> where there are lots of debugs enabled. So it is possible that
> something timing related is at play here like that wait_for_register()
> usleep wakeups collide badly with forcewake.
>
> If we assume that gen8 is safe to reset even with claims of nonreadiness,
> we can alleviate this situations by forcing a reset and revive the gpu.
> Enhance logging so that it will be clear what conditions led to decision
> of proceeding or bailing out, so that we will spot if this way of forcing
> our will against gpu turns out to be foolhardy.
>
> v2: - add bugzilla entry for bsw behaviour (Chris)
> - improve commit message
>
> References [1]: https://bugs.freedesktop.org/show_bug.cgi?id=89959
> References [2]: https://bugs.freedesktop.org/show_bug.cgi?id=92774
> Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
> Cc: Tomi Sarvela <tomix.p.sarvela@intel.com>
> Cc: Chris Wilson <chris@chris-wilson.co.uk>
> Signed-off-by: Mika Kuoppala <mika.kuoppala@intel.com>
> ---
> drivers/gpu/drm/i915/intel_uncore.c | 9 ++++++++-
> 1 file changed, 8 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/i915/intel_uncore.c b/drivers/gpu/drm/i915/intel_uncore.c
> index f0f97b2..47c17f2 100644
> --- a/drivers/gpu/drm/i915/intel_uncore.c
> +++ b/drivers/gpu/drm/i915/intel_uncore.c
> @@ -1504,7 +1504,14 @@ not_ready:
> I915_WRITE(RING_RESET_CTL(engine->mmio_base),
> _MASKED_BIT_DISABLE(RESET_CTL_REQUEST_RESET));
>
> - return -EIO;
> + if (INTEL_INFO(dev)->gen == 9) {
> + DRM_ERROR("Reset would risk system stability, bailing out\n");
> + return -EIO;
> + }
> +
> + DRM_ERROR("Forcing non ready gpu into reset\n");

DRM_ERROR will cause dmes-warn failures when running igt. If we agree that
this is ok, it should be at most DRM_INFO. I'd got with DRM_DEBUG_DRIVER.
Ack with that change.
-Daniel

> +
> + return gen6_do_reset(dev);
> }
>
> static int (*intel_get_gpu_reset(struct drm_device *dev))(struct drm_device *)
> --
> 2.5.0
>

--
Daniel Vetter
Software Engineer, Intel Corporation