[Bug 93768] [BAT SKL] GPU death starting with first symptom: WARNING backtrace: "DC6 already programmed to be enabled."

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=93768

--- Comment #4 from Mika Kuoppala <mika.kuoppala at intel.com> ---
(In reply to Chris Wilson from comment #2)
> diff --git a/drivers/gpu/drm/i915/intel_runtime_pm.c
> b/drivers/gpu/drm/i915/inte
> index bbca527..a90d4d0 100644
> --- a/drivers/gpu/drm/i915/intel_runtime_pm.c
> +++ b/drivers/gpu/drm/i915/intel_runtime_pm.c
> @@ -497,7 +497,8 @@ static void gen9_set_dc_state(struct drm_i915_private
> *dev_p
>         val &= ~mask;
>         val |= state;
>         I915_WRITE(DC_STATE_EN, val);
> -       POSTING_READ(DC_STATE_EN);
> +       if (wait_for((I915_READ(DC_STATE_EN) & mask) == state, 500))
> +               DRM_ERROR("Timeout whilst enabling DC6\n");
>  }
>  
>  void bxt_enable_dc9(struct drm_i915_private *dev_priv)

Indeed something goes wrong around here. Sometimes when we disable,
DC6 stays disabled for only short amount of time (and/or few reads) but it pops
back up as enabled. Thats still a mystery.

But what happens next is that we have DC6 ON and we try to reset, and
apparently the resetting while on dc6 doesn't lead to success.

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