[Intel-gfx] [PATCH 2/2] drm/i915/g4x: Fix unreliable gpu reset

[Chris Wilson]

On Thu, May 18, 2017 at 03:34:22PM +0300, Mika Kuoppala wrote:
> ELK seems to very picky about the preconditions to reset.
> Evidence on Eaglelake (8086:2e12 (rev 03)) shows that it does
> not like if reset occurs when there is active ring.
> 
> Ville found out that there is workaround with name
> 'WaMediaResetMainRingCleanup' which suggests that we need to
> cleanup rings before resetting. It is unclear what cleanup
> exactly means but evidence shows that stopping the ring
> does have an effect on reset reliability.
> 
> Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=100998
> Suggested-by: Ville Syrjälä <ville.syrjala at linux.intel.com>
> Cc: Ville Syrjälä <ville.syrjala at linux.intel.com>
> Cc: Chris Wilson <chris at chris-wilson.co.uk>
> Cc: Tomi Sarvela <tomi.p.sarvela at intel.com>
> Signed-off-by: Mika Kuoppala <mika.kuoppala at intel.com>
> ---
>  drivers/gpu/drm/i915/intel_uncore.c | 26 ++++++++++++++++++++++++++
>  1 file changed, 26 insertions(+)
> 
> diff --git a/drivers/gpu/drm/i915/intel_uncore.c b/drivers/gpu/drm/i915/intel_uncore.c
> index 7eaaf2225e1a..1d473cd1f8a4 100644
> --- a/drivers/gpu/drm/i915/intel_uncore.c
> +++ b/drivers/gpu/drm/i915/intel_uncore.c
> @@ -1427,6 +1427,26 @@ int i915_reg_read_ioctl(struct drm_device *dev,
>  	return ret;
>  }
>  
> +static void gen3_stop_rings(struct drm_i915_private *dev_priv)
> +{
> +	struct intel_engine_cs *engine;
> +	enum intel_engine_id id;
> +
> +	for_each_engine(engine, dev_priv, id) {
> +		const i915_reg_t mode_r = RING_MI_MODE(engine->mmio_base);
> +
> +		I915_WRITE_FW(mode_r, _MASKED_BIT_ENABLE(STOP_RING));

This will only stop between instructions on the CS (i.e. within the
ring) aiui . If we did hang in a shader, this is not going to achieve
very much.

> +		if (intel_wait_for_register_fw(dev_priv,
> +					       mode_r,
> +					       MODE_IDLE,
> +					       MODE_IDLE,
> +					       1000)) {
> +			DRM_DEBUG("%s : timed out STOP_RING\n",
> +				  engine->name);

If we make this a DRM_ERROR I expect it to fire through the hang tests
in BAT.
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre