drm/i915/g33: Improve reset reliability

We improved the reset reliablity on gen4 with
stopping all engines before commencing reset, in
commit 2c80353f3cd0 ("drm/i915/g4x: Improve gpu reset reliability")

Evidence indicates that this same trick works with g33.

v2: proper gen naming, comment readability (Chris)

Testcase: igt/gem_busy/*-hang #blb-e6850
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Tomi Sarvela <tomi.p.sarvela@intel.com>
Signed-off-by: Mika Kuoppala <mika.kuoppala@intel.com>
Acked-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: http://patchwork.freedesktop.org/patch/msgid/20170522090244.2557-1-mika.kuoppala@intel.com

drivers/gpu/drm/i915/intel_uncore.c

@@ -1488,6 +1488,9 @@ static int g33_do_reset(struct drm_i915_private *dev_priv, unsigned engine_mask)
 {
 	struct pci_dev *pdev = dev_priv->drm.pdev;
 
+	/* Stop engines before we reset; see g4x_do_reset() below for why. */
+	gen3_stop_rings(dev_priv);
+
 	pci_write_config_byte(pdev, I915_GDRST, GRDOM_RESET_ENABLE);
 	return wait_for(g4x_reset_complete(pdev), 500);
 }