drm/i915: Reboot CI if forcewake fails

If the HW fails to ack a change in forcewake status, the machine is as
good as dead -- it may recover, but in reality it missed the mmio
updates and is now in a very inconsistent state. If it happens, we can't
trust the CI results (or at least the fails may be genuine but due to
the HW being dead and not the actual test!) so reboot the machine (CI
checks for a kernel taint in between each test and reboots if the
machine is tainted).
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Cc: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>
Reviewed-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190508115245.27790-1-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/gt/intel_reset.c

@@ -1042,7 +1042,7 @@ void i915_reset(struct drm_i915_private *i915,
 	 * rather than continue on into oblivion. For everyone else,
 	 * the system should still plod along, but they have been warned!
 	 */
-	add_taint(TAINT_WARN, LOCKDEP_STILL_OK);
+	add_taint_for_CI(TAINT_WARN);
 error:
 	__i915_gem_set_wedged(i915);
 	goto finish;

drivers/gpu/drm/i915/i915_drv.h

@@ -3375,4 +3375,15 @@ static inline u32 i915_scratch_offset(const struct drm_i915_private *i915)
 	return i915_ggtt_offset(i915->gt.scratch);
 }
 
+static inline void add_taint_for_CI(unsigned int taint)
+{
+	/*
+	 * The system is "ok", just about surviving for the user, but
+	 * CI results are now unreliable as the HW is very suspect.
+	 * CI checks the taint state after every test and will reboot
+	 * the machine if the kernel is tainted.
+	 */
+	add_taint(taint, LOCKDEP_STILL_OK);
+}
+
 #endif

drivers/gpu/drm/i915/intel_uncore.c

@@ -111,9 +111,11 @@ wait_ack_set(const struct intel_uncore_forcewake_domain *d,
 static inline void
 fw_domain_wait_ack_clear(const struct intel_uncore_forcewake_domain *d)
 {
-	if (wait_ack_clear(d, FORCEWAKE_KERNEL))
+	if (wait_ack_clear(d, FORCEWAKE_KERNEL)) {
 		DRM_ERROR("%s: timed out waiting for forcewake ack to clear.\n",
 			  intel_uncore_forcewake_domain_to_str(d->id));
+		add_taint_for_CI(TAINT_WARN); /* CI now unreliable */
+	}
 }
 
 enum ack_type {
@@ -186,9 +188,11 @@ fw_domain_get(const struct intel_uncore_forcewake_domain *d)
 static inline void
 fw_domain_wait_ack_set(const struct intel_uncore_forcewake_domain *d)
 {
-	if (wait_ack_set(d, FORCEWAKE_KERNEL))
+	if (wait_ack_set(d, FORCEWAKE_KERNEL)) {
 		DRM_ERROR("%s: timed out waiting for forcewake ack request.\n",
 			  intel_uncore_forcewake_domain_to_str(d->id));
+		add_taint_for_CI(TAINT_WARN); /* CI now unreliable */
+	}
 }
 
 static inline void