drm/i915: Generalise common GPU engine reset request/unrequest code

GPU engine reset handshaking is something that is applicable to both full GPU
reset and engine reset, which is something that is part of the upcoming TDR
per-engine hang recovery patches. Break out the common engine reset
request/unrequest code (originally written by Mika Kuoppala) for reuse later
in the TDR enablement patch series.

v2: correct indentation and drop unused returned value (Mika)
v3: We have forcewake during reset so use *_FW reg access (Mika)
Reviewed-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Signed-off-by: Tomas Elf <tomas.elf@intel.com>
Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Signed-off-by: Arun Siluvery <arun.siluvery@linux.intel.com>
[Mika: Fixed format warning]
Signed-off-by: Mika Kuoppala <mika.kuoppala@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1456929984-16323-1-git-send-email-mika.kuoppala@intel.com

drivers/gpu/drm/i915/intel_uncore.c

@@ -1531,41 +1531,57 @@ static int gen6_do_reset(struct drm_device *dev)
 	return ret;
 }
 
-static int wait_for_register(struct drm_i915_private *dev_priv,
+static int wait_for_register_fw(struct drm_i915_private *dev_priv,
 				i915_reg_t reg,
 				const u32 mask,
 				const u32 value,
 				const unsigned long timeout_ms)
 {
-	return wait_for((I915_READ(reg) & mask) == value, timeout_ms);
+	return wait_for((I915_READ_FW(reg) & mask) == value, timeout_ms);
 }
 
-static int gen8_do_reset(struct drm_device *dev)
+static int gen8_request_engine_reset(struct intel_engine_cs *engine)
 {
-	struct drm_i915_private *dev_priv = dev->dev_private;
-	struct intel_engine_cs *engine;
-	int i;
+	int ret;
+	struct drm_i915_private *dev_priv = engine->dev->dev_private;
 
-	for_each_ring(engine, dev_priv, i) {
-		I915_WRITE(RING_RESET_CTL(engine->mmio_base),
+	I915_WRITE_FW(RING_RESET_CTL(engine->mmio_base),
 		      _MASKED_BIT_ENABLE(RESET_CTL_REQUEST_RESET));
 
-		if (wait_for_register(dev_priv,
+	ret = wait_for_register_fw(dev_priv,
 				   RING_RESET_CTL(engine->mmio_base),
 				   RESET_CTL_READY_TO_RESET,
 				   RESET_CTL_READY_TO_RESET,
-				      700)) {
+				   700);
+	if (ret)
 		DRM_ERROR("%s: reset request timeout\n", engine->name);
+
+	return ret;
+}
+
+static void gen8_unrequest_engine_reset(struct intel_engine_cs *engine)
+{
+	struct drm_i915_private *dev_priv = engine->dev->dev_private;
+
+	I915_WRITE_FW(RING_RESET_CTL(engine->mmio_base),
+		      _MASKED_BIT_DISABLE(RESET_CTL_REQUEST_RESET));
+}
+
+static int gen8_do_reset(struct drm_device *dev)
+{
+	struct drm_i915_private *dev_priv = dev->dev_private;
+	struct intel_engine_cs *engine;
+	int i;
+
+	for_each_ring(engine, dev_priv, i)
+		if (gen8_request_engine_reset(engine))
 			goto not_ready;
-		}
-	}
 
 	return gen6_do_reset(dev);
 
 not_ready:
 	for_each_ring(engine, dev_priv, i)
-		I915_WRITE(RING_RESET_CTL(engine->mmio_base),
-			   _MASKED_BIT_DISABLE(RESET_CTL_REQUEST_RESET));
+		gen8_unrequest_engine_reset(engine);
 
 	return -EIO;
 }