drm/i915: Extract CSB status read

This is a useful thing to have around as a function because the mechanism may
change in the future.

There is a net increase in LOC here, and it will continue to be the case on GEN8
and GEN9 - but future GENs may have an alternate mechanism for doing this.
Signed-off-by: NBen Widawsky <benjamin.widawsky@intel.com>
Reviewed-by: NMichel Thierry <michel.thierry@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1452018609-10142-4-git-send-email-benjamin.widawsky@intel.comSigned-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/intel_lrc.c

@@ -496,6 +496,19 @@ static bool execlists_check_remove_request(struct intel_engine_cs *ring,
 	return false;
 }
 
+static void get_context_status(struct intel_engine_cs *ring,
+			       u8 read_pointer,
+			       u32 *status, u32 *context_id)
+{
+	struct drm_i915_private *dev_priv = ring->dev->dev_private;
+
+	if (WARN_ON(read_pointer >= GEN8_CSB_ENTRIES))
+		return;
+
+	*status = I915_READ(RING_CONTEXT_STATUS_BUF_LO(ring, read_pointer));
+	*context_id = I915_READ(RING_CONTEXT_STATUS_BUF_HI(ring, read_pointer));
+}
+
 /**
  * intel_lrc_irq_handler() - handle Context Switch interrupts
  * @ring: Engine Command Streamer to handle.
@@ -523,9 +536,9 @@ void intel_lrc_irq_handler(struct intel_engine_cs *ring)
 	spin_lock(&ring->execlist_lock);
 
 	while (read_pointer < write_pointer) {
-		read_pointer++;
-		status = I915_READ(RING_CONTEXT_STATUS_BUF_LO(ring, read_pointer % GEN8_CSB_ENTRIES));
-		status_id = I915_READ(RING_CONTEXT_STATUS_BUF_HI(ring, read_pointer % GEN8_CSB_ENTRIES));
+
+		get_context_status(ring, ++read_pointer % GEN8_CSB_ENTRIES,
+				   &status, &status_id);
 
 		if (status & GEN8_CTX_STATUS_IDLE_ACTIVE)
 			continue;