drm/i915/perf: simplify OA unit enabling on gen7

In commit d7965152 ("drm/i915: Enable i915 perf stream for
Haswell OA unit") the enable/disable vfunc hadn't appear yet and the
same function would deal with enabling/disabling the OA unit.

This was split later on for gen8 but the gen7 retained some code that
isn't actually useful anymore.
Signed-off-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Reviewed-by: Matthew Auld <matthew.auld@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180326090831.22686-4-lionel.g.landwerlin@intel.com

drivers/gpu/drm/i915/i915_perf.c

@@ -1886,6 +1886,13 @@ static void gen10_disable_metric_set(struct drm_i915_private *dev_priv)
 
 static void gen7_oa_enable(struct drm_i915_private *dev_priv)
 {
+	struct i915_gem_context *ctx =
+			dev_priv->perf.oa.exclusive_stream->ctx;
+	u32 ctx_id = dev_priv->perf.oa.specific_ctx_id;
+	bool periodic = dev_priv->perf.oa.periodic;
+	u32 period_exponent = dev_priv->perf.oa.period_exponent;
+	u32 report_format = dev_priv->perf.oa.oa_buffer.format;
+
 	/*
 	 * Reset buf pointers so we don't forward reports from before now.
 	 *
@@ -1897,15 +1904,6 @@ static void gen7_oa_enable(struct drm_i915_private *dev_priv)
 	 */
 	gen7_init_oa_buffer(dev_priv);
 
-	if (dev_priv->perf.oa.exclusive_stream->enabled) {
-		struct i915_gem_context *ctx =
-			dev_priv->perf.oa.exclusive_stream->ctx;
-		u32 ctx_id = dev_priv->perf.oa.specific_ctx_id;
-
-		bool periodic = dev_priv->perf.oa.periodic;
-		u32 period_exponent = dev_priv->perf.oa.period_exponent;
-		u32 report_format = dev_priv->perf.oa.oa_buffer.format;
-
 	I915_WRITE(GEN7_OACONTROL,
 		   (ctx_id & GEN7_OACONTROL_CTX_MASK) |
 		   (period_exponent <<
@@ -1914,8 +1912,6 @@ static void gen7_oa_enable(struct drm_i915_private *dev_priv)
 		   (report_format << GEN7_OACONTROL_FORMAT_SHIFT) |
 		   (ctx ? GEN7_OACONTROL_PER_CTX_ENABLE : 0) |
 		   GEN7_OACONTROL_ENABLE);
-	} else
-		I915_WRITE(GEN7_OACONTROL, 0);
 }
 
 static void gen8_oa_enable(struct drm_i915_private *dev_priv)