drm/i915: Transform WaDisableI2mCycleOnWRPort into a simple reg write

GAMT_CHKN_BIT_REG does not live in the context.

Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Mika Kuoppala <mika.kuoppala@intel.com>
Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
Signed-off-by: Oscar Mateo <oscar.mateo@intel.com>
Reviewed-by: Michał Winiarski <michal.winiarski@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/1504798809-5653-2-git-send-email-oscar.mateo@intel.com
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>

drivers/gpu/drm/i915/intel_engine_cs.c

@@ -1072,10 +1072,11 @@ static int cnl_init_workarounds(struct intel_engine_cs *engine)
 	struct drm_i915_private *dev_priv = engine->i915;
 	int ret;
 
-	/* WaDisableI2mCycleOnWRPort: cnl (pre-prod) */
+	/* WaDisableI2mCycleOnWRPort:cnl (pre-prod) */
 	if (IS_CNL_REVID(dev_priv, CNL_REVID_B0, CNL_REVID_B0))
-		WA_SET_BIT(GAMT_CHKN_BIT_REG,
-			   GAMT_CHKN_DISABLE_I2M_CYCLE_ON_WR_PORT);
+		I915_WRITE(GAMT_CHKN_BIT_REG,
+			   (I915_READ(GAMT_CHKN_BIT_REG) |
+			    GAMT_CHKN_DISABLE_I2M_CYCLE_ON_WR_PORT));
 
 	/* WaForceContextSaveRestoreNonCoherent:cnl */
 	WA_SET_BIT_MASKED(CNL_HDC_CHICKEN0,