drm/i915: Implement WaDisableVFclkgate.

This workaround supposedly fixes some hangs in the VF unit.
Signed-off-by: Rafael Antognolli <rafael.antognolli@intel.com>
Reviewed-by: Lucas De Marchi <lucas.demarchi@intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20171216001117.14232-1-rafael.antognolli@intel.com

drivers/gpu/drm/i915/i915_reg.h

@@ -3875,6 +3875,9 @@ enum {
 #define  SARBUNIT_CLKGATE_DIS		(1 << 5)
 #define  RCCUNIT_CLKGATE_DIS		(1 << 7)
 
+#define UNSLICE_UNIT_LEVEL_CLKGATE	_MMIO(0x9434)
+#define  VFUNIT_CLKGATE_DIS		(1 << 20)
+
 /*
  * Display engine regs
  */

drivers/gpu/drm/i915/intel_pm.c

@@ -8447,6 +8447,11 @@ static void cnl_init_clock_gating(struct drm_i915_private *dev_priv)
 	if (IS_CNL_REVID(dev_priv, CNL_REVID_A0, CNL_REVID_B0))
 		val |= SARBUNIT_CLKGATE_DIS;
 	I915_WRITE(SLICE_UNIT_LEVEL_CLKGATE, val);
+
+	/* WaDisableVFclkgate:cnl */
+	val = I915_READ(UNSLICE_UNIT_LEVEL_CLKGATE);
+	val |= VFUNIT_CLKGATE_DIS;
+	I915_WRITE(UNSLICE_UNIT_LEVEL_CLKGATE, val);
 }
 
 static void cfl_init_clock_gating(struct drm_i915_private *dev_priv)