drm/i915: Add Wa_1407352427:icl,ehl

The workaround database now indicates we need to disable psdunit clock
gating as well.

v3:
 - Rebase on top of other workarounds that have landed.
 - Restrict cc:stable tag to 5.2+ since that's when ICL was first
   officially supported.

Bspec: 32354
Bspec: 33450
Bspec: 33451
Suggested-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Cc: stable@vger.kernel.org # v5.2+
Cc: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Cc: Lucas De Marchi <lucas.demarchi@intel.com>
Cc: Matt Atwood <matthew.s.atwood@intel.com>
Signed-off-by: Matt Roper <matthew.d.roper@intel.com>
Acked-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20191231190713.1549533-1-matthew.d.roper@intel.com

drivers/gpu/drm/i915/i915_reg.h

@@ -4183,6 +4183,7 @@ enum {
 
 #define UNSLICE_UNIT_LEVEL_CLKGATE2	_MMIO(0x94e4)
 #define   VSUNIT_CLKGATE_DIS_TGL	REG_BIT(19)
+#define   PSDUNIT_CLKGATE_DIS		REG_BIT(5)
 
 #define INF_UNIT_LEVEL_CLKGATE		_MMIO(0x9560)
 #define   CGPSF_CLKGATE_DIS		(1 << 3)

drivers/gpu/drm/i915/intel_pm.c

@@ -6607,6 +6607,9 @@ static void icl_init_clock_gating(struct drm_i915_private *dev_priv)
 	intel_uncore_rmw(&dev_priv->uncore, UNSLICE_UNIT_LEVEL_CLKGATE,
 			 0, VSUNIT_CLKGATE_DIS | HSUNIT_CLKGATE_DIS);
 
+	/* Wa_1407352427:icl,ehl */
+	intel_uncore_rmw(&dev_priv->uncore, UNSLICE_UNIT_LEVEL_CLKGATE2,
+			 0, PSDUNIT_CLKGATE_DIS);
 }
 
 static void tgl_init_clock_gating(struct drm_i915_private *dev_priv)