drm/i915/tgl: Read SAGV block time from PCODE

Starting from TGL, we now need to read the SAGV block time via a PCODE
mailbox, rather than having a static value.

BSpec: 49326

v2: Fix up pcode val data type (Ville), tighten variable scope (Ville)

Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Cc: Stanislav Lisovskiy <stanislav.lisovskiy@intel.com>
Cc: Lucas De Marchi <lucas.demarchi@intel.com>
Signed-off-by: James Ausmus <james.ausmus@intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Lucas De Marchi <lucas.demarchi@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20191004221449.1317-2-james.ausmus@intel.com
Link: https://patchwork.freedesktop.org/patch/msgid/20191009172315.11004-2-lucas.demarchi@intel.com

drivers/gpu/drm/i915/i915_reg.h

@@ -8878,6 +8878,7 @@ enum {
 #define     GEN9_SAGV_DISABLE			0x0
 #define     GEN9_SAGV_IS_DISABLED		0x1
 #define     GEN9_SAGV_ENABLE			0x3
+#define GEN12_PCODE_READ_SAGV_BLOCK_TIME_US	0x23
 #define GEN6_PCODE_DATA				_MMIO(0x138128)
 #define   GEN6_PCODE_FREQ_IA_RATIO_SHIFT	8
 #define   GEN6_PCODE_FREQ_RING_RATIO_SHIFT	16

drivers/gpu/drm/i915/intel_pm.c

@@ -3641,7 +3641,20 @@ intel_has_sagv(struct drm_i915_private *dev_priv)
 static void
 skl_setup_sagv_block_time(struct drm_i915_private *dev_priv)
 {
-	if (IS_GEN(dev_priv, 11)) {
+	if (INTEL_GEN(dev_priv) >= 12) {
+		u32 val = 0;
+		int ret;
+
+		ret = sandybridge_pcode_read(dev_priv,
+					     GEN12_PCODE_READ_SAGV_BLOCK_TIME_US,
+					     &val, NULL);
+		if (!ret) {
+			dev_priv->sagv_block_time_us = val;
+			return;
+		}
+
+		DRM_DEBUG_DRIVER("Couldn't read SAGV block time!\n");
+	} else if (IS_GEN(dev_priv, 11)) {
 		dev_priv->sagv_block_time_us = 10;
 		return;
 	} else if (IS_GEN(dev_priv, 10)) {