drm/i915/psr: Add helpers for block count number handling

Add helpers to make it more clear how PSR2_CTL[Block Count Number]
is configured.
Signed-off-by: Jouni Högander <jouni.hogander@intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230329150703.432072-5-jouni.hogander@intel.com

drivers/gpu/drm/i915/display/intel_psr.c

@@ -519,6 +519,17 @@ static u32 intel_psr2_get_tp_time(struct intel_dp *intel_dp)
 	return val;
 }
 
+static int psr2_block_count_lines(struct intel_dp *intel_dp)
+{
+	return intel_dp->psr.io_wake_lines < 9 &&
+		intel_dp->psr.fast_wake_lines < 9 ? 8 : 12;
+}
+
+static int psr2_block_count(struct intel_dp *intel_dp)
+{
+	return psr2_block_count_lines(intel_dp) / 4;
+}
+
 static void hsw_activate_psr2(struct intel_dp *intel_dp)
 {
 	struct drm_i915_private *dev_priv = dp_to_i915(intel_dp);
@@ -536,11 +547,10 @@ static void hsw_activate_psr2(struct intel_dp *intel_dp)
 	val |= intel_psr2_get_tp_time(intel_dp);
 
 	if (DISPLAY_VER(dev_priv) >= 12) {
-		if (intel_dp->psr.io_wake_lines < 9 &&
-		    intel_dp->psr.fast_wake_lines < 9)
-			val |= TGL_EDP_PSR2_BLOCK_COUNT_NUM_2;
-		else
+		if (psr2_block_count(intel_dp) > 2)
 			val |= TGL_EDP_PSR2_BLOCK_COUNT_NUM_3;
+		else
+			val |= TGL_EDP_PSR2_BLOCK_COUNT_NUM_2;
 	}
 
 	/* Wa_22012278275:adl-p */