drm/i915/dsi: Extract port_ctrl_reg()

The code to determine the pre-ICL DSI port control register is
repeated several times. Consolidate.

vlv_dsi_clear_device_ready() is left with the open-coded version
due to the weirdness with port A vs. C on VLV/CHV.
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20231101114212.9345-6-ville.syrjala@linux.intel.comReviewed-by: Jani Nikula <jani.nikula@intel.com>

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

@@ -561,6 +561,12 @@ static void glk_dsi_clear_device_ready(struct intel_encoder *encoder)
 	glk_dsi_disable_mipi_io(encoder);
 }
 
+static i915_reg_t port_ctrl_reg(struct drm_i915_private *i915, enum port port)
+{
+	return IS_GEMINILAKE(i915) || IS_BROXTON(i915) ?
+		BXT_MIPI_PORT_CTRL(port) : MIPI_PORT_CTRL(port);
+}
+
 static void vlv_dsi_clear_device_ready(struct intel_encoder *encoder)
 {
 	struct drm_i915_private *dev_priv = to_i915(encoder->base.dev);
@@ -627,8 +633,7 @@ static void intel_dsi_port_enable(struct intel_encoder *encoder,
 	}
 
 	for_each_dsi_port(port, intel_dsi->ports) {
-		i915_reg_t port_ctrl = IS_GEMINILAKE(dev_priv) || IS_BROXTON(dev_priv) ?
-			BXT_MIPI_PORT_CTRL(port) : MIPI_PORT_CTRL(port);
+		i915_reg_t port_ctrl = port_ctrl_reg(dev_priv, port);
 		u32 temp;
 
 		temp = intel_de_read(dev_priv, port_ctrl);
@@ -664,8 +669,7 @@ static void intel_dsi_port_disable(struct intel_encoder *encoder)
 	enum port port;
 
 	for_each_dsi_port(port, intel_dsi->ports) {
-		i915_reg_t port_ctrl = IS_GEMINILAKE(dev_priv) || IS_BROXTON(dev_priv) ?
-			BXT_MIPI_PORT_CTRL(port) : MIPI_PORT_CTRL(port);
+		i915_reg_t port_ctrl = port_ctrl_reg(dev_priv, port);
 
 		/* de-assert ip_tg_enable signal */
 		intel_de_rmw(dev_priv, port_ctrl, DPI_ENABLE, 0);
@@ -955,9 +959,8 @@ static bool intel_dsi_get_hw_state(struct intel_encoder *encoder,
 
 	/* XXX: this only works for one DSI output */
 	for_each_dsi_port(port, intel_dsi->ports) {
-		i915_reg_t ctrl_reg = IS_GEMINILAKE(dev_priv) || IS_BROXTON(dev_priv) ?
-			BXT_MIPI_PORT_CTRL(port) : MIPI_PORT_CTRL(port);
-		bool enabled = intel_de_read(dev_priv, ctrl_reg) & DPI_ENABLE;
+		i915_reg_t port_ctrl = port_ctrl_reg(dev_priv, port);
+		bool enabled = intel_de_read(dev_priv, port_ctrl) & DPI_ENABLE;
 
 		/*
 		 * Due to some hardware limitations on VLV/CHV, the DPI enable