drm/i915/tgl: Fix the read of the DDI that transcoder is attached to

On TGL this register do not map directly to port, it was already
handled when setting it(TGL_TRANS_DDI_SELECT_PORT()) but not when
reading it.

To make it consisntent adding a macro for the older gens too.

v2:
Adding TGL_PORT_TRANS_DDI_SELECT() so all future users can reuse it
(Lucas)

v3:
Missed parentheses arround val (Jose)

v4:
Renamed TGL_PORT_TRANS_DDI_SELECT to TGL_TRANS_DDI_FUNC_CTL_VAL_TO_PORT
(Lucas)
Added TRANS_DDI_FUNC_CTL_VAL_TO_PORT (Lucas)
Reviewed-by: Lucas De Marchi <lucas.demarchi@intel.com>
Cc: Lucas De Marchi <lucas.demarchi@intel.com>
Signed-off-by: José Roberto de Souza <jose.souza@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190808004935.1787-2-jose.souza@intel.com

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

@@ -10354,10 +10354,9 @@ static void haswell_get_ddi_port_state(struct intel_crtc *crtc,
 	tmp = I915_READ(TRANS_DDI_FUNC_CTL(pipe_config->cpu_transcoder));
 
 	if (INTEL_GEN(dev_priv) >= 12)
-		port = (tmp & TGL_TRANS_DDI_PORT_MASK) >>
-			TGL_TRANS_DDI_PORT_SHIFT;
+		port = TGL_TRANS_DDI_FUNC_CTL_VAL_TO_PORT(tmp);
 	else
-		port = (tmp & TRANS_DDI_PORT_MASK) >> TRANS_DDI_PORT_SHIFT;
+		port = TRANS_DDI_FUNC_CTL_VAL_TO_PORT(tmp);
 
 	if (INTEL_GEN(dev_priv) >= 11)
 		icelake_get_ddi_pll(dev_priv, port, pipe_config);

drivers/gpu/drm/i915/i915_reg.h

@@ -9432,6 +9432,8 @@ enum skl_power_gate {
 #define  TGL_TRANS_DDI_PORT_MASK	(0xf << TGL_TRANS_DDI_PORT_SHIFT)
 #define  TRANS_DDI_SELECT_PORT(x)	((x) << TRANS_DDI_PORT_SHIFT)
 #define  TGL_TRANS_DDI_SELECT_PORT(x)	(((x) + 1) << TGL_TRANS_DDI_PORT_SHIFT)
+#define  TRANS_DDI_FUNC_CTL_VAL_TO_PORT(val)	 (((val) & TRANS_DDI_PORT_MASK) >> TRANS_DDI_PORT_SHIFT)
+#define  TGL_TRANS_DDI_FUNC_CTL_VAL_TO_PORT(val) (((val) & TGL_TRANS_DDI_PORT_MASK >> TGL_TRANS_DDI_PORT_SHIFT) - 1)
 #define  TRANS_DDI_MODE_SELECT_MASK	(7 << 24)
 #define  TRANS_DDI_MODE_SELECT_HDMI	(0 << 24)
 #define  TRANS_DDI_MODE_SELECT_DVI	(1 << 24)