drm/i915: don't intel_crt_init if DDI A has 4 lanes

DDI A and E have 4 lanes to share, so if DDI A is using 4 lanes,
there's nothing left for DDI E, which means there's no CRT port on the
machine.

The bit we're checking here is programmed at system boot and it cannot
be changed afterwards, so we cannot change the amount of lanes
reserved for each DDI port.

Signed-off-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
Reviewed-by: Damien Lespiau <damien.lespiau@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/i915_reg.h

@@ -4515,6 +4515,7 @@
 #define  DDI_BUF_EMP_800MV_3_5DB_HSW		(8<<24)   /* Sel8 */
 #define  DDI_BUF_EMP_MASK			(0xf<<24)
 #define  DDI_BUF_IS_IDLE			(1<<7)
+#define  DDI_A_4_LANES				(1<<4)
 #define  DDI_PORT_WIDTH_X1			(0<<1)
 #define  DDI_PORT_WIDTH_X2			(1<<1)
 #define  DDI_PORT_WIDTH_X4			(3<<1)

drivers/gpu/drm/i915/intel_display.c

@@ -8267,7 +8267,9 @@ static void intel_setup_outputs(struct drm_device *dev)
 		I915_WRITE(PFIT_CONTROL, 0);
 	}
 
-	intel_crt_init(dev);
+	if (!(IS_HASWELL(dev) &&
+	      (I915_READ(DDI_BUF_CTL(PORT_A)) & DDI_A_4_LANES)))
+		intel_crt_init(dev);
 
 	if (IS_HASWELL(dev)) {
 		int found;