drm/i915: apply timing generator bug workaround on CPT and PPT

On CougarPoint and PantherPoint PCH chips, the timing generator may fail
to start after DP training completes.  This is due to a bug in the
FDI autotraining detect logic (which will stall the timing generator and
re-enable it once training completes), so disable it to avoid silent DP
mode setting failures.
Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>
Signed-off-by: Keith Packard <keithp@keithp.com>

drivers/gpu/drm/i915/i915_reg.h

@@ -3072,6 +3072,11 @@
 #define  TRANS_6BPC             (2<<5)
 #define  TRANS_12BPC            (3<<5)
 
+#define _TRANSA_CHICKEN2	 0xf0064
+#define _TRANSB_CHICKEN2	 0xf1064
+#define TRANS_CHICKEN2(pipe) _PIPE(pipe, _TRANSA_CHICKEN2, _TRANSB_CHICKEN2)
+#define   TRANS_AUTOTRAIN_GEN_STALL_DIS	(1<<31)
+
 #define SOUTH_CHICKEN2		0xc2004
 #define  DPLS_EDP_PPS_FIX_DIS	(1<<0)
 

drivers/gpu/drm/i915/intel_display.c

@@ -7524,6 +7524,7 @@ static void ibx_init_clock_gating(struct drm_device *dev)
 static void cpt_init_clock_gating(struct drm_device *dev)
 {
 	struct drm_i915_private *dev_priv = dev->dev_private;
+	int pipe;
 
 	/*
 	 * On Ibex Peak and Cougar Point, we need to disable clock
@@ -7533,6 +7534,9 @@ static void cpt_init_clock_gating(struct drm_device *dev)
 	I915_WRITE(SOUTH_DSPCLK_GATE_D, PCH_DPLSUNIT_CLOCK_GATE_DISABLE);
 	I915_WRITE(SOUTH_CHICKEN2, I915_READ(SOUTH_CHICKEN2) |
 		   DPLS_EDP_PPS_FIX_DIS);
+	/* Without this, mode sets may fail silently on FDI */
+	for_each_pipe(pipe)
+		I915_WRITE(TRANS_CHICKEN2(pipe), TRANS_AUTOTRAIN_GEN_STALL_DIS);
 }
 
 static void ironlake_teardown_rc6(struct drm_device *dev)