drm/i915: Preserve the FDI line reversal override bit on CPT

The FDI link has supported link reversal to make the PCB layout
engineer's life easier for quite a while and we have always presered
this bit as we programmed FDI_RX_CTL with a read/modify/write sequence.

We're trying to take a bit more control over what the BIOS leaves in
various register and with the introduction of DDI, started to program
FDI_RX_CTL fully.

There's a fused bit to indicate DMI link reversal and FDI defaults to
mirroring that configuration. We have a bit to override that behaviour
that we need to preserve from the BIOS.

Signed-off-by: Damien Lespiau <damien.lespiau@intel.com>
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@gmail.com>
Reviewed-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
Cc: stable@vger.kernel.org
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/i915_drv.h

@@ -1040,7 +1040,7 @@ typedef struct drm_i915_private {
 	bool hw_contexts_disabled;
 	uint32_t hw_context_size;
 
-	bool fdi_rx_polarity_reversed;
+	u32 fdi_rx_config;
 
 	struct i915_suspend_saved_registers regfile;
 

drivers/gpu/drm/i915/i915_reg.h

@@ -3911,7 +3911,7 @@
 #define  FDI_10BPC                      (1<<16)
 #define  FDI_6BPC                       (2<<16)
 #define  FDI_12BPC                      (3<<16)
-#define  FDI_LINK_REVERSE_OVERWRITE     (1<<15)
+#define  FDI_RX_LINK_REVERSAL_OVERRIDE  (1<<15)
 #define  FDI_DMI_LINK_REVERSE_MASK      (1<<14)
 #define  FDI_RX_PLL_ENABLE              (1<<13)
 #define  FDI_FS_ERR_CORRECT_ENABLE      (1<<11)

drivers/gpu/drm/i915/intel_crt.c

@@ -801,10 +801,14 @@ void intel_crt_init(struct drm_device *dev)
 	dev_priv->hotplug_supported_mask |= CRT_HOTPLUG_INT_STATUS;
 
 	/*
-	 * TODO: find a proper way to discover whether we need to set the
-	 * polarity reversal bit or not, instead of relying on the BIOS.
+	 * TODO: find a proper way to discover whether we need to set the the
+	 * polarity and link reversal bits or not, instead of relying on the
+	 * BIOS.
 	 */
-	if (HAS_PCH_LPT(dev))
-		dev_priv->fdi_rx_polarity_reversed =
-		     !!(I915_READ(_FDI_RXA_CTL) & FDI_RX_POLARITY_REVERSED_LPT);
+	if (HAS_PCH_LPT(dev)) {
+		u32 fdi_config = FDI_RX_POLARITY_REVERSED_LPT |
+				 FDI_RX_LINK_REVERSAL_OVERRIDE;
+
+		dev_priv->fdi_rx_config = I915_READ(_FDI_RXA_CTL) & fdi_config;
+	}
 }

drivers/gpu/drm/i915/intel_ddi.c

@@ -180,10 +180,8 @@ void hsw_fdi_link_train(struct drm_crtc *crtc)
 				  FDI_RX_TP1_TO_TP2_48 | FDI_RX_FDI_DELAY_90);
 
 	/* Enable the PCH Receiver FDI PLL */
-	rx_ctl_val = FDI_RX_PLL_ENABLE | FDI_RX_ENHANCE_FRAME_ENABLE |
-		     ((intel_crtc->fdi_lanes - 1) << 19);
-	if (dev_priv->fdi_rx_polarity_reversed)
-		rx_ctl_val |= FDI_RX_POLARITY_REVERSED_LPT;
+	rx_ctl_val = dev_priv->fdi_rx_config | FDI_RX_ENHANCE_FRAME_ENABLE |
+		     FDI_RX_PLL_ENABLE | ((intel_crtc->fdi_lanes - 1) << 19);
 	I915_WRITE(_FDI_RXA_CTL, rx_ctl_val);
 	POSTING_READ(_FDI_RXA_CTL);
 	udelay(220);