drm/i915: Fix DDC on some systems by clearing BIOS GMBUS setup.

This is a sync of a fix I made in the old UMS code.  If the BIOS uses
the GMBUS and doesn't clear that setup, then our bit-banging I2C can
fail, leading to monitors not being detected.
Signed-off-by: NEric Anholt <eric@anholt.net>

drivers/gpu/drm/i915/i915_reg.h

@@ -414,6 +414,13 @@
 # define GPIO_DATA_VAL_IN		(1 << 12)
 # define GPIO_DATA_PULLUP_DISABLE	(1 << 13)
 
+#define GMBUS0			0x5100
+#define GMBUS1			0x5104
+#define GMBUS2			0x5108
+#define GMBUS3			0x510c
+#define GMBUS4			0x5110
+#define GMBUS5			0x5120
+
 /*
  * Clock control & power management
  */
@@ -2166,6 +2173,13 @@
 #define PCH_GPIOE               0xc5020
 #define PCH_GPIOF               0xc5024
 
+#define PCH_GMBUS0		0xc5100
+#define PCH_GMBUS1		0xc5104
+#define PCH_GMBUS2		0xc5108
+#define PCH_GMBUS3		0xc510c
+#define PCH_GMBUS4		0xc5110
+#define PCH_GMBUS5		0xc5120
+
 #define PCH_DPLL_A              0xc6014
 #define PCH_DPLL_B              0xc6018
 

drivers/gpu/drm/i915/i915_suspend.c

@@ -27,7 +27,7 @@
 #include "drmP.h"
 #include "drm.h"
 #include "i915_drm.h"
-#include "i915_drv.h"
+#include "intel_drv.h"
 
 static bool i915_pipe_enabled(struct drm_device *dev, enum pipe pipe)
 {
@@ -816,6 +816,9 @@ int i915_restore_state(struct drm_device *dev)
 	for (i = 0; i < 3; i++)
 		I915_WRITE(SWF30 + (i << 2), dev_priv->saveSWF2[i]);
 
+	/* I2C state */
+	intel_i2c_reset_gmbus(dev);
+
 	return 0;
 }
 

drivers/gpu/drm/i915/intel_drv.h

@@ -162,6 +162,8 @@ void intel_i2c_destroy(struct i2c_adapter *adapter);
 int intel_ddc_get_modes(struct intel_output *intel_output);
 extern bool intel_ddc_probe(struct intel_output *intel_output);
 void intel_i2c_quirk_set(struct drm_device *dev, bool enable);
+void intel_i2c_reset_gmbus(struct drm_device *dev);
+
 extern void intel_crt_init(struct drm_device *dev);
 extern void intel_hdmi_init(struct drm_device *dev, int sdvox_reg);
 extern bool intel_sdvo_init(struct drm_device *dev, int output_device);

drivers/gpu/drm/i915/intel_i2c.c

@@ -118,6 +118,23 @@ static void set_data(void *data, int state_high)
 	udelay(I2C_RISEFALL_TIME); /* wait for the line to change state */
 }
 
+/* Clears the GMBUS setup.  Our driver doesn't make use of the GMBUS I2C
+ * engine, but if the BIOS leaves it enabled, then that can break our use
+ * of the bit-banging I2C interfaces.  This is notably the case with the
+ * Mac Mini in EFI mode.
+ */
+void
+intel_i2c_reset_gmbus(struct drm_device *dev)
+{
+	struct drm_i915_private *dev_priv = dev->dev_private;
+
+	if (IS_IGDNG(dev)) {
+		I915_WRITE(PCH_GMBUS0, 0);
+	} else {
+		I915_WRITE(GMBUS0, 0);
+	}
+}
+
 /**
  * intel_i2c_create - instantiate an Intel i2c bus using the specified GPIO reg
  * @dev: DRM device
@@ -168,6 +185,8 @@ struct i2c_adapter *intel_i2c_create(struct drm_device *dev, const u32 reg,
 	if(i2c_bit_add_bus(&chan->adapter))
 		goto out_free;
 
+	intel_i2c_reset_gmbus(dev);
+
 	/* JJJ:  raise SCL and SDA? */
 	intel_i2c_quirk_set(dev, true);
 	set_data(chan, 1);