drm/i915: Enable DVO 2x clock around DVO encoder init

ns2501 requires the DVO 2x clock before it will respond to i2c access,
so make sure the clock is enabled when we try to initialize the encoder.

Fixes the display getting lost on module reload on my Fujitsu/Siemens
Lifebook S6010.
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/intel_dvo.c

@@ -495,6 +495,8 @@ void intel_dvo_init(struct drm_device *dev)
 		struct i2c_adapter *i2c;
 		int gpio;
 		bool dvoinit;
+		enum pipe pipe;
+		uint32_t dpll[2];
 
 		/* Allow the I2C driver info to specify the GPIO to be used in
 		 * special cases, but otherwise default to what's defined
@@ -520,8 +522,23 @@ void intel_dvo_init(struct drm_device *dev)
 		 */
 		intel_gmbus_force_bit(i2c, true);
 
+		/* ns2501 requires the DVO 2x clock before it will
+		 * respond to i2c accesses, so make sure we have
+		 * have the clock enabled before we attempt to
+		 * initialize the device.
+		 */
+		for_each_pipe(dev_priv, pipe) {
+			dpll[pipe] = I915_READ(DPLL(pipe));
+			I915_WRITE(DPLL(pipe), dpll[pipe] | DPLL_DVO_2X_MODE);
+		}
+
 		dvoinit = dvo->dev_ops->init(&intel_dvo->dev, i2c);
 
+		/* restore the DVO 2x clock state to original */
+		for_each_pipe(dev_priv, pipe) {
+			I915_WRITE(DPLL(pipe), dpll[pipe]);
+		}
+
 		intel_gmbus_force_bit(i2c, false);
 
 		if (!dvoinit)