drm/i915/i2c: Track users of GMBUS force-bit

This fixes a regression for SDVO from

commit fbfcc4f3
Author: Jani Nikula <jani.nikula@intel.com>
Date:   Mon Oct 22 16:12:18 2012 +0300

    drm/i915/sdvo: restore i2c adapter config on intel_sdvo_init() failures

As SDVOB and SDVOC are multiplexed on the same pin, if a chipset does
not have the second SDVO encoder, it will then remove the force-bit
setting on the common i2c adapter during teardown. All subsequent
attempts of trying to use GMBUS with SDVOB then fail.
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Jani Nikula <jani.nikula@intel.com>
Cc: Mika Kuoppala <mika.kuoppala@intel.com>
[danvet: fixup inversion in the debug printout, noticed by Jani
Nikulai.]
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/i915_drv.h

@@ -390,7 +390,7 @@ struct intel_fbc_work;
 
 struct intel_gmbus {
 	struct i2c_adapter adapter;
-	bool force_bit;
+	u32 force_bit;
 	u32 reg0;
 	u32 gpio_reg;
 	struct i2c_algo_bit_data bit_algo;

drivers/gpu/drm/i915/intel_i2c.c

@@ -432,7 +432,7 @@ gmbus_xfer(struct i2c_adapter *adapter,
 	I915_WRITE(GMBUS0 + reg_offset, 0);
 
 	/* Hardware may not support GMBUS over these pins? Try GPIO bitbanging instead. */
-	bus->force_bit = true;
+	bus->force_bit = 1;
 	ret = i2c_bit_algo.master_xfer(adapter, msgs, num);
 
 out:
@@ -491,7 +491,7 @@ int intel_setup_gmbus(struct drm_device *dev)
 
 		/* gmbus seems to be broken on i830 */
 		if (IS_I830(dev))
-			bus->force_bit = true;
+			bus->force_bit = 1;
 
 		intel_gpio_setup(bus, port);
 
@@ -532,7 +532,10 @@ void intel_gmbus_force_bit(struct i2c_adapter *adapter, bool force_bit)
 {
 	struct intel_gmbus *bus = to_intel_gmbus(adapter);
 
-	bus->force_bit = force_bit;
+	bus->force_bit += force_bit ? 1 : -1;
+	DRM_DEBUG_KMS("%sabling bit-banging on %s. force bit now %d\n",
+		      force_bit ? "en" : "dis", adapter->name,
+		      bus->force_bit);
 }
 
 void intel_teardown_gmbus(struct drm_device *dev)