drm/dp: let drivers specify the name of the I2C-over-AUX adapter

Let the drivers specify the name of the I2C-over-AUX adapter to maintain
backwards compatibility in the sysfs when converting to the new
I2C-over-AUX helper infrastructure.

The i915 driver currently uses DPDDC-A to DPDDC-D as names for the DP
i2c adapters. These names show up in the i2c sysfs name attribute. We'd
like to be able to maintain that when switching over to the new helpers.

Due to i2c device and connector cleanup ordering issues we also recently
made the drm device (instead of connector) the parent of the i2c
adapters:

commit 80f65de3c9b8101c1613fa82df500ba6a099a11c
Author: Imre Deak <imre.deak@intel.com>
Date:   Tue Feb 11 17:12:49 2014 +0200

    drm/i915: dp: fix order of dp aux i2c device cleanup

With the name picked up from the adapter parent using dev_name(), it
would be the same for all i2c adapters with the current I2C-over-AUX
helpers.

Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Reviewed-by: Thierry Reding <treding@nvidia.com>
Acked-by: Dave Airlie <airlied@redhat.com>
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@gmail.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/drm_dp_helper.c

@@ -726,7 +726,8 @@ int drm_dp_aux_register_i2c_bus(struct drm_dp_aux *aux)
 	aux->ddc.dev.parent = aux->dev;
 	aux->ddc.dev.of_node = aux->dev->of_node;
 
-	strncpy(aux->ddc.name, dev_name(aux->dev), sizeof(aux->ddc.name));
+	strlcpy(aux->ddc.name, aux->name ? aux->name : dev_name(aux->dev),
+		sizeof(aux->ddc.name));
 
 	return i2c_add_adapter(&aux->ddc);
 }

include/drm/drm_dp_helper.h

@@ -438,6 +438,9 @@ struct drm_dp_aux_msg {
  * The .dev field should be set to a pointer to the device that implements
  * the AUX channel.
  *
+ * The .name field may be used to specify the name of the I2C adapter. If set to
+ * NULL, dev_name() of .dev will be used.
+ *
  * Drivers provide a hardware-specific implementation of how transactions
  * are executed via the .transfer() function. A pointer to a drm_dp_aux_msg
  * structure describing the transaction is passed into this function. Upon
@@ -455,6 +458,7 @@ struct drm_dp_aux_msg {
  * should call drm_dp_aux_unregister_i2c_bus() to remove the I2C adapter.
  */
 struct drm_dp_aux {
+	const char *name;
 	struct i2c_adapter ddc;
 	struct device *dev;