struct drm_dp

struct drm_dp_aux
Prev	Display Port Helper Functions Reference	Next

Name

struct drm_dp_aux — DisplayPort AUX channel

Synopsis

struct drm_dp_aux {
  const char * name;
  struct i2c_adapter ddc;
  struct device * dev;
  struct mutex hw_mutex;
  ssize_t (* transfer) (struct drm_dp_aux *aux,struct drm_dp_aux_msg *msg);
};

Members

name: user-visible name of this AUX channel and the I2C-over-AUX adapter
ddc: I2C adapter that can be used for I2C-over-AUX communication
dev: pointer to struct device that is the parent for this AUX channel
hw_mutex: internal mutex used for locking transfers
transfer: transfers a message representing a single AUX transaction

Description

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 success, the implementation should return the number of payload bytes that were transferred, or a negative error-code on failure. Helpers propagate errors from the .transfer function, with the exception of the -EBUSY error, which causes a transaction to be retried. On a short, helpers will return -EPROTO to make it simpler to check for failure.

An AUX channel can also be used to transport I2C messages to a sink. A typical application of that is to access an EDID that's present in the sink device. The .transfer function can also be used to execute such transactions. The drm_dp_aux_register_i2c_bus function registers an I2C adapter that can be passed to drm_probe_ddc. Upon removal, drivers should call drm_dp_aux_unregister_i2c_bus to remove the I2C adapter.

Note that the aux helper code assumes that the .transfer function only modifies the reply field of the drm_dp_aux_msg structure. The retry logic and i2c helpers assume this is the case.