268 строки
10 KiB
Plaintext
268 строки
10 KiB
Plaintext
CEC Kernel Support
|
|
==================
|
|
|
|
The CEC framework provides a unified kernel interface for use with HDMI CEC
|
|
hardware. It is designed to handle a multiple types of hardware (receivers,
|
|
transmitters, USB dongles). The framework also gives the option to decide
|
|
what to do in the kernel driver and what should be handled by userspace
|
|
applications. In addition it integrates the remote control passthrough
|
|
feature into the kernel's remote control framework.
|
|
|
|
|
|
The CEC Protocol
|
|
----------------
|
|
|
|
The CEC protocol enables consumer electronic devices to communicate with each
|
|
other through the HDMI connection. The protocol uses logical addresses in the
|
|
communication. The logical address is strictly connected with the functionality
|
|
provided by the device. The TV acting as the communication hub is always
|
|
assigned address 0. The physical address is determined by the physical
|
|
connection between devices.
|
|
|
|
The CEC framework described here is up to date with the CEC 2.0 specification.
|
|
It is documented in the HDMI 1.4 specification with the new 2.0 bits documented
|
|
in the HDMI 2.0 specification. But for most of the features the freely available
|
|
HDMI 1.3a specification is sufficient:
|
|
|
|
http://www.microprocessor.org/HDMISpecification13a.pdf
|
|
|
|
|
|
The Kernel Interface
|
|
====================
|
|
|
|
CEC Adapter
|
|
-----------
|
|
|
|
The struct cec_adapter represents the CEC adapter hardware. It is created by
|
|
calling cec_allocate_adapter() and deleted by calling cec_delete_adapter():
|
|
|
|
struct cec_adapter *cec_allocate_adapter(const struct cec_adap_ops *ops,
|
|
void *priv, const char *name, u32 caps, u8 available_las,
|
|
struct device *parent);
|
|
void cec_delete_adapter(struct cec_adapter *adap);
|
|
|
|
To create an adapter you need to pass the following information:
|
|
|
|
ops: adapter operations which are called by the CEC framework and that you
|
|
have to implement.
|
|
|
|
priv: will be stored in adap->priv and can be used by the adapter ops.
|
|
|
|
name: the name of the CEC adapter. Note: this name will be copied.
|
|
|
|
caps: capabilities of the CEC adapter. These capabilities determine the
|
|
capabilities of the hardware and which parts are to be handled
|
|
by userspace and which parts are handled by kernelspace. The
|
|
capabilities are returned by CEC_ADAP_G_CAPS.
|
|
|
|
available_las: the number of simultaneous logical addresses that this
|
|
adapter can handle. Must be 1 <= available_las <= CEC_MAX_LOG_ADDRS.
|
|
|
|
parent: the parent device.
|
|
|
|
|
|
To register the /dev/cecX device node and the remote control device (if
|
|
CEC_CAP_RC is set) you call:
|
|
|
|
int cec_register_adapter(struct cec_adapter *adap);
|
|
|
|
To unregister the devices call:
|
|
|
|
void cec_unregister_adapter(struct cec_adapter *adap);
|
|
|
|
Note: if cec_register_adapter() fails, then call cec_delete_adapter() to
|
|
clean up. But if cec_register_adapter() succeeded, then only call
|
|
cec_unregister_adapter() to clean up, never cec_delete_adapter(). The
|
|
unregister function will delete the adapter automatically once the last user
|
|
of that /dev/cecX device has closed its file handle.
|
|
|
|
|
|
Implementing the Low-Level CEC Adapter
|
|
--------------------------------------
|
|
|
|
The following low-level adapter operations have to be implemented in
|
|
your driver:
|
|
|
|
struct cec_adap_ops {
|
|
/* Low-level callbacks */
|
|
int (*adap_enable)(struct cec_adapter *adap, bool enable);
|
|
int (*adap_monitor_all_enable)(struct cec_adapter *adap, bool enable);
|
|
int (*adap_log_addr)(struct cec_adapter *adap, u8 logical_addr);
|
|
int (*adap_transmit)(struct cec_adapter *adap, u8 attempts,
|
|
u32 signal_free_time, struct cec_msg *msg);
|
|
void (*adap_log_status)(struct cec_adapter *adap);
|
|
|
|
/* High-level callbacks */
|
|
...
|
|
};
|
|
|
|
The three low-level ops deal with various aspects of controlling the CEC adapter
|
|
hardware:
|
|
|
|
|
|
To enable/disable the hardware:
|
|
|
|
int (*adap_enable)(struct cec_adapter *adap, bool enable);
|
|
|
|
This callback enables or disables the CEC hardware. Enabling the CEC hardware
|
|
means powering it up in a state where no logical addresses are claimed. This
|
|
op assumes that the physical address (adap->phys_addr) is valid when enable is
|
|
true and will not change while the CEC adapter remains enabled. The initial
|
|
state of the CEC adapter after calling cec_allocate_adapter() is disabled.
|
|
|
|
Note that adap_enable must return 0 if enable is false.
|
|
|
|
|
|
To enable/disable the 'monitor all' mode:
|
|
|
|
int (*adap_monitor_all_enable)(struct cec_adapter *adap, bool enable);
|
|
|
|
If enabled, then the adapter should be put in a mode to also monitor messages
|
|
that not for us. Not all hardware supports this and this function is only
|
|
called if the CEC_CAP_MONITOR_ALL capability is set. This callback is optional
|
|
(some hardware may always be in 'monitor all' mode).
|
|
|
|
Note that adap_monitor_all_enable must return 0 if enable is false.
|
|
|
|
|
|
To program a new logical address:
|
|
|
|
int (*adap_log_addr)(struct cec_adapter *adap, u8 logical_addr);
|
|
|
|
If logical_addr == CEC_LOG_ADDR_INVALID then all programmed logical addresses
|
|
are to be erased. Otherwise the given logical address should be programmed.
|
|
If the maximum number of available logical addresses is exceeded, then it
|
|
should return -ENXIO. Once a logical address is programmed the CEC hardware
|
|
can receive directed messages to that address.
|
|
|
|
Note that adap_log_addr must return 0 if logical_addr is CEC_LOG_ADDR_INVALID.
|
|
|
|
|
|
To transmit a new message:
|
|
|
|
int (*adap_transmit)(struct cec_adapter *adap, u8 attempts,
|
|
u32 signal_free_time, struct cec_msg *msg);
|
|
|
|
This transmits a new message. The attempts argument is the suggested number of
|
|
attempts for the transmit.
|
|
|
|
The signal_free_time is the number of data bit periods that the adapter should
|
|
wait when the line is free before attempting to send a message. This value
|
|
depends on whether this transmit is a retry, a message from a new initiator or
|
|
a new message for the same initiator. Most hardware will handle this
|
|
automatically, but in some cases this information is needed.
|
|
|
|
The CEC_FREE_TIME_TO_USEC macro can be used to convert signal_free_time to
|
|
microseconds (one data bit period is 2.4 ms).
|
|
|
|
|
|
To log the current CEC hardware status:
|
|
|
|
void (*adap_status)(struct cec_adapter *adap, struct seq_file *file);
|
|
|
|
This optional callback can be used to show the status of the CEC hardware.
|
|
The status is available through debugfs: cat /sys/kernel/debug/cec/cecX/status
|
|
|
|
|
|
Your adapter driver will also have to react to events (typically interrupt
|
|
driven) by calling into the framework in the following situations:
|
|
|
|
When a transmit finished (successfully or otherwise):
|
|
|
|
void cec_transmit_done(struct cec_adapter *adap, u8 status, u8 arb_lost_cnt,
|
|
u8 nack_cnt, u8 low_drive_cnt, u8 error_cnt);
|
|
|
|
The status can be one of:
|
|
|
|
CEC_TX_STATUS_OK: the transmit was successful.
|
|
CEC_TX_STATUS_ARB_LOST: arbitration was lost: another CEC initiator
|
|
took control of the CEC line and you lost the arbitration.
|
|
CEC_TX_STATUS_NACK: the message was nacked (for a directed message) or
|
|
acked (for a broadcast message). A retransmission is needed.
|
|
CEC_TX_STATUS_LOW_DRIVE: low drive was detected on the CEC bus. This
|
|
indicates that a follower detected an error on the bus and requested a
|
|
retransmission.
|
|
CEC_TX_STATUS_ERROR: some unspecified error occurred: this can be one of
|
|
the previous two if the hardware cannot differentiate or something else
|
|
entirely.
|
|
CEC_TX_STATUS_MAX_RETRIES: could not transmit the message after
|
|
trying multiple times. Should only be set by the driver if it has hardware
|
|
support for retrying messages. If set, then the framework assumes that it
|
|
doesn't have to make another attempt to transmit the message since the
|
|
hardware did that already.
|
|
|
|
The *_cnt arguments are the number of error conditions that were seen.
|
|
This may be 0 if no information is available. Drivers that do not support
|
|
hardware retry can just set the counter corresponding to the transmit error
|
|
to 1, if the hardware does support retry then either set these counters to
|
|
0 if the hardware provides no feedback of which errors occurred and how many
|
|
times, or fill in the correct values as reported by the hardware.
|
|
|
|
When a CEC message was received:
|
|
|
|
void cec_received_msg(struct cec_adapter *adap, struct cec_msg *msg);
|
|
|
|
Speaks for itself.
|
|
|
|
Implementing the High-Level CEC Adapter
|
|
---------------------------------------
|
|
|
|
The low-level operations drive the hardware, the high-level operations are
|
|
CEC protocol driven. The following high-level callbacks are available:
|
|
|
|
struct cec_adap_ops {
|
|
/* Low-level callbacks */
|
|
...
|
|
|
|
/* High-level CEC message callback */
|
|
int (*received)(struct cec_adapter *adap, struct cec_msg *msg);
|
|
};
|
|
|
|
The received() callback allows the driver to optionally handle a newly
|
|
received CEC message
|
|
|
|
int (*received)(struct cec_adapter *adap, struct cec_msg *msg);
|
|
|
|
If the driver wants to process a CEC message, then it can implement this
|
|
callback. If it doesn't want to handle this message, then it should return
|
|
-ENOMSG, otherwise the CEC framework assumes it processed this message and
|
|
it will not no anything with it.
|
|
|
|
|
|
CEC framework functions
|
|
-----------------------
|
|
|
|
CEC Adapter drivers can call the following CEC framework functions:
|
|
|
|
int cec_transmit_msg(struct cec_adapter *adap, struct cec_msg *msg,
|
|
bool block);
|
|
|
|
Transmit a CEC message. If block is true, then wait until the message has been
|
|
transmitted, otherwise just queue it and return.
|
|
|
|
void cec_s_phys_addr(struct cec_adapter *adap, u16 phys_addr, bool block);
|
|
|
|
Change the physical address. This function will set adap->phys_addr and
|
|
send an event if it has changed. If cec_s_log_addrs() has been called and
|
|
the physical address has become valid, then the CEC framework will start
|
|
claiming the logical addresses. If block is true, then this function won't
|
|
return until this process has finished.
|
|
|
|
When the physical address is set to a valid value the CEC adapter will
|
|
be enabled (see the adap_enable op). When it is set to CEC_PHYS_ADDR_INVALID,
|
|
then the CEC adapter will be disabled. If you change a valid physical address
|
|
to another valid physical address, then this function will first set the
|
|
address to CEC_PHYS_ADDR_INVALID before enabling the new physical address.
|
|
|
|
int cec_s_log_addrs(struct cec_adapter *adap,
|
|
struct cec_log_addrs *log_addrs, bool block);
|
|
|
|
Claim the CEC logical addresses. Should never be called if CEC_CAP_LOG_ADDRS
|
|
is set. If block is true, then wait until the logical addresses have been
|
|
claimed, otherwise just queue it and return. To unconfigure all logical
|
|
addresses call this function with log_addrs set to NULL or with
|
|
log_addrs->num_log_addrs set to 0. The block argument is ignored when
|
|
unconfiguring. This function will just return if the physical address is
|
|
invalid. Once the physical address becomes valid, then the framework will
|
|
attempt to claim these logical addresses.
|