[PATCHv16 07/13] cec.txt: add CEC framework documentation

Thu Jun 16 20:12:44 UTC 2016

Em Fri, 29 Apr 2016 15:52:22 +0200
Hans Verkuil <hverkuil at xs4all.nl> escreveu:

> From: Hans Verkuil <hansverk at cisco.com>
> 
> Document the new HDMI CEC framework.

As we'll be moving documentation to Sphinx/Rst, it would be good if
you could make it work fine with sphinx, as this will likely be needed
for Kernel 4.9. Right now it most works, although several warnings are
produced: 

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> 
> Signed-off-by: Hans Verkuil <hansverk at cisco.com>
> [k.debski at samsung.com: add DocBook documentation by Hans Verkuil, with
> Signed-off-by: Kamil Debski <kamil at wypas.org>
> Signed-off-by: Hans Verkuil <hans.verkuil at cisco.com>
> ---
>  Documentation/cec.txt | 267 ++++++++++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 267 insertions(+)
>  create mode 100644 Documentation/cec.txt
> 
> diff --git a/Documentation/cec.txt b/Documentation/cec.txt
> new file mode 100644
> index 0000000..75155fe
> --- /dev/null
> +++ b/Documentation/cec.txt
> @@ -0,0 +1,267 @@
> +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.

Thanks,
Mauro