/drivers/staging/iio/Documentation/ring.txt

 1Buffer support within IIO
 2
 3This document is intended as a general overview of the functionality
 4a buffer may supply and how it is specified within IIO.  For more
 5specific information on a given buffer implementation, see the
 6comments in the source code.  Note that some drivers allow buffer
 7implementation to be selected at compile time via Kconfig options.
 8
 9A given buffer implementation typically embeds a struct
10iio_ring_buffer and it is a pointer to this that is provided to the
11IIO core. Access to the embedding structure is typically done via
12container_of functions.
13
14struct iio_ring_buffer contains a struct iio_ring_setup_ops *setup_ops
15which in turn contains the 4 function pointers
16(preenable, postenable, predisable and postdisable).
17These are used to perform device specific steps on either side
18of the core changing it's current mode to indicate that the buffer
19is enabled or disabled (along with enabling triggering etc as appropriate).
20
21Also in struct iio_ring_buffer is a struct iio_ring_access_funcs.
22The function pointers within here are used to allow the core to handle
23as much buffer functionality as possible. Note almost all of these
24are optional.
25
26mark_in_use, unmark_in_use
27  Basically indicate that not changes should be made to the buffer state that
28  will effect the form of the data being captures (e.g. scan elements or length)
29
30store_to
31  If possible, push data to the buffer.
32
33read_last
34  If possible, get the most recent scan from the buffer (without removal).
35  This provides polling like functionality whilst the ring buffering is in
36  use without a separate read from the device.
37
38rip_first_n
39  The primary buffer reading function. Note that it may well not return
40  as much data as requested.
41
42mark_param_changed
43  Used to indicate that something has changed. Used in conjunction with
44request_update
45  If parameters have changed that require reinitialization or configuration of
46  the buffer this will trigger it.
47
48get_bytes_per_datum, set_bytes_per_datum
49  Get/set the number of bytes for a complete scan. (All samples + timestamp)
50
51get_length / set_length
52  Get/set the number of complete scans that may be held by the buffer.
53
54is_enabled
55  Query if ring buffer is in use
56enable
57  Start the ring buffer.