1 .. SPDX-License-Identifier: GPL-2.0 1 .. SPDX-License-Identifier: GPL-2.0
2 2
3 Digital TV Common functions 3 Digital TV Common functions
4 --------------------------- 4 ---------------------------
5 5
6 DVB devices 6 DVB devices
7 ~~~~~~~~~~~ 7 ~~~~~~~~~~~
8 8
9 Those functions are responsible for handling t 9 Those functions are responsible for handling the DVB device nodes.
10 10
11 .. kernel-doc:: include/media/dvbdev.h 11 .. kernel-doc:: include/media/dvbdev.h
12 12
13 Digital TV Ring buffer 13 Digital TV Ring buffer
14 ~~~~~~~~~~~~~~~~~~~~~~ 14 ~~~~~~~~~~~~~~~~~~~~~~
15 15
16 Those routines implement ring buffers used to 16 Those routines implement ring buffers used to handle digital TV data and
17 copy it from/to userspace. 17 copy it from/to userspace.
18 18
19 .. note:: 19 .. note::
20 20
21 1) For performance reasons read and write ro 21 1) For performance reasons read and write routines don't check buffer sizes
22 and/or number of bytes free/available. Th 22 and/or number of bytes free/available. This has to be done before these
23 routines are called. For example: 23 routines are called. For example:
24 24
25 .. code-block:: c 25 .. code-block:: c
26 26
27 /* write @buflen: bytes */ 27 /* write @buflen: bytes */
28 free = dvb_ringbuffer_free(rbuf); 28 free = dvb_ringbuffer_free(rbuf);
29 if (free >= buflen) 29 if (free >= buflen)
30 count = dvb_ringbuffer_write(r 30 count = dvb_ringbuffer_write(rbuf, buffer, buflen);
31 else 31 else
32 /* do something */ 32 /* do something */
33 33
34 /* read min. 1000, max. @bufsize: byte 34 /* read min. 1000, max. @bufsize: bytes */
35 avail = dvb_ringbuffer_avail(rbuf); 35 avail = dvb_ringbuffer_avail(rbuf);
36 if (avail >= 1000) 36 if (avail >= 1000)
37 count = dvb_ringbuffer_read(rb 37 count = dvb_ringbuffer_read(rbuf, buffer, min(avail, bufsize));
38 else 38 else
39 /* do something */ 39 /* do something */
40 40
41 2) If there is exactly one reader and one wr 41 2) If there is exactly one reader and one writer, there is no need
42 to lock read or write operations. 42 to lock read or write operations.
43 Two or more readers must be locked agains 43 Two or more readers must be locked against each other.
44 Flushing the buffer counts as a read oper 44 Flushing the buffer counts as a read operation.
45 Resetting the buffer counts as a read and 45 Resetting the buffer counts as a read and write operation.
46 Two or more writers must be locked agains 46 Two or more writers must be locked against each other.
47 47
48 .. kernel-doc:: include/media/dvb_ringbuffer.h 48 .. kernel-doc:: include/media/dvb_ringbuffer.h
49 49
50 Digital TV VB2 handler 50 Digital TV VB2 handler
51 ~~~~~~~~~~~~~~~~~~~~~~ 51 ~~~~~~~~~~~~~~~~~~~~~~
52 52
53 .. kernel-doc:: include/media/dvb_vb2.h 53 .. kernel-doc:: include/media/dvb_vb2.h
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