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 Math functions
>> 7 ~~~~~~~~~~~~~~
>> 8
>> 9 Provide some commonly-used math functions, usually required in order to
>> 10 estimate signal strength and signal to noise measurements in dB.
>> 11
>> 12 .. kernel-doc:: include/media/dvb_math.h
>> 13
>> 14
6 DVB devices 15 DVB devices
7 ~~~~~~~~~~~ 16 ~~~~~~~~~~~
8 17
9 Those functions are responsible for handling t 18 Those functions are responsible for handling the DVB device nodes.
10 19
11 .. kernel-doc:: include/media/dvbdev.h 20 .. kernel-doc:: include/media/dvbdev.h
12 21
13 Digital TV Ring buffer 22 Digital TV Ring buffer
14 ~~~~~~~~~~~~~~~~~~~~~~ 23 ~~~~~~~~~~~~~~~~~~~~~~
15 24
16 Those routines implement ring buffers used to 25 Those routines implement ring buffers used to handle digital TV data and
17 copy it from/to userspace. 26 copy it from/to userspace.
18 27
19 .. note:: 28 .. note::
20 29
21 1) For performance reasons read and write ro 30 1) For performance reasons read and write routines don't check buffer sizes
22 and/or number of bytes free/available. Th 31 and/or number of bytes free/available. This has to be done before these
23 routines are called. For example: 32 routines are called. For example:
24 33
25 .. code-block:: c 34 .. code-block:: c
26 35
27 /* write @buflen: bytes */ 36 /* write @buflen: bytes */
28 free = dvb_ringbuffer_free(rbuf); 37 free = dvb_ringbuffer_free(rbuf);
29 if (free >= buflen) 38 if (free >= buflen)
30 count = dvb_ringbuffer_write(r 39 count = dvb_ringbuffer_write(rbuf, buffer, buflen);
31 else 40 else
32 /* do something */ 41 /* do something */
33 42
34 /* read min. 1000, max. @bufsize: byte 43 /* read min. 1000, max. @bufsize: bytes */
35 avail = dvb_ringbuffer_avail(rbuf); 44 avail = dvb_ringbuffer_avail(rbuf);
36 if (avail >= 1000) 45 if (avail >= 1000)
37 count = dvb_ringbuffer_read(rb 46 count = dvb_ringbuffer_read(rbuf, buffer, min(avail, bufsize));
38 else 47 else
39 /* do something */ 48 /* do something */
40 49
41 2) If there is exactly one reader and one wr 50 2) If there is exactly one reader and one writer, there is no need
42 to lock read or write operations. 51 to lock read or write operations.
43 Two or more readers must be locked agains 52 Two or more readers must be locked against each other.
44 Flushing the buffer counts as a read oper 53 Flushing the buffer counts as a read operation.
45 Resetting the buffer counts as a read and 54 Resetting the buffer counts as a read and write operation.
46 Two or more writers must be locked agains 55 Two or more writers must be locked against each other.
47 56
48 .. kernel-doc:: include/media/dvb_ringbuffer.h 57 .. kernel-doc:: include/media/dvb_ringbuffer.h
49 58
50 Digital TV VB2 handler 59 Digital TV VB2 handler
51 ~~~~~~~~~~~~~~~~~~~~~~ 60 ~~~~~~~~~~~~~~~~~~~~~~
52 61
53 .. kernel-doc:: include/media/dvb_vb2.h 62 .. kernel-doc:: include/media/dvb_vb2.h
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