Adding upstream version 4.19.249.upstream/4.19.249upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 60 insertions, 0 deletions

diff --git a/Documentation/media/kapi/dtv-common.rst b/Documentation/media/kapi/dtv-common.rst
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+Digital TV Common functions
+---------------------------
+
+Math functions
+~~~~~~~~~~~~~~
+
+Provide some commonly-used math functions, usually required in order to
+estimate signal strength and signal to noise measurements in dB.
+
+.. kernel-doc:: include/media/dvb_math.h
+
+
+DVB devices
+~~~~~~~~~~~
+
+Those functions are responsible for handling the DVB device nodes.
+
+.. kernel-doc:: include/media/dvbdev.h
+
+Digital TV Ring buffer
+~~~~~~~~~~~~~~~~~~~~~~
+
+Those routines implement ring buffers used to handle digital TV data and
+copy it from/to userspace.
+
+.. note::
+
+  1) For performance reasons read and write routines don't check buffer sizes
+     and/or number of bytes free/available. This has to be done before these
+     routines are called. For example:
+
+   .. code-block:: c
+
+        /* write @buflen: bytes */
+        free = dvb_ringbuffer_free(rbuf);
+        if (free >= buflen)
+                count = dvb_ringbuffer_write(rbuf, buffer, buflen);
+        else
+                /* do something */
+
+        /* read min. 1000, max. @bufsize: bytes */
+        avail = dvb_ringbuffer_avail(rbuf);
+        if (avail >= 1000)
+                count = dvb_ringbuffer_read(rbuf, buffer, min(avail, bufsize));
+        else
+                /* do something */
+
+  2) If there is exactly one reader and one writer, there is no need
+     to lock read or write operations.
+     Two or more readers must be locked against each other.
+     Flushing the buffer counts as a read operation.
+     Resetting the buffer counts as a read and write operation.
+     Two or more writers must be locked against each other.
+
+.. kernel-doc:: include/media/dvb_ringbuffer.h
+
+Digital TV VB2 handler
+~~~~~~~~~~~~~~~~~~~~~~
+
+.. kernel-doc:: include/media/dvb_vb2.h