media: docs: move uAPI book to userspace-api/media

Since 2017, there is an space reserved for userspace API,
created by changeset 1d596dee3862 ("docs: Create a user-space API guide").

As the media subsystem was one of the first subsystems to use
Sphinx, until this patch, we were keeping things on a separate
place.

Let's just use the new location, as having all uAPI altogether
will likely make things easier for developers.

Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>

1 files changed, 126 insertions, 0 deletions

diff --git a/Documentation/userspace-api/media/dvb/dvb-frontend-parameters.rst b/Documentation/userspace-api/media/dvb/dvb-frontend-parameters.rst
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+.. Permission is granted to copy, distribute and/or modify this
+.. document under the terms of the GNU Free Documentation License,
+.. Version 1.1 or any later version published by the Free Software
+.. Foundation, with no Invariant Sections, no Front-Cover Texts
+.. and no Back-Cover Texts. A copy of the license is included at
+.. Documentation/userspace-api/media/fdl-appendix.rst.
+..
+.. TODO: replace it to GFDL-1.1-or-later WITH no-invariant-sections
+
+.. c:type:: dvb_frontend_parameters
+
+*******************
+frontend parameters
+*******************
+
+The kind of parameters passed to the frontend device for tuning depend
+on the kind of hardware you are using.
+
+The struct ``dvb_frontend_parameters`` uses a union with specific
+per-system parameters. However, as newer delivery systems required more
+data, the structure size weren't enough to fit, and just extending its
+size would break the existing applications. So, those parameters were
+replaced by the usage of
+:ref:`FE_GET_PROPERTY/FE_SET_PROPERTY <FE_GET_PROPERTY>`
+ioctl's. The new API is flexible enough to add new parameters to
+existing delivery systems, and to add newer delivery systems.
+
+So, newer applications should use
+:ref:`FE_GET_PROPERTY/FE_SET_PROPERTY <FE_GET_PROPERTY>`
+instead, in order to be able to support the newer System Delivery like
+DVB-S2, DVB-T2, DVB-C2, ISDB, etc.
+
+All kinds of parameters are combined as a union in the
+``dvb_frontend_parameters`` structure:
+
+
+.. code-block:: c
+
+    struct dvb_frontend_parameters {
+	uint32_t frequency;     /* (absolute) frequency in Hz for QAM/OFDM */
+		    /* intermediate frequency in kHz for QPSK */
+	fe_spectral_inversion_t inversion;
+	union {
+	    struct dvb_qpsk_parameters qpsk;
+	    struct dvb_qam_parameters  qam;
+	    struct dvb_ofdm_parameters ofdm;
+	    struct dvb_vsb_parameters  vsb;
+	} u;
+    };
+
+In the case of QPSK frontends the ``frequency`` field specifies the
+intermediate frequency, i.e. the offset which is effectively added to
+the local oscillator frequency (LOF) of the LNB. The intermediate
+frequency has to be specified in units of kHz. For QAM and OFDM
+frontends the ``frequency`` specifies the absolute frequency and is
+given in Hz.
+
+
+.. c:type:: dvb_qpsk_parameters
+
+QPSK parameters
+===============
+
+For satellite QPSK frontends you have to use the ``dvb_qpsk_parameters``
+structure:
+
+
+.. code-block:: c
+
+     struct dvb_qpsk_parameters {
+	 uint32_t        symbol_rate;  /* symbol rate in Symbols per second */
+	 fe_code_rate_t  fec_inner;    /* forward error correction (see above) */
+     };
+
+
+.. c:type:: dvb_qam_parameters
+
+QAM parameters
+==============
+
+for cable QAM frontend you use the ``dvb_qam_parameters`` structure:
+
+
+.. code-block:: c
+
+     struct dvb_qam_parameters {
+	 uint32_t         symbol_rate; /* symbol rate in Symbols per second */
+	 fe_code_rate_t   fec_inner;   /* forward error correction (see above) */
+	 fe_modulation_t  modulation;  /* modulation type (see above) */
+     };
+
+
+.. c:type:: dvb_vsb_parameters
+
+VSB parameters
+==============
+
+ATSC frontends are supported by the ``dvb_vsb_parameters`` structure:
+
+
+.. code-block:: c
+
+    struct dvb_vsb_parameters {
+	fe_modulation_t modulation; /* modulation type (see above) */
+    };
+
+
+.. c:type:: dvb_ofdm_parameters
+
+OFDM parameters
+===============
+
+DVB-T frontends are supported by the ``dvb_ofdm_parameters`` structure:
+
+
+.. code-block:: c
+
+     struct dvb_ofdm_parameters {
+	 fe_bandwidth_t      bandwidth;
+	 fe_code_rate_t      code_rate_HP;  /* high priority stream code rate */
+	 fe_code_rate_t      code_rate_LP;  /* low priority stream code rate */
+	 fe_modulation_t     constellation; /* modulation type (see above) */
+	 fe_transmit_mode_t  transmission_mode;
+	 fe_guard_interval_t guard_interval;
+	 fe_hierarchy_t      hierarchy_information;
+     };