xref: /kernel/linux/linux-6.6/Documentation/driver-api/media/drivers/pvrusb2.rst

.. SPDX-License-Identifier: GPL-2.0

The pvrusb2 driver
==================

Author: Mike Isely <isely@pobox.com>

Background
----------

This driver is intended for the "Hauppauge WinTV PVR USB 2.0", which
is a USB 2.0 hosted TV Tuner.  This driver is a work in progress.
Its history started with the reverse-engineering effort by Björn
Danielsson <pvrusb2@dax.nu> whose web page can be found here:
http://pvrusb2.dax.nu/

From there Aurelien Alleaume <slts@free.fr> began an effort to
create a video4linux compatible driver.  I began with Aurelien's
last known snapshot and evolved the driver to the state it is in
here.

More information on this driver can be found at:
https://www.isely.net/pvrusb2.html


This driver has a strong separation of layers.  They are very
roughly:

1. Low level wire-protocol implementation with the device.

2. I2C adaptor implementation and corresponding I2C client drivers
   implemented elsewhere in V4L.

3. High level hardware driver implementation which coordinates all
   activities that ensure correct operation of the device.

4. A "context" layer which manages instancing of driver, setup,
   tear-down, arbitration, and interaction with high level
   interfaces appropriately as devices are hotplugged in the
   system.

5. High level interfaces which glue the driver to various published
   Linux APIs (V4L, sysfs, maybe DVB in the future).

The most important shearing layer is between the top 2 layers.  A
lot of work went into the driver to ensure that any kind of
conceivable API can be laid on top of the core driver.  (Yes, the
driver internally leverages V4L to do its work but that really has
nothing to do with the API published by the driver to the outside
world.)  The architecture allows for different APIs to
simultaneously access the driver.  I have a strong sense of fairness
about APIs and also feel that it is a good design principle to keep
implementation and interface isolated from each other.  Thus while
right now the V4L high level interface is the most complete, the
sysfs high level interface will work equally well for similar
functions, and there's no reason I see right now why it shouldn't be
possible to produce a DVB high level interface that can sit right
alongside V4L.

Building
--------

To build these modules essentially amounts to just running "Make",
but you need the kernel source tree nearby and you will likely also
want to set a few controlling environment variables first in order
to link things up with that source tree.  Please see the Makefile
here for comments that explain how to do that.

Source file list / functional overview
--------------------------------------

(Note: The term "module" used below generally refers to loosely
defined functional units within the pvrusb2 driver and bears no
relation to the Linux kernel's concept of a loadable module.)

pvrusb2-audio.[ch] - This is glue logic that resides between this
    driver and the msp3400.ko I2C client driver (which is found
    elsewhere in V4L).

pvrusb2-context.[ch] - This module implements the context for an
    instance of the driver.  Everything else eventually ties back to
    or is otherwise instanced within the data structures implemented
    here.  Hotplugging is ultimately coordinated here.  All high level
    interfaces tie into the driver through this module.  This module
    helps arbitrate each interface's access to the actual driver core,
    and is designed to allow concurrent access through multiple
    instances of multiple interfaces (thus you can for example change
    the tuner's frequency through sysfs while simultaneously streaming
    video through V4L out to an instance of mplayer).

pvrusb2-debug.h - This header defines a printk() wrapper and a mask
    of debugging bit definitions for the various kinds of debug
    messages that can be enabled within the driver.

pvrusb2-debugifc.[ch] - This module implements a crude command line
    oriented debug interface into the driver.  Aside from being part
    of the process for implementing manual firmware extraction (see
    the pvrusb2 web site mentioned earlier), probably I'm the only one
    who has ever used this.  It is mainly a debugging aid.

pvrusb2-eeprom.[ch] - This is glue logic that resides between this
    driver the tveeprom.ko module, which is itself implemented
    elsewhere in V4L.

pvrusb2-encoder.[ch] - This module implements all protocol needed to
    interact with the Conexant mpeg2 encoder chip within the pvrusb2
    device.  It is a crude echo of corresponding logic in ivtv,
    however the design goals (strict isolation) and physical layer
    (proxy through USB instead of PCI) are enough different that this
    implementation had to be completely different.

pvrusb2-hdw-internal.h - This header defines the core data structure
    in the driver used to track ALL internal state related to control
    of the hardware.  Nobody outside of the core hardware-handling
    modules should have any business using this header.  All external
    access to the driver should be through one of the high level
    interfaces (e.g. V4L, sysfs, etc), and in fact even those high
    level interfaces are restricted to the API defined in
    pvrusb2-hdw.h and NOT this header.

pvrusb2-hdw.h - This header defines the full internal API for
    controlling the hardware.  High level interfaces (e.g. V4L, sysfs)
    will work through here.

pvrusb2-hdw.c - This module implements all the various bits of logic
    that handle overall control of a specific pvrusb2 device.
    (Policy, instantiation, and arbitration of pvrusb2 devices fall
    within the jurisdiction of pvrusb-context not here).

pvrusb2-i2c-chips-\*.c - These modules implement the glue logic to
    tie together and configure various I2C modules as they attach to
    the I2C bus.  There are two versions of this file.  The "v4l2"
    version is intended to be used in-tree alongside V4L, where we
    implement just the logic that makes sense for a pure V4L
    environment.  The "all" version is intended for use outside of
    V4L, where we might encounter other possibly "challenging" modules
    from ivtv or older kernel snapshots (or even the support modules
    in the standalone snapshot).

pvrusb2-i2c-cmd-v4l1.[ch] - This module implements generic V4L1
    compatible commands to the I2C modules.  It is here where state
    changes inside the pvrusb2 driver are translated into V4L1
    commands that are in turn send to the various I2C modules.

pvrusb2-i2c-cmd-v4l2.[ch] - This module implements generic V4L2
    compatible commands to the I2C modules.  It is here where state
    changes inside the pvrusb2 driver are translated into V4L2
    commands that are in turn send to the various I2C modules.

pvrusb2-i2c-core.[ch] - This module provides an implementation of a
    kernel-friendly I2C adaptor driver, through which other external
    I2C client drivers (e.g. msp3400, tuner, lirc) may connect and
    operate corresponding chips within the pvrusb2 device.  It is
    through here that other V4L modules can reach into this driver to
    operate specific pieces (and those modules are in turn driven by
    glue logic which is coordinated by pvrusb2-hdw, doled out by
    pvrusb2-context, and then ultimately made available to users
    through one of the high level interfaces).

pvrusb2-io.[ch] - This module implements a very low level ring of
    transfer buffers, required in order to stream data from the
    device.  This module is *very* low level.  It only operates the
    buffers and makes no attempt to define any policy or mechanism for
    how such buffers might be used.

pvrusb2-ioread.[ch] - This module layers on top of pvrusb2-io.[ch]
    to provide a streaming API usable by a read() system call style of
    I/O.  Right now this is the only layer on top of pvrusb2-io.[ch],
    however the underlying architecture here was intended to allow for
    other styles of I/O to be implemented with additional modules, like
    mmap()'ed buffers or something even more exotic.

pvrusb2-main.c - This is the top level of the driver.  Module level
    and USB core entry points are here.  This is our "main".

pvrusb2-sysfs.[ch] - This is the high level interface which ties the
    pvrusb2 driver into sysfs.  Through this interface you can do
    everything with the driver except actually stream data.

pvrusb2-tuner.[ch] - This is glue logic that resides between this
    driver and the tuner.ko I2C client driver (which is found
    elsewhere in V4L).

pvrusb2-util.h - This header defines some common macros used
    throughout the driver.  These macros are not really specific to
    the driver, but they had to go somewhere.

pvrusb2-v4l2.[ch] - This is the high level interface which ties the
    pvrusb2 driver into video4linux.  It is through here that V4L
    applications can open and operate the driver in the usual V4L
    ways.  Note that **ALL** V4L functionality is published only
    through here and nowhere else.

pvrusb2-video-\*.[ch] - This is glue logic that resides between this
    driver and the saa711x.ko I2C client driver (which is found
    elsewhere in V4L).  Note that saa711x.ko used to be known as
    saa7115.ko in ivtv.  There are two versions of this; one is
    selected depending on the particular saa711[5x].ko that is found.

pvrusb2.h - This header contains compile time tunable parameters
    (and at the moment the driver has very little that needs to be
    tuned).