358 lines
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ReStructuredText
358 lines
12 KiB
ReStructuredText
.. SPDX-License-Identifier: GPL-2.0
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===================================
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Building support for a media device
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===================================
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The first step is to download the Kernel's source code, either via a
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distribution-specific source file or via the Kernel's main git tree\ [1]_.
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Please notice, however, that, if:
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- you're a braveheart and want to experiment with new stuff;
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- if you want to report a bug;
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- if you're developing new patches
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you should use the main media development tree ``master`` branch:
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https://git.linuxtv.org/media_tree.git/
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In this case, you may find some useful information at the
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`LinuxTv wiki pages <https://linuxtv.org/wiki>`_:
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https://linuxtv.org/wiki/index.php/How_to_Obtain,_Build_and_Install_V4L-DVB_Device_Drivers
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.. [1] The upstream Linux Kernel development tree is located at
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https://git.kernel.org/pub/scm/li nux/kernel/git/torvalds/linux.git/
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Configuring the Linux Kernel
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============================
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You can access a menu of Kernel building options with::
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$ make menuconfig
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Then, select all desired options and exit it, saving the configuration.
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The changed configuration will be at the ``.config`` file. It would
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look like::
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...
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# CONFIG_RC_CORE is not set
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# CONFIG_CEC_CORE is not set
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CONFIG_MEDIA_SUPPORT=m
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CONFIG_MEDIA_SUPPORT_FILTER=y
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...
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The media subsystem is controlled by those menu configuration options::
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Device Drivers --->
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<M> Remote Controller support --->
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[ ] HDMI CEC RC integration
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[ ] Enable CEC error injection support
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[*] HDMI CEC drivers --->
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<*> Multimedia support --->
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The ``Remote Controller support`` option enables the core support for
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remote controllers\ [2]_.
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The ``HDMI CEC RC integration`` option enables integration of HDMI CEC
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with Linux, allowing to receive data via HDMI CEC as if it were produced
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by a remote controller directly connected to the machine.
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The ``HDMI CEC drivers`` option allow selecting platform and USB drivers
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that receives and/or transmits CEC codes via HDMI interfaces\ [3]_.
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The last option (``Multimedia support``) enables support for cameras,
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audio/video grabbers and TV.
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The media subsystem support can either be built together with the main
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Kernel or as a module. For most use cases, it is preferred to have it
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built as modules.
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.. note::
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Instead of using a menu, the Kernel provides a script with allows
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enabling configuration options directly. To enable media support
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and remote controller support using Kernel modules, you could use::
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$ scripts/config -m RC_CORE
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$ scripts/config -m MEDIA_SUPPORT
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.. [2] ``Remote Controller support`` should also be enabled if you
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want to use some TV card drivers that may depend on the remote
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controller core support.
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.. [3] Please notice that the DRM subsystem also have drivers for GPUs
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that use the media HDMI CEC support.
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Those GPU-specific drivers are selected via the ``Graphics support``
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menu, under ``Device Drivers``.
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When a GPU driver supports HDMI CEC, it will automatically
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enable the CEC core support at the media subsystem.
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Media dependencies
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------------------
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It should be noticed that enabling the above from a clean config is
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usually not enough. The media subsystem depends on several other Linux
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core support in order to work.
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For example, most media devices use a serial communication bus in
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order to talk with some peripherals. Such bus is called I²C
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(Inter-Integrated Circuit). In order to be able to build support
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for such hardware, the I²C bus support should be enabled, either via
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menu or with::
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./scripts/config -m I2C
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Another example: the remote controller core requires support for
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input devices, with can be enabled with::
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./scripts/config -m INPUT
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Other core functionality may also be needed (like PCI and/or USB support),
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depending on the specific driver(s) you would like to enable.
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Enabling Remote Controller Support
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----------------------------------
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The remote controller menu allows selecting drivers for specific devices.
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It's menu looks like this::
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--- Remote Controller support
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<M> Compile Remote Controller keymap modules
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[*] LIRC user interface
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[*] Support for eBPF programs attached to lirc devices
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[*] Remote controller decoders --->
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[*] Remote Controller devices --->
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The ``Compile Remote Controller keymap modules`` option creates key maps for
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several popular remote controllers.
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The ``LIRC user interface`` option adds enhanced functionality when using the
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``lirc`` program, by enabling an API that allows userspace to receive raw data
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from remote controllers.
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The ``Support for eBPF programs attached to lirc devices`` option allows
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the usage of special programs (called eBPF) that would allow aplications
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to add extra remote controller decoding functionality to the Linux Kernel.
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The ``Remote controller decoders`` option allows selecting the
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protocols that will be recognized by the Linux Kernel. Except if you
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want to disable some specific decoder, it is suggested to keep all
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sub-options enabled.
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The ``Remote Controller devices`` allows you to select the drivers
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that would be needed to support your device.
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The same configuration can also be set via the ``script/config``
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script. So, for instance, in order to support the ITE remote controller
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driver (found on Intel NUCs and on some ASUS x86 desktops), you could do::
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$ scripts/config -e INPUT
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$ scripts/config -e ACPI
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$ scripts/config -e MODULES
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$ scripts/config -m RC_CORE
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$ scripts/config -e RC_DEVICES
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$ scripts/config -e RC_DECODERS
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$ scripts/config -m IR_RC5_DECODER
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$ scripts/config -m IR_ITE_CIR
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Enabling HDMI CEC Support
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-------------------------
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The HDMI CEC support is set automatically when a driver requires it. So,
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all you need to do is to enable support either for a graphics card
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that needs it or by one of the existing HDMI drivers.
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The HDMI-specific drivers are available at the ``HDMI CEC drivers``
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menu\ [4]_::
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--- HDMI CEC drivers
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< > ChromeOS EC CEC driver
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< > Amlogic Meson AO CEC driver
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< > Amlogic Meson G12A AO CEC driver
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< > Generic GPIO-based CEC driver
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< > Samsung S5P CEC driver
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< > STMicroelectronics STiH4xx HDMI CEC driver
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< > STMicroelectronics STM32 HDMI CEC driver
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< > Tegra HDMI CEC driver
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< > SECO Boards HDMI CEC driver
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[ ] SECO Boards IR RC5 support
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< > Pulse Eight HDMI CEC
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< > RainShadow Tech HDMI CEC
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.. [4] The above contents is just an example. The actual options for
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HDMI devices depends on the system's architecture and may vary
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on new Kernels.
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Enabling Media Support
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----------------------
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The Media menu has a lot more options than the remote controller menu.
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Once selected, you should see the following options::
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--- Media support
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[ ] Filter media drivers
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[*] Autoselect ancillary drivers
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Media device types --->
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Media core support --->
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Video4Linux options --->
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Media controller options --->
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Digital TV options --->
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HDMI CEC options --->
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Media drivers --->
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Media ancillary drivers --->
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Except if you know exactly what you're doing, or if you want to build
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a driver for a SoC platform, it is strongly recommended to keep the
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``Autoselect ancillary drivers`` option turned on, as it will auto-select
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the needed I²C ancillary drivers.
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There are now two ways to select media device drivers, as described
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below.
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``Filter media drivers`` menu
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^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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This menu is meant to easy setup for PC and Laptop hardware. It works
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by letting the user to specify what kind of media drivers are desired,
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with those options::
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[ ] Cameras and video grabbers
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[ ] Analog TV
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[ ] Digital TV
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[ ] AM/FM radio receivers/transmitters
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[ ] Software defined radio
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[ ] Platform-specific devices
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[ ] Test drivers
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So, if you want to add support to a camera or video grabber only,
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select just the first option. Multiple options are allowed.
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Once the options on this menu are selected, the building system will
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auto-select the needed core drivers in order to support the selected
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functionality.
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.. note::
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Most TV cards are hybrid: they support both Analog TV and Digital TV.
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If you have an hybrid card, you may need to enable both ``Analog TV``
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and ``Digital TV`` at the menu.
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When using this option, the defaults for the media support core
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functionality are usually good enough to provide the basic functionality
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for the driver. Yet, you could manually enable some desired extra (optional)
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functionality using the settings under each of the following
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``Media support`` sub-menus::
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Media core support --->
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Video4Linux options --->
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Media controller options --->
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Digital TV options --->
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HDMI CEC options --->
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Once you select the desired filters, the drivers that matches the filtering
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criteria will be available at the ``Media support->Media drivers`` sub-menu.
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``Media Core Support`` menu without filtering
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^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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If you disable the ``Filter media drivers`` menu, all drivers available
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for your system whose dependencies are met should be shown at the
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``Media drivers`` menu.
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Please notice, however, that you should first ensure that the
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``Media Core Support`` menu has all the core functionality your drivers
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would need, as otherwise the corresponding device drivers won't be shown.
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Example
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-------
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In order to enable modular support for one of the boards listed on
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:doc:`this table <cx231xx-cardlist>`, with modular media core modules, the
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``.config`` file should contain those lines::
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CONFIG_MODULES=y
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CONFIG_USB=y
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CONFIG_I2C=y
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CONFIG_INPUT=y
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CONFIG_RC_CORE=m
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CONFIG_MEDIA_SUPPORT=m
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CONFIG_MEDIA_SUPPORT_FILTER=y
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CONFIG_MEDIA_ANALOG_TV_SUPPORT=y
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CONFIG_MEDIA_DIGITAL_TV_SUPPORT=y
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CONFIG_MEDIA_USB_SUPPORT=y
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CONFIG_VIDEO_CX231XX=y
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CONFIG_VIDEO_CX231XX_DVB=y
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Building and installing a new Kernel
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====================================
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Once the ``.config`` file has everything needed, all it takes to build
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is to run the ``make`` command::
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$ make
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And then install the new Kernel and its modules::
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$ sudo make modules_install
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$ sudo make install
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Building just the new media drivers and core
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============================================
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Running a new development Kernel from the development tree is usually risky,
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because it may have experimental changes that may have bugs. So, there are
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some ways to build just the new drivers, using alternative trees.
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There is the `Linux Kernel backports project
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<https://backports.wiki.kernel.org/index.php/Main_Page>`_, with contains
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newer drivers meant to be compiled against stable Kernels.
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The LinuxTV developers, with are responsible for maintaining the media
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subsystem also maintains a backport tree, with just the media drivers
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daily updated from the newest kernel. Such tree is available at:
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https://git.linuxtv.org/media_build.git/
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It should be noticed that, while it should be relatively safe to use the
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``media_build`` tree for testing purposes, there are not warranties that
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it would work (or even build) on a random Kernel. This tree is maintained
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using a "best-efforts" principle, as time permits us to fix issues there.
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If you notice anything wrong on it, feel free to submit patches at the
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Linux media subsystem's mailing list: media@vger.kernel.org. Please
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add ``[PATCH media-build]`` at the e-mail's subject if you submit a new
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patch for the media-build.
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Before using it, you should run::
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$ ./build
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.. note::
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1) you may need to run it twice if the ``media-build`` tree gets
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updated;
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2) you may need to do a ``make distclean`` if you had built it
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in the past for a different Kernel version than the one you're
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currently using;
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3) by default, it will use the same config options for media as
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the ones defined on the Kernel you're running.
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In order to select different drivers or different config options,
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use::
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$ make menuconfig
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Then, you can build and install the new drivers::
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$ make && sudo make install
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This will override the previous media drivers that your Kernel were
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using.
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