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diff --git a/Documentation/admin-guide/media/building.rst b/Documentation/admin-guide/media/building.rst new file mode 100644 index 000000000..2d660b76c --- /dev/null +++ b/Documentation/admin-guide/media/building.rst @@ -0,0 +1,357 @@ +.. SPDX-License-Identifier: GPL-2.0 + +=================================== +Building support for a media device +=================================== + +The first step is to download the Kernel's source code, either via a +distribution-specific source file or via the Kernel's main git tree\ [1]_. + +Please notice, however, that, if: + +- you're a braveheart and want to experiment with new stuff; +- if you want to report a bug; +- if you're developing new patches + +you should use the main media development tree ``master`` branch: + + https://git.linuxtv.org/media_tree.git/ + +In this case, you may find some useful information at the +`LinuxTv wiki pages <https://linuxtv.org/wiki>`_: + + https://linuxtv.org/wiki/index.php/How_to_Obtain,_Build_and_Install_V4L-DVB_Device_Drivers + +.. [1] The upstream Linux Kernel development tree is located at + + https://git.kernel.org/pub/scm/li nux/kernel/git/torvalds/linux.git/ + +Configuring the Linux Kernel +============================ + +You can access a menu of Kernel building options with:: + + $ make menuconfig + +Then, select all desired options and exit it, saving the configuration. + +The changed configuration will be at the ``.config`` file. It would +look like:: + + ... + # CONFIG_RC_CORE is not set + # CONFIG_CEC_CORE is not set + CONFIG_MEDIA_SUPPORT=m + CONFIG_MEDIA_SUPPORT_FILTER=y + ... + +The media subsystem is controlled by those menu configuration options:: + + Device Drivers ---> + <M> Remote Controller support ---> + [ ] HDMI CEC RC integration + [ ] Enable CEC error injection support + [*] HDMI CEC drivers ---> + <*> Multimedia support ---> + +The ``Remote Controller support`` option enables the core support for +remote controllers\ [2]_. + +The ``HDMI CEC RC integration`` option enables integration of HDMI CEC +with Linux, allowing to receive data via HDMI CEC as if it were produced +by a remote controller directly connected to the machine. + +The ``HDMI CEC drivers`` option allow selecting platform and USB drivers +that receives and/or transmits CEC codes via HDMI interfaces\ [3]_. + +The last option (``Multimedia support``) enables support for cameras, +audio/video grabbers and TV. + +The media subsystem support can either be built together with the main +Kernel or as a module. For most use cases, it is preferred to have it +built as modules. + +.. note:: + + Instead of using a menu, the Kernel provides a script with allows + enabling configuration options directly. To enable media support + and remote controller support using Kernel modules, you could use:: + + $ scripts/config -m RC_CORE + $ scripts/config -m MEDIA_SUPPORT + +.. [2] ``Remote Controller support`` should also be enabled if you + want to use some TV card drivers that may depend on the remote + controller core support. + +.. [3] Please notice that the DRM subsystem also have drivers for GPUs + that use the media HDMI CEC support. + + Those GPU-specific drivers are selected via the ``Graphics support`` + menu, under ``Device Drivers``. + + When a GPU driver supports HDMI CEC, it will automatically + enable the CEC core support at the media subsystem. + +Media dependencies +------------------ + +It should be noticed that enabling the above from a clean config is +usually not enough. The media subsystem depends on several other Linux +core support in order to work. + +For example, most media devices use a serial communication bus in +order to talk with some peripherals. Such bus is called I²C +(Inter-Integrated Circuit). In order to be able to build support +for such hardware, the I²C bus support should be enabled, either via +menu or with:: + + ./scripts/config -m I2C + +Another example: the remote controller core requires support for +input devices, with can be enabled with:: + + ./scripts/config -m INPUT + +Other core functionality may also be needed (like PCI and/or USB support), +depending on the specific driver(s) you would like to enable. + +Enabling Remote Controller Support +---------------------------------- + +The remote controller menu allows selecting drivers for specific devices. +It's menu looks like this:: + + --- Remote Controller support + <M> Compile Remote Controller keymap modules + [*] LIRC user interface + [*] Support for eBPF programs attached to lirc devices + [*] Remote controller decoders ---> + [*] Remote Controller devices ---> + +The ``Compile Remote Controller keymap modules`` option creates key maps for +several popular remote controllers. + +The ``LIRC user interface`` option adds enhanced functionality when using the +``lirc`` program, by enabling an API that allows userspace to receive raw data +from remote controllers. + +The ``Support for eBPF programs attached to lirc devices`` option allows +the usage of special programs (called eBPF) that would allow aplications +to add extra remote controller decoding functionality to the Linux Kernel. + +The ``Remote controller decoders`` option allows selecting the +protocols that will be recognized by the Linux Kernel. Except if you +want to disable some specific decoder, it is suggested to keep all +sub-options enabled. + +The ``Remote Controller devices`` allows you to select the drivers +that would be needed to support your device. + +The same configuration can also be set via the ``script/config`` +script. So, for instance, in order to support the ITE remote controller +driver (found on Intel NUCs and on some ASUS x86 desktops), you could do:: + + $ scripts/config -e INPUT + $ scripts/config -e ACPI + $ scripts/config -e MODULES + $ scripts/config -m RC_CORE + $ scripts/config -e RC_DEVICES + $ scripts/config -e RC_DECODERS + $ scripts/config -m IR_RC5_DECODER + $ scripts/config -m IR_ITE_CIR + +Enabling HDMI CEC Support +------------------------- + +The HDMI CEC support is set automatically when a driver requires it. So, +all you need to do is to enable support either for a graphics card +that needs it or by one of the existing HDMI drivers. + +The HDMI-specific drivers are available at the ``HDMI CEC drivers`` +menu\ [4]_:: + + --- HDMI CEC drivers + < > ChromeOS EC CEC driver + < > Amlogic Meson AO CEC driver + < > Amlogic Meson G12A AO CEC driver + < > Generic GPIO-based CEC driver + < > Samsung S5P CEC driver + < > STMicroelectronics STiH4xx HDMI CEC driver + < > STMicroelectronics STM32 HDMI CEC driver + < > Tegra HDMI CEC driver + < > SECO Boards HDMI CEC driver + [ ] SECO Boards IR RC5 support + < > Pulse Eight HDMI CEC + < > RainShadow Tech HDMI CEC + +.. [4] The above contents is just an example. The actual options for + HDMI devices depends on the system's architecture and may vary + on new Kernels. + +Enabling Media Support +---------------------- + +The Media menu has a lot more options than the remote controller menu. +Once selected, you should see the following options:: + + --- Media support + [ ] Filter media drivers + [*] Autoselect ancillary drivers + Media device types ---> + Media core support ---> + Video4Linux options ---> + Media controller options ---> + Digital TV options ---> + HDMI CEC options ---> + Media drivers ---> + Media ancillary drivers ---> + +Except if you know exactly what you're doing, or if you want to build +a driver for a SoC platform, it is strongly recommended to keep the +``Autoselect ancillary drivers`` option turned on, as it will auto-select +the needed I²C ancillary drivers. + +There are now two ways to select media device drivers, as described +below. + +``Filter media drivers`` menu +^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ + +This menu is meant to easy setup for PC and Laptop hardware. It works +by letting the user to specify what kind of media drivers are desired, +with those options:: + + [ ] Cameras and video grabbers + [ ] Analog TV + [ ] Digital TV + [ ] AM/FM radio receivers/transmitters + [ ] Software defined radio + [ ] Platform-specific devices + [ ] Test drivers + +So, if you want to add support to a camera or video grabber only, +select just the first option. Multiple options are allowed. + +Once the options on this menu are selected, the building system will +auto-select the needed core drivers in order to support the selected +functionality. + +.. note:: + + Most TV cards are hybrid: they support both Analog TV and Digital TV. + + If you have an hybrid card, you may need to enable both ``Analog TV`` + and ``Digital TV`` at the menu. + +When using this option, the defaults for the media support core +functionality are usually good enough to provide the basic functionality +for the driver. Yet, you could manually enable some desired extra (optional) +functionality using the settings under each of the following +``Media support`` sub-menus:: + + Media core support ---> + Video4Linux options ---> + Media controller options ---> + Digital TV options ---> + HDMI CEC options ---> + +Once you select the desired filters, the drivers that matches the filtering +criteria will be available at the ``Media support->Media drivers`` sub-menu. + +``Media Core Support`` menu without filtering +^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ + +If you disable the ``Filter media drivers`` menu, all drivers available +for your system whose dependencies are met should be shown at the +``Media drivers`` menu. + +Please notice, however, that you should first ensure that the +``Media Core Support`` menu has all the core functionality your drivers +would need, as otherwise the corresponding device drivers won't be shown. + +Example +------- + +In order to enable modular support for one of the boards listed on +:doc:`this table <cx231xx-cardlist>`, with modular media core modules, the +``.config`` file should contain those lines:: + + CONFIG_MODULES=y + CONFIG_USB=y + CONFIG_I2C=y + CONFIG_INPUT=y + CONFIG_RC_CORE=m + CONFIG_MEDIA_SUPPORT=m + CONFIG_MEDIA_SUPPORT_FILTER=y + CONFIG_MEDIA_ANALOG_TV_SUPPORT=y + CONFIG_MEDIA_DIGITAL_TV_SUPPORT=y + CONFIG_MEDIA_USB_SUPPORT=y + CONFIG_VIDEO_CX231XX=y + CONFIG_VIDEO_CX231XX_DVB=y + +Building and installing a new Kernel +==================================== + +Once the ``.config`` file has everything needed, all it takes to build +is to run the ``make`` command:: + + $ make + +And then install the new Kernel and its modules:: + + $ sudo make modules_install + $ sudo make install + +Building just the new media drivers and core +============================================ + +Running a new development Kernel from the development tree is usually risky, +because it may have experimental changes that may have bugs. So, there are +some ways to build just the new drivers, using alternative trees. + +There is the `Linux Kernel backports project +<https://backports.wiki.kernel.org/index.php/Main_Page>`_, with contains +newer drivers meant to be compiled against stable Kernels. + +The LinuxTV developers, with are responsible for maintaining the media +subsystem also maintains a backport tree, with just the media drivers +daily updated from the newest kernel. Such tree is available at: + +https://git.linuxtv.org/media_build.git/ + +It should be noticed that, while it should be relatively safe to use the +``media_build`` tree for testing purposes, there are not warranties that +it would work (or even build) on a random Kernel. This tree is maintained +using a "best-efforts" principle, as time permits us to fix issues there. + +If you notice anything wrong on it, feel free to submit patches at the +Linux media subsystem's mailing list: media@vger.kernel.org. Please +add ``[PATCH media-build]`` at the e-mail's subject if you submit a new +patch for the media-build. + +Before using it, you should run:: + + $ ./build + +.. note:: + + 1) you may need to run it twice if the ``media-build`` tree gets + updated; + 2) you may need to do a ``make distclean`` if you had built it + in the past for a different Kernel version than the one you're + currently using; + 3) by default, it will use the same config options for media as + the ones defined on the Kernel you're running. + +In order to select different drivers or different config options, +use:: + + $ make menuconfig + +Then, you can build and install the new drivers:: + + $ make && sudo make install + +This will override the previous media drivers that your Kernel were +using. |