From 5b7c4cabbb65f5c469464da6c5f614cbd7f730f2 Mon Sep 17 00:00:00 2001 From: Linus Torvalds Date: Tue, 21 Feb 2023 18:24:12 -0800 Subject: Merge tag 'net-next-6.3' of git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net-next Pull networking updates from Jakub Kicinski: "Core: - Add dedicated kmem_cache for typical/small skb->head, avoid having to access struct page at kfree time, and improve memory use. - Introduce sysctl to set default RPS configuration for new netdevs. - Define Netlink protocol specification format which can be used to describe messages used by each family and auto-generate parsers. Add tools for generating kernel data structures and uAPI headers. - Expose all net/core sysctls inside netns. - Remove 4s sleep in netpoll if carrier is instantly detected on boot. - Add configurable limit of MDB entries per port, and port-vlan. - Continue populating drop reasons throughout the stack. - Retire a handful of legacy Qdiscs and classifiers. Protocols: - Support IPv4 big TCP (TSO frames larger than 64kB). - Add IP_LOCAL_PORT_RANGE socket option, to control local port range on socket by socket basis. - Track and report in procfs number of MPTCP sockets used. - Support mixing IPv4 and IPv6 flows in the in-kernel MPTCP path manager. - IPv6: don't check net.ipv6.route.max_size and rely on garbage collection to free memory (similarly to IPv4). - Support Penultimate Segment Pop (PSP) flavor in SRv6 (RFC8986). - ICMP: add per-rate limit counters. - Add support for user scanning requests in ieee802154. - Remove static WEP support. - Support minimal Wi-Fi 7 Extremely High Throughput (EHT) rate reporting. - WiFi 7 EHT channel puncturing support (client & AP). BPF: - Add a rbtree data structure following the "next-gen data structure" precedent set by recently added linked list, that is, by using kfunc + kptr instead of adding a new BPF map type. - Expose XDP hints via kfuncs with initial support for RX hash and timestamp metadata. - Add BPF_F_NO_TUNNEL_KEY extension to bpf_skb_set_tunnel_key to better support decap on GRE tunnel devices not operating in collect metadata. - Improve x86 JIT's codegen for PROBE_MEM runtime error checks. - Remove the need for trace_printk_lock for bpf_trace_printk and bpf_trace_vprintk helpers. - Extend libbpf's bpf_tracing.h support for tracing arguments of kprobes/uprobes and syscall as a special case. - Significantly reduce the search time for module symbols by livepatch and BPF. - Enable cpumasks to be used as kptrs, which is useful for tracing programs tracking which tasks end up running on which CPUs in different time intervals. - Add support for BPF trampoline on s390x and riscv64. - Add capability to export the XDP features supported by the NIC. - Add __bpf_kfunc tag for marking kernel functions as kfuncs. - Add cgroup.memory=nobpf kernel parameter option to disable BPF memory accounting for container environments. Netfilter: - Remove the CLUSTERIP target. It has been marked as obsolete for years, and we still have WARN splats wrt races of the out-of-band /proc interface installed by this target. - Add 'destroy' commands to nf_tables. They are identical to the existing 'delete' commands, but do not return an error if the referenced object (set, chain, rule...) did not exist. Driver API: - Improve cpumask_local_spread() locality to help NICs set the right IRQ affinity on AMD platforms. - Separate C22 and C45 MDIO bus transactions more clearly. - Introduce new DCB table to control DSCP rewrite on egress. - Support configuration of Physical Layer Collision Avoidance (PLCA) Reconciliation Sublayer (RS) (802.3cg-2019). Modern version of shared medium Ethernet. - Support for MAC Merge layer (IEEE 802.3-2018 clause 99). Allowing preemption of low priority frames by high priority frames. - Add support for controlling MACSec offload using netlink SET. - Rework devlink instance refcounts to allow registration and de-registration under the instance lock. Split the code into multiple files, drop some of the unnecessarily granular locks and factor out common parts of netlink operation handling. - Add TX frame aggregation parameters (for USB drivers). - Add a new attr TCA_EXT_WARN_MSG to report TC (offload) warning messages with notifications for debug. - Allow offloading of UDP NEW connections via act_ct. - Add support for per action HW stats in TC. - Support hardware miss to TC action (continue processing in SW from a specific point in the action chain). - Warn if old Wireless Extension user space interface is used with modern cfg80211/mac80211 drivers. Do not support Wireless Extensions for Wi-Fi 7 devices at all. Everyone should switch to using nl80211 interface instead. - Improve the CAN bit timing configuration. Use extack to return error messages directly to user space, update the SJW handling, including the definition of a new default value that will benefit CAN-FD controllers, by increasing their oscillator tolerance. New hardware / drivers: - Ethernet: - nVidia BlueField-3 support (control traffic driver) - Ethernet support for imx93 SoCs - Motorcomm yt8531 gigabit Ethernet PHY - onsemi NCN26000 10BASE-T1S PHY (with support for PLCA) - Microchip LAN8841 PHY (incl. cable diagnostics and PTP) - Amlogic gxl MDIO mux - WiFi: - RealTek RTL8188EU (rtl8xxxu) - Qualcomm Wi-Fi 7 devices (ath12k) - CAN: - Renesas R-Car V4H Drivers: - Bluetooth: - Set Per Platform Antenna Gain (PPAG) for Intel controllers. - Ethernet NICs: - Intel (1G, igc): - support TSN / Qbv / packet scheduling features of i226 model - Intel (100G, ice): - use GNSS subsystem instead of TTY - multi-buffer XDP support - extend support for GPIO pins to E823 devices - nVidia/Mellanox: - update the shared buffer configuration on PFC commands - implement PTP adjphase function for HW offset control - TC support for Geneve and GRE with VF tunnel offload - more efficient crypto key management method - multi-port eswitch support - Netronome/Corigine: - add DCB IEEE support - support IPsec offloading for NFP3800 - Freescale/NXP (enetc): - support XDP_REDIRECT for XDP non-linear buffers - improve reconfig, avoid link flap and waiting for idle - support MAC Merge layer - Other NICs: - sfc/ef100: add basic devlink support for ef100 - ionic: rx_push mode operation (writing descriptors via MMIO) - bnxt: use the auxiliary bus abstraction for RDMA - r8169: disable ASPM and reset bus in case of tx timeout - cpsw: support QSGMII mode for J721e CPSW9G - cpts: support pulse-per-second output - ngbe: add an mdio bus driver - usbnet: optimize usbnet_bh() by avoiding unnecessary queuing - r8152: handle devices with FW with NCM support - amd-xgbe: support 10Mbps, 2.5GbE speeds and rx-adaptation - virtio-net: support multi buffer XDP - virtio/vsock: replace virtio_vsock_pkt with sk_buff - tsnep: XDP support - Ethernet high-speed switches: - nVidia/Mellanox (mlxsw): - add support for latency TLV (in FW control messages) - Microchip (sparx5): - separate explicit and implicit traffic forwarding rules, make the implicit rules always active - add support for egress DSCP rewrite - IS0 VCAP support (Ingress Classification) - IS2 VCAP filters (protos, L3 addrs, L4 ports, flags, ToS etc.) - ES2 VCAP support (Egress Access Control) - support for Per-Stream Filtering and Policing (802.1Q, 8.6.5.1) - Ethernet embedded switches: - Marvell (mv88e6xxx): - add MAB (port auth) offload support - enable PTP receive for mv88e6390 - NXP (ocelot): - support MAC Merge layer - support for the the vsc7512 internal copper phys - Microchip: - lan9303: convert to PHYLINK - lan966x: support TC flower filter statistics - lan937x: PTP support for KSZ9563/KSZ8563 and LAN937x - lan937x: support Credit Based Shaper configuration - ksz9477: support Energy Efficient Ethernet - other: - qca8k: convert to regmap read/write API, use bulk operations - rswitch: Improve TX timestamp accuracy - Intel WiFi (iwlwifi): - EHT (Wi-Fi 7) rate reporting - STEP equalizer support: transfer some STEP (connection to radio on platforms with integrated wifi) related parameters from the BIOS to the firmware. - Qualcomm 802.11ax WiFi (ath11k): - IPQ5018 support - Fine Timing Measurement (FTM) responder role support - channel 177 support - MediaTek WiFi (mt76): - per-PHY LED support - mt7996: EHT (Wi-Fi 7) support - Wireless Ethernet Dispatch (WED) reset support - switch to using page pool allocator - RealTek WiFi (rtw89): - support new version of Bluetooth co-existance - Mobile: - rmnet: support TX aggregation" * tag 'net-next-6.3' of git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net-next: (1872 commits) page_pool: add a comment explaining the fragment counter usage net: ethtool: fix __ethtool_dev_mm_supported() implementation ethtool: pse-pd: Fix double word in comments xsk: add linux/vmalloc.h to xsk.c sefltests: netdevsim: wait for devlink instance after netns removal selftest: fib_tests: Always cleanup before exit net/mlx5e: Align IPsec ASO result memory to be as required by hardware net/mlx5e: TC, Set CT miss to the specific ct action instance net/mlx5e: Rename CHAIN_TO_REG to MAPPED_OBJ_TO_REG net/mlx5: Refactor tc miss handling to a single function net/mlx5: Kconfig: Make tc offload depend on tc skb extension net/sched: flower: Support hardware miss to tc action net/sched: flower: Move filter handle initialization earlier net/sched: cls_api: Support hardware miss to tc action net/sched: Rename user cookie and act cookie sfc: fix builds without CONFIG_RTC_LIB sfc: clean up some inconsistent indentings net/mlx4_en: Introduce flexible array to silence overflow warning net: lan966x: Fix possible deadlock inside PTP net/ulp: Remove redundant ->clone() test in inet_clone_ulp(). ... --- Documentation/userspace-api/media/v4l/open.rst | 238 +++++++++++++++++++++++++ 1 file changed, 238 insertions(+) create mode 100644 Documentation/userspace-api/media/v4l/open.rst (limited to 'Documentation/userspace-api/media/v4l/open.rst') diff --git a/Documentation/userspace-api/media/v4l/open.rst b/Documentation/userspace-api/media/v4l/open.rst new file mode 100644 index 000000000..18bfb9b81 --- /dev/null +++ b/Documentation/userspace-api/media/v4l/open.rst @@ -0,0 +1,238 @@ +.. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later +.. c:namespace:: V4L + +.. _open: + +*************************** +Opening and Closing Devices +*************************** + +.. _v4l2_hardware_control: + +Controlling a hardware peripheral via V4L2 +========================================== + +Hardware that is supported using the V4L2 uAPI often consists of multiple +devices or peripherals, each of which have their own driver. + +The bridge driver exposes one or more V4L2 device nodes +(see :ref:`v4l2_device_naming`). + +There are other drivers providing support for other components of +the hardware, which may also expose device nodes, called V4L2 sub-devices. + +When such V4L2 sub-devices are exposed, they allow controlling those +other hardware components - usually connected via a serial bus (like +I²C, SMBus or SPI). Depending on the bridge driver, those sub-devices +can be controlled indirectly via the bridge driver or explicitly via +the :ref:`Media Controller ` and via the +:ref:`V4L2 sub-devices `. + +The devices that require the use of the +:ref:`Media Controller ` are called **MC-centric** +devices. The devices that are fully controlled via V4L2 device nodes +are called **video-node-centric**. + +Userspace can check if a V4L2 hardware peripheral is MC-centric by +calling :ref:`VIDIOC_QUERYCAP` and checking the +:ref:`device_caps field `. + +If the device returns ``V4L2_CAP_IO_MC`` flag at ``device_caps``, +then it is MC-centric, otherwise, it is video-node-centric. + +It is required for MC-centric drivers to identify the V4L2 +sub-devices and to configure the pipelines via the +:ref:`media controller API ` before using the peripheral. +Also, the sub-devices' configuration shall be controlled via the +:ref:`sub-device API `. + +.. note:: + + A video-node-centric may still provide media-controller and + sub-device interfaces as well. + + However, in that case the media-controller and the sub-device + interfaces are read-only and just provide information about the + device. The actual configuration is done via the video nodes. + +.. _v4l2_device_naming: + +V4L2 Device Node Naming +======================= + +V4L2 drivers are implemented as kernel modules, loaded manually by the +system administrator or automatically when a device is first discovered. +The driver modules plug into the ``videodev`` kernel module. It provides +helper functions and a common application interface specified in this +document. + +Each driver thus loaded registers one or more device nodes with major +number 81. Minor numbers are allocated dynamically unless the kernel +is compiled with the kernel option CONFIG_VIDEO_FIXED_MINOR_RANGES. +In that case minor numbers are allocated in ranges depending on the +device node type. + +The device nodes supported by the Video4Linux subsystem are: + +======================== ==================================================== +Default device node name Usage +======================== ==================================================== +``/dev/videoX`` Video and metadata for capture/output devices +``/dev/vbiX`` Vertical blank data (i.e. closed captions, teletext) +``/dev/radioX`` Radio tuners and modulators +``/dev/swradioX`` Software Defined Radio tuners and modulators +``/dev/v4l-touchX`` Touch sensors +``/dev/v4l-subdevX`` Video sub-devices (used by sensors and other + components of the hardware peripheral)\ [#]_ +======================== ==================================================== + +Where ``X`` is a non-negative integer. + +.. note:: + + 1. The actual device node name is system-dependent, as udev rules may apply. + 2. There is no guarantee that ``X`` will remain the same for the same + device, as the number depends on the device driver's probe order. + If you need an unique name, udev default rules produce + ``/dev/v4l/by-id/`` and ``/dev/v4l/by-path/`` directories containing + links that can be used uniquely to identify a V4L2 device node:: + + $ tree /dev/v4l + /dev/v4l + ├── by-id + │   └── usb-OmniVision._USB_Camera-B4.04.27.1-video-index0 -> ../../video0 + └── by-path + └── pci-0000:00:14.0-usb-0:2:1.0-video-index0 -> ../../video0 + +.. [#] **V4L2 sub-device nodes** (e. g. ``/dev/v4l-subdevX``) use a different + set of system calls, as covered at :ref:`subdev`. + +Many drivers support "video_nr", "radio_nr" or "vbi_nr" module +options to select specific video/radio/vbi node numbers. This allows the +user to request that the device node is named e.g. /dev/video5 instead +of leaving it to chance. When the driver supports multiple devices of +the same type more than one device node number can be assigned, +separated by commas: + +.. code-block:: none + + # modprobe mydriver video_nr=0,1 radio_nr=0,1 + +In ``/etc/modules.conf`` this may be written as: + +:: + + options mydriver video_nr=0,1 radio_nr=0,1 + +When no device node number is given as module option the driver supplies +a default. + +Normally udev will create the device nodes in /dev automatically for +you. If udev is not installed, then you need to enable the +CONFIG_VIDEO_FIXED_MINOR_RANGES kernel option in order to be able to +correctly relate a minor number to a device node number. I.e., you need +to be certain that minor number 5 maps to device node name video5. With +this kernel option different device types have different minor number +ranges. These ranges are listed in :ref:`devices`. + +The creation of character special files (with mknod) is a privileged +operation and devices cannot be opened by major and minor number. That +means applications cannot *reliably* scan for loaded or installed +drivers. The user must enter a device name, or the application can try +the conventional device names. + +.. _related: + +Related Devices +=============== + +Devices can support several functions. For example video capturing, VBI +capturing and radio support. + +The V4L2 API creates different V4L2 device nodes for each of these functions. + +The V4L2 API was designed with the idea that one device node could +support all functions. However, in practice this never worked: this +'feature' was never used by applications and many drivers did not +support it and if they did it was certainly never tested. In addition, +switching a device node between different functions only works when +using the streaming I/O API, not with the +:c:func:`read()`/\ :c:func:`write()` API. + +Today each V4L2 device node supports just one function. + +Besides video input or output the hardware may also support audio +sampling or playback. If so, these functions are implemented as ALSA PCM +devices with optional ALSA audio mixer devices. + +One problem with all these devices is that the V4L2 API makes no +provisions to find these related V4L2 device nodes. Some really complex +hardware use the Media Controller (see :ref:`media_controller`) which can +be used for this purpose. But several drivers do not use it, and while some +code exists that uses sysfs to discover related V4L2 device nodes (see +libmedia_dev in the +`v4l-utils `__ git +repository), there is no library yet that can provide a single API +towards both Media Controller-based devices and devices that do not use +the Media Controller. If you want to work on this please write to the +linux-media mailing list: +`https://linuxtv.org/lists.php `__. + +Multiple Opens +============== + +V4L2 devices can be opened more than once. [#f1]_ When this is supported +by the driver, users can for example start a "panel" application to +change controls like brightness or audio volume, while another +application captures video and audio. In other words, panel applications +are comparable to an ALSA audio mixer application. Just opening a V4L2 +device should not change the state of the device. [#f2]_ + +Once an application has allocated the memory buffers needed for +streaming data (by calling the :ref:`VIDIOC_REQBUFS` +or :ref:`VIDIOC_CREATE_BUFS` ioctls, or +implicitly by calling the :c:func:`read()` or +:c:func:`write()` functions) that application (filehandle) +becomes the owner of the device. It is no longer allowed to make changes +that would affect the buffer sizes (e.g. by calling the +:ref:`VIDIOC_S_FMT ` ioctl) and other applications are +no longer allowed to allocate buffers or start or stop streaming. The +EBUSY error code will be returned instead. + +Merely opening a V4L2 device does not grant exclusive access. [#f3]_ +Initiating data exchange however assigns the right to read or write the +requested type of data, and to change related properties, to this file +descriptor. Applications can request additional access privileges using +the priority mechanism described in :ref:`app-pri`. + +Shared Data Streams +=================== + +V4L2 drivers should not support multiple applications reading or writing +the same data stream on a device by copying buffers, time multiplexing +or similar means. This is better handled by a proxy application in user +space. + +Functions +========= + +To open and close V4L2 devices applications use the +:c:func:`open()` and :c:func:`close()` function, +respectively. Devices are programmed using the +:ref:`ioctl() ` function as explained in the following +sections. + +.. [#f1] + There are still some old and obscure drivers that have not been + updated to allow for multiple opens. This implies that for such + drivers :c:func:`open()` can return an ``EBUSY`` error code + when the device is already in use. + +.. [#f2] + Unfortunately, opening a radio device often switches the state of the + device to radio mode in many drivers. This behavior should be fixed + eventually as it violates the V4L2 specification. + +.. [#f3] + Drivers could recognize the ``O_EXCL`` open flag. Presently this is + not required, so applications cannot know if it really works. -- cgit v1.2.3