--- zzzz-none-000/linux-3.10.107/Documentation/DocBook/media/v4l/common.xml 2017-06-27 09:49:32.000000000 +0000 +++ scorpion-7490-727/linux-3.10.107/Documentation/DocBook/media/v4l/common.xml 2021-02-04 17:41:59.000000000 +0000 @@ -38,70 +38,41 @@ V4L2 drivers are implemented as kernel modules, loaded manually by the system administrator or automatically when a device is -first opened. The driver modules plug into the "videodev" kernel +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 and a minor number between 0 and 255. Assigning -minor numbers to V4L2 devices is entirely up to the system administrator, -this is primarily intended to solve conflicts between devices. - Access permissions are associated with character -device special files, hence we must ensure device numbers cannot -change with the module load order. To this end minor numbers are no -longer automatically assigned by the "videodev" module as in V4L but -requested by the driver. The defaults will suffice for most people -unless two drivers compete for the same minor numbers. - The module options to select minor numbers are named -after the device special file with a "_nr" suffix. For example "video_nr" -for /dev/video video capture devices. The number is -an offset to the base minor number associated with the device type. - - In earlier versions of the V4L2 API the module options -where named after the device special file with a "unit_" prefix, expressing -the minor number itself, not an offset. Rationale for this change is unknown. -Lastly the naming and semantics are just a convention among driver writers, -the point to note is that minor numbers are not supposed to be hardcoded -into drivers. - When the driver supports multiple devices of the same -type more than one minor number can be assigned, separated by commas: - +with major number 81 and a minor number between 0 and 255. 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 (video, radio, etc.). + + 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: + -> insmod mydriver.o video_nr=0,1 radio_nr=0,1 +> modprobe mydriver video_nr=0,1 radio_nr=0,1 In /etc/modules.conf this may be written as: -alias char-major-81-0 mydriver -alias char-major-81-1 mydriver -alias char-major-81-64 mydriver -options mydriver video_nr=0,1 radio_nr=0,1 +options mydriver video_nr=0,1 radio_nr=0,1 - - - When an application attempts to open a device -special file with major number 81 and minor number 0, 1, or 64, load -"mydriver" (and the "videodev" module it depends upon). - - - Register the first two video capture devices with -minor number 0 and 1 (base number is 0), the first two radio device -with minor number 64 and 65 (base 64). - - - When no minor number is given as module -option the driver supplies a default. -recommends the base minor numbers to be used for the various device -types. Obviously minor numbers must be unique. When the number is -already in use the offending device will not be -registered. - - By convention system administrators create various -character device special files with these major and minor numbers in -the /dev directory. The names recommended for the -different V4L2 device types are listed in . + 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 . The creation of character special files (with @@ -110,85 +81,66 @@ applications cannot reliable scan for loaded or installed drivers. The user must enter a device name, or the application can try the conventional device names. - - Under the device filesystem (devfs) the minor number -options are ignored. V4L2 drivers (or by proxy the "videodev" module) -automatically create the required device files in the -/dev/v4l directory using the conventional device -names above.
Multiple Opens - In general, V4L2 devices can be opened more than once. + V4L2 devices can be opened more than once. +There are still some old and obscure drivers that have not been updated to +allow for multiple opens. This implies that for such drivers &func-open; can +return an &EBUSY; when the device is already in use. 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 OSS or ALSA audio mixer application. -When a device supports multiple functions like capturing and overlay -simultaneously, multiple opens allow concurrent -use of the device by forked processes or specialized applications. - - Multiple opens are optional, although drivers should -permit at least concurrent accesses without data exchange, &ie; panel -applications. This implies &func-open; can return an &EBUSY; when the -device is already in use, as well as &func-ioctl; functions initiating -data exchange (namely the &VIDIOC-S-FMT; ioctl), and the &func-read; -and &func-write; functions. +applications are comparable to an ALSA audio mixer application. +Just opening a V4L2 device should not change the state of the device. +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. + + Once an application has allocated the memory buffers needed for +streaming data (by calling the &VIDIOC-REQBUFS; or &VIDIOC-CREATE-BUFS; ioctls, +or implicitly by calling the &func-read; or &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 &VIDIOC-S-FMT; ioctl) and other applications are no longer allowed to allocate +buffers or start or stop streaming. The &EBUSY; will be returned instead. - Mere opening a V4L2 device does not grant exclusive + Merely opening a V4L2 device does not grant exclusive access. Drivers could recognize the O_EXCL open flag. Presently this is not required, @@ -206,12 +158,7 @@ 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. When the driver supports stream -sharing anyway it must be implemented transparently. The V4L2 API does -not specify how conflicts are solved. +a proxy application in user space.
@@ -240,15 +187,15 @@ Starting with kernel version 3.1, VIDIOC-QUERYCAP will return the V4L2 API version used by the driver, with generally matches the Kernel version. -There's no need of using &VIDIOC-QUERYCAP; to check if an specific ioctl is -supported, the V4L2 core now returns ENOIOCTLCMD if a driver doesn't provide +There's no need of using &VIDIOC-QUERYCAP; to check if a specific ioctl is +supported, the V4L2 core now returns ENOTTY if a driver doesn't provide support for an ioctl. Other features can be queried by calling the respective ioctl, for example &VIDIOC-ENUMINPUT; to learn about the number, types and names of video connectors on the device. Although abstraction is a major objective of this API, the -ioctl also allows driver specific applications to reliable identify +&VIDIOC-QUERYCAP; ioctl also allows driver specific applications to reliably identify the driver. All V4L2 drivers must support @@ -278,9 +225,7 @@ the &VIDIOC-QUERYCAP; ioctl. Ioctls changing driver properties, such as &VIDIOC-S-INPUT;, -return an &EBUSY; after another application obtained higher priority. -An event mechanism to notify applications about asynchronous property -changes has been proposed but not added yet. +return an &EBUSY; after another application obtained higher priority.
@@ -288,9 +233,9 @@ Video inputs and outputs are physical connectors of a device. These can be for example RF connectors (antenna/cable), CVBS -a.k.a. Composite Video, S-Video or RGB connectors. Only video and VBI -capture devices have inputs, output devices have outputs, at least one -each. Radio devices have no video inputs or outputs. +a.k.a. Composite Video, S-Video or RGB connectors. Video and VBI +capture devices have inputs. Video and VBI output devices have outputs, +at least one each. Radio devices have no video inputs or outputs. To learn about the number and attributes of the available inputs and outputs applications can enumerate them with the @@ -299,30 +244,13 @@ ioctl also contains signal status information applicable when the current video input is queried. - The &VIDIOC-G-INPUT; and &VIDIOC-G-OUTPUT; ioctl return the + The &VIDIOC-G-INPUT; and &VIDIOC-G-OUTPUT; ioctls return the index of the current video input or output. To select a different input or output applications call the &VIDIOC-S-INPUT; and -&VIDIOC-S-OUTPUT; ioctl. Drivers must implement all the input ioctls +&VIDIOC-S-OUTPUT; ioctls. Drivers must implement all the input ioctls when the device has one or more inputs, all the output ioctls when the device has one or more outputs. - - Information about the current video input @@ -330,20 +258,20 @@ &v4l2-input; input; int index; -if (-1 == ioctl (fd, &VIDIOC-G-INPUT;, &index)) { - perror ("VIDIOC_G_INPUT"); - exit (EXIT_FAILURE); +if (-1 == ioctl(fd, &VIDIOC-G-INPUT;, &index)) { + perror("VIDIOC_G_INPUT"); + exit(EXIT_FAILURE); } -memset (&input, 0, sizeof (input)); +memset(&input, 0, sizeof(input)); input.index = index; -if (-1 == ioctl (fd, &VIDIOC-ENUMINPUT;, &input)) { - perror ("VIDIOC_ENUMINPUT"); - exit (EXIT_FAILURE); +if (-1 == ioctl(fd, &VIDIOC-ENUMINPUT;, &input)) { + perror("VIDIOC_ENUMINPUT"); + exit(EXIT_FAILURE); } -printf ("Current input: %s\n", input.name); +printf("Current input: %s\n", input.name); @@ -355,9 +283,9 @@ index = 0; -if (-1 == ioctl (fd, &VIDIOC-S-INPUT;, &index)) { - perror ("VIDIOC_S_INPUT"); - exit (EXIT_FAILURE); +if (-1 == ioctl(fd, &VIDIOC-S-INPUT;, &index)) { + perror("VIDIOC_S_INPUT"); + exit(EXIT_FAILURE); } @@ -397,7 +325,7 @@ also contains signal status information applicable when the current audio input is queried. - The &VIDIOC-G-AUDIO; and &VIDIOC-G-AUDOUT; ioctl report + The &VIDIOC-G-AUDIO; and &VIDIOC-G-AUDOUT; ioctls report the current audio input and output, respectively. Note that, unlike &VIDIOC-G-INPUT; and &VIDIOC-G-OUTPUT; these ioctls return a structure as VIDIOC_ENUMAUDIO and @@ -408,11 +336,11 @@ output (which presently has no changeable properties) applications call the &VIDIOC-S-AUDOUT; ioctl. - Drivers must implement all input ioctls when the device -has one or more inputs, all output ioctls when the device has one -or more outputs. When the device has any audio inputs or outputs the -driver must set the V4L2_CAP_AUDIO flag in the -&v4l2-capability; returned by the &VIDIOC-QUERYCAP; ioctl. + Drivers must implement all audio input ioctls when the device +has multiple selectable audio inputs, all audio output ioctls when the +device has multiple selectable audio outputs. When the device has any +audio inputs or outputs the driver must set the V4L2_CAP_AUDIO +flag in the &v4l2-capability; returned by the &VIDIOC-QUERYCAP; ioctl. Information about the current audio input @@ -420,14 +348,14 @@ &v4l2-audio; audio; -memset (&audio, 0, sizeof (audio)); +memset(&audio, 0, sizeof(audio)); -if (-1 == ioctl (fd, &VIDIOC-G-AUDIO;, &audio)) { - perror ("VIDIOC_G_AUDIO"); - exit (EXIT_FAILURE); +if (-1 == ioctl(fd, &VIDIOC-G-AUDIO;, &audio)) { + perror("VIDIOC_G_AUDIO"); + exit(EXIT_FAILURE); } -printf ("Current input: %s\n", audio.name); +printf("Current input: %s\n", audio.name); @@ -437,13 +365,13 @@ &v4l2-audio; audio; -memset (&audio, 0, sizeof (audio)); /* clear audio.mode, audio.reserved */ +memset(&audio, 0, sizeof(audio)); /* clear audio.mode, audio.reserved */ audio.index = 0; -if (-1 == ioctl (fd, &VIDIOC-S-AUDIO;, &audio)) { - perror ("VIDIOC_S_AUDIO"); - exit (EXIT_FAILURE); +if (-1 == ioctl(fd, &VIDIOC-S-AUDIO;, &audio)) { + perror("VIDIOC_S_AUDIO"); + exit(EXIT_FAILURE); } @@ -468,7 +396,7 @@ video inputs. To query and change tuner properties applications use the -&VIDIOC-G-TUNER; and &VIDIOC-S-TUNER; ioctl, respectively. The +&VIDIOC-G-TUNER; and &VIDIOC-S-TUNER; ioctls, respectively. The &v4l2-tuner; returned by VIDIOC_G_TUNER also contains signal status information applicable when the tuner of the current video or radio input is queried. Note that @@ -533,7 +461,7 @@ support another set of standards. This set is reported by the std field of &v4l2-input; and &v4l2-output; returned by the &VIDIOC-ENUMINPUT; and -&VIDIOC-ENUMOUTPUT; ioctl, respectively. +&VIDIOC-ENUMOUTPUT; ioctls, respectively. V4L2 defines one bit for each analog video standard currently in use worldwide, and sets aside bits for driver defined @@ -564,28 +492,10 @@ To query and select the standard used by the current video input or output applications call the &VIDIOC-G-STD; and &VIDIOC-S-STD; ioctl, respectively. The received -standard can be sensed with the &VIDIOC-QUERYSTD; ioctl. Note that the parameter of all these ioctls is a pointer to a &v4l2-std-id; type (a standard set), not an index into the standard enumeration. - An alternative to the current scheme is to use pointers -to indices as arguments of VIDIOC_G_STD and -VIDIOC_S_STD, the &v4l2-input; and -&v4l2-output; std field would be a set of -indices like audioset. - Indices are consistent with the rest of the API -and identify the standard unambiguously. In the present scheme of -things an enumerated standard is looked up by &v4l2-std-id;. Now the -standards supported by the inputs of a device can overlap. Just -assume the tuner and composite input in the example above both -exist on a device. An enumeration of "PAL-B/G", "PAL-H/I" suggests -a choice which does not exist. We cannot merge or omit sets, because -applications would be unable to find the standards reported by -VIDIOC_G_STD. That leaves separate enumerations -for each input. Also selecting a standard by &v4l2-std-id; can be -ambiguous. Advantage of this method is that applications need not -identify the standard indirectly, after enumerating.So in -summary, the lookup itself is unavoidable. The difference is only -whether the lookup is necessary to find an enumerated standard or to -switch to a standard by &v4l2-std-id;. - Drivers must implement all video standard ioctls +standard can be sensed with the &VIDIOC-QUERYSTD; ioctl. Note that the +parameter of all these ioctls is a pointer to a &v4l2-std-id; type +(a standard set), not an index into the standard +enumeration. Drivers must implement all video standard ioctls when the device has one or more video inputs or outputs. Special rules apply to devices such as USB cameras where the notion of video @@ -604,17 +514,10 @@ VIDIOC_S_STD, VIDIOC_QUERYSTD and VIDIOC_ENUMSTD ioctls shall return the -&ENOTTY;. - See for a rationale. +&ENOTTY; or the &EINVAL;. Applications can make use of the and flags to determine whether the video standard ioctls -are available for the device. - - See for a rationale. Probably -even USB cameras follow some well known video standard. It might have -been better to explicitly indicate elsewhere if a device cannot live -up to normal expectations, instead of this exception. - +can be used with the given input or output. Information about the current video standard @@ -623,22 +526,22 @@ &v4l2-std-id; std_id; &v4l2-standard; standard; -if (-1 == ioctl (fd, &VIDIOC-G-STD;, &std_id)) { +if (-1 == ioctl(fd, &VIDIOC-G-STD;, &std_id)) { /* Note when VIDIOC_ENUMSTD always returns ENOTTY this is no video device or it falls under the USB exception, and VIDIOC_G_STD returning ENOTTY is no error. */ - perror ("VIDIOC_G_STD"); - exit (EXIT_FAILURE); + perror("VIDIOC_G_STD"); + exit(EXIT_FAILURE); } -memset (&standard, 0, sizeof (standard)); +memset(&standard, 0, sizeof(standard)); standard.index = 0; -while (0 == ioctl (fd, &VIDIOC-ENUMSTD;, &standard)) { +while (0 == ioctl(fd, &VIDIOC-ENUMSTD;, &standard)) { if (standard.id & std_id) { - printf ("Current video standard: %s\n", standard.name); - exit (EXIT_SUCCESS); + printf("Current video standard: %s\n", standard.name); + exit(EXIT_SUCCESS); } standard.index++; @@ -648,8 +551,8 @@ empty unless this device falls under the USB exception. */ if (errno == EINVAL || standard.index == 0) { - perror ("VIDIOC_ENUMSTD"); - exit (EXIT_FAILURE); + perror("VIDIOC_ENUMSTD"); + exit(EXIT_FAILURE); } @@ -662,26 +565,26 @@ &v4l2-input; input; &v4l2-standard; standard; -memset (&input, 0, sizeof (input)); +memset(&input, 0, sizeof(input)); -if (-1 == ioctl (fd, &VIDIOC-G-INPUT;, &input.index)) { - perror ("VIDIOC_G_INPUT"); - exit (EXIT_FAILURE); +if (-1 == ioctl(fd, &VIDIOC-G-INPUT;, &input.index)) { + perror("VIDIOC_G_INPUT"); + exit(EXIT_FAILURE); } -if (-1 == ioctl (fd, &VIDIOC-ENUMINPUT;, &input)) { - perror ("VIDIOC_ENUM_INPUT"); - exit (EXIT_FAILURE); +if (-1 == ioctl(fd, &VIDIOC-ENUMINPUT;, &input)) { + perror("VIDIOC_ENUM_INPUT"); + exit(EXIT_FAILURE); } -printf ("Current input %s supports:\n", input.name); +printf("Current input %s supports:\n", input.name); -memset (&standard, 0, sizeof (standard)); +memset(&standard, 0, sizeof(standard)); standard.index = 0; -while (0 == ioctl (fd, &VIDIOC-ENUMSTD;, &standard)) { +while (0 == ioctl(fd, &VIDIOC-ENUMSTD;, &standard)) { if (standard.id & input.std) - printf ("%s\n", standard.name); + printf("%s\n", standard.name); standard.index++; } @@ -690,8 +593,8 @@ empty unless this device falls under the USB exception. */ if (errno != EINVAL || standard.index == 0) { - perror ("VIDIOC_ENUMSTD"); - exit (EXIT_FAILURE); + perror("VIDIOC_ENUMSTD"); + exit(EXIT_FAILURE); } @@ -703,21 +606,21 @@ &v4l2-input; input; &v4l2-std-id; std_id; -memset (&input, 0, sizeof (input)); +memset(&input, 0, sizeof(input)); -if (-1 == ioctl (fd, &VIDIOC-G-INPUT;, &input.index)) { - perror ("VIDIOC_G_INPUT"); - exit (EXIT_FAILURE); +if (-1 == ioctl(fd, &VIDIOC-G-INPUT;, &input.index)) { + perror("VIDIOC_G_INPUT"); + exit(EXIT_FAILURE); } -if (-1 == ioctl (fd, &VIDIOC-ENUMINPUT;, &input)) { - perror ("VIDIOC_ENUM_INPUT"); - exit (EXIT_FAILURE); +if (-1 == ioctl(fd, &VIDIOC-ENUMINPUT;, &input)) { + perror("VIDIOC_ENUM_INPUT"); + exit(EXIT_FAILURE); } if (0 == (input.std & V4L2_STD_PAL_BG)) { - fprintf (stderr, "Oops. B/G PAL is not supported.\n"); - exit (EXIT_FAILURE); + fprintf(stderr, "Oops. B/G PAL is not supported.\n"); + exit(EXIT_FAILURE); } /* Note this is also supposed to work when only B @@ -725,9 +628,9 @@ std_id = V4L2_STD_PAL_BG; -if (-1 == ioctl (fd, &VIDIOC-S-STD;, &std_id)) { - perror ("VIDIOC_S_STD"); - exit (EXIT_FAILURE); +if (-1 == ioctl(fd, &VIDIOC-S-STD;, &std_id)) { + perror("VIDIOC_S_STD"); + exit(EXIT_FAILURE); } @@ -740,26 +643,25 @@ such as High Definition TV interfaces (HDMI), VGA, DVI connectors etc., that carry video signals and there is a need to extend the API to select the video timings for these interfaces. Since it is not possible to extend the &v4l2-std-id; due to -the limited bits available, a new set of IOCTLs was added to set/get video timings at -the input and output: - - DV Timings: This will allow applications to define detailed -video timings for the interface. This includes parameters such as width, height, -polarities, frontporch, backporch etc. The linux/v4l2-dv-timings.h +the limited bits available, a new set of ioctls was added to set/get video timings at +the input and output. + + These ioctls deal with the detailed digital video timings that define +each video format. This includes parameters such as the active video width and height, +signal polarities, frontporches, backporches, sync widths etc. The linux/v4l2-dv-timings.h header can be used to get the timings of the formats in the and standards. - - - To enumerate and query the attributes of the DV timings supported by a device, + + To enumerate and query the attributes of the DV timings supported by a device applications use the &VIDIOC-ENUM-DV-TIMINGS; and &VIDIOC-DV-TIMINGS-CAP; ioctls. - To set DV timings for the device, applications use the + To set DV timings for the device applications use the &VIDIOC-S-DV-TIMINGS; ioctl and to get current DV timings they use the &VIDIOC-G-DV-TIMINGS; ioctl. To detect the DV timings as seen by the video receiver applications use the &VIDIOC-QUERY-DV-TIMINGS; ioctl. Applications can make use of the and - flags to decide what ioctls are available to set the -video timings for the device. + flags to determine whether the digital video ioctls +can be used with the given input or output.
&sub-controls;