xref: /linux/Documentation/userspace-api/media/v4l/vidioc-querycap.rst (revision 55d0969c451159cff86949b38c39171cab962069) 
1.. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later
2.. c:namespace:: V4L
3
4.. _VIDIOC_QUERYCAP:
5
6*********************
7ioctl VIDIOC_QUERYCAP
8*********************
9
10Name
11====
12
13VIDIOC_QUERYCAP - Query device capabilities
14
15Synopsis
16========
17
18.. c:macro:: VIDIOC_QUERYCAP
19
20``int ioctl(int fd, VIDIOC_QUERYCAP, struct v4l2_capability *argp)``
21
22Arguments
23=========
24
25``fd``
26    File descriptor returned by :c:func:`open()`.
27
28``argp``
29    Pointer to struct :c:type:`v4l2_capability`.
30
31Description
32===========
33
34All V4L2 devices support the ``VIDIOC_QUERYCAP`` ioctl. It is used to
35identify kernel devices compatible with this specification and to obtain
36information about driver and hardware capabilities. The ioctl takes a
37pointer to a struct :c:type:`v4l2_capability` which is
38filled by the driver. When the driver is not compatible with this
39specification the ioctl returns an ``EINVAL`` error code.
40
41.. c:type:: v4l2_capability
42
43.. tabularcolumns:: |p{1.4cm}|p{2.8cm}|p{13.1cm}|
44
45.. cssclass:: longtable
46
47.. flat-table:: struct v4l2_capability
48    :header-rows:  0
49    :stub-columns: 0
50    :widths:       3 4 20
51
52    * - __u8
53      - ``driver``\ [16]
54      - Name of the driver, a unique NUL-terminated ASCII string. For
55	example: "bttv". Driver specific applications can use this
56	information to verify the driver identity. It is also useful to
57	work around known bugs, or to identify drivers in error reports.
58
59	Storing strings in fixed sized arrays is bad practice but
60	unavoidable here. Drivers and applications should take precautions
61	to never read or write beyond the end of the array and to make
62	sure the strings are properly NUL-terminated.
63    * - __u8
64      - ``card``\ [32]
65      - Name of the device, a NUL-terminated UTF-8 string. For example:
66	"Yoyodyne TV/FM". One driver may support different brands or
67	models of video hardware. This information is intended for users,
68	for example in a menu of available devices. Since multiple TV
69	cards of the same brand may be installed which are supported by
70	the same driver, this name should be combined with the character
71	device file name (e. g. ``/dev/video2``) or the ``bus_info``
72	string to avoid ambiguities.
73    * - __u8
74      - ``bus_info``\ [32]
75      - Location of the device in the system, a NUL-terminated ASCII
76	string. For example: "PCI:0000:05:06.0". This information is
77	intended for users, to distinguish multiple identical devices. If
78	no such information is available the field must simply count the
79	devices controlled by the driver ("platform:vivid-000"). The
80	bus_info must start with "PCI:" for PCI boards, "PCIe:" for PCI
81	Express boards, "usb-" for USB devices, "I2C:" for i2c devices,
82	"ISA:" for ISA devices, "parport" for parallel port devices and
83	"platform:" for platform devices.
84    * - __u32
85      - ``version``
86      - Version number of the driver.
87
88	Starting with kernel 3.1, the version reported is provided by the
89	V4L2 subsystem following the kernel numbering scheme. However, it
90	may not always return the same version as the kernel if, for
91	example, a stable or distribution-modified kernel uses the V4L2
92	stack from a newer kernel.
93
94	The version number is formatted using the ``KERNEL_VERSION()``
95	macro. For example if the media stack corresponds to the V4L2
96	version shipped with Kernel 4.14, it would be equivalent to:
97    * - :cspan:`2`
98
99	``#define KERNEL_VERSION(a,b,c) (((a) << 16) + ((b) << 8) + (c))``
100
101	``__u32 version = KERNEL_VERSION(4, 14, 0);``
102
103	``printf ("Version: %u.%u.%u\\n",``
104
105	``(version >> 16) & 0xFF, (version >> 8) & 0xFF, version & 0xFF);``
106    * - __u32
107      - ``capabilities``
108      - Available capabilities of the physical device as a whole, see
109	:ref:`device-capabilities`. The same physical device can export
110	multiple devices in /dev (e.g. /dev/videoX, /dev/vbiY and
111	/dev/radioZ). The ``capabilities`` field should contain a union of
112	all capabilities available around the several V4L2 devices
113	exported to userspace. For all those devices the ``capabilities``
114	field returns the same set of capabilities. This allows
115	applications to open just one of the devices (typically the video
116	device) and discover whether video, vbi and/or radio are also
117	supported.
118    * - __u32
119      - ``device_caps``
120      - Device capabilities of the opened device, see
121	:ref:`device-capabilities`. Should contain the available
122	capabilities of that specific device node. So, for example,
123	``device_caps`` of a radio device will only contain radio related
124	capabilities and no video or vbi capabilities. This field is only
125	set if the ``capabilities`` field contains the
126	``V4L2_CAP_DEVICE_CAPS`` capability. Only the ``capabilities``
127	field can have the ``V4L2_CAP_DEVICE_CAPS`` capability,
128	``device_caps`` will never set ``V4L2_CAP_DEVICE_CAPS``.
129    * - __u32
130      - ``reserved``\ [3]
131      - Reserved for future extensions. Drivers must set this array to
132	zero.
133
134
135.. tabularcolumns:: |p{7.0cm}|p{2.6cm}|p{7.7cm}|
136
137.. _device-capabilities:
138
139.. cssclass:: longtable
140
141.. flat-table:: Device Capabilities Flags
142    :header-rows:  0
143    :stub-columns: 0
144    :widths:       3 1 4
145
146    * - ``V4L2_CAP_VIDEO_CAPTURE``
147      - 0x00000001
148      - The device supports the single-planar API through the
149	:ref:`Video Capture <capture>` interface.
150    * - ``V4L2_CAP_VIDEO_CAPTURE_MPLANE``
151      - 0x00001000
152      - The device supports the :ref:`multi-planar API <planar-apis>`
153	through the :ref:`Video Capture <capture>` interface.
154    * - ``V4L2_CAP_VIDEO_OUTPUT``
155      - 0x00000002
156      - The device supports the single-planar API through the
157	:ref:`Video Output <output>` interface.
158    * - ``V4L2_CAP_VIDEO_OUTPUT_MPLANE``
159      - 0x00002000
160      - The device supports the :ref:`multi-planar API <planar-apis>`
161	through the :ref:`Video Output <output>` interface.
162    * - ``V4L2_CAP_VIDEO_M2M``
163      - 0x00008000
164      - The device supports the single-planar API through the Video
165	Memory-To-Memory interface.
166    * - ``V4L2_CAP_VIDEO_M2M_MPLANE``
167      - 0x00004000
168      - The device supports the :ref:`multi-planar API <planar-apis>`
169	through the Video Memory-To-Memory interface.
170    * - ``V4L2_CAP_VIDEO_OVERLAY``
171      - 0x00000004
172      - The device supports the :ref:`Video Overlay <overlay>`
173	interface. A video overlay device typically stores captured images
174	directly in the video memory of a graphics card, with hardware
175	clipping and scaling.
176    * - ``V4L2_CAP_VBI_CAPTURE``
177      - 0x00000010
178      - The device supports the :ref:`Raw VBI Capture <raw-vbi>`
179	interface, providing Teletext and Closed Caption data.
180    * - ``V4L2_CAP_VBI_OUTPUT``
181      - 0x00000020
182      - The device supports the :ref:`Raw VBI Output <raw-vbi>`
183	interface.
184    * - ``V4L2_CAP_SLICED_VBI_CAPTURE``
185      - 0x00000040
186      - The device supports the :ref:`Sliced VBI Capture <sliced>`
187	interface.
188    * - ``V4L2_CAP_SLICED_VBI_OUTPUT``
189      - 0x00000080
190      - The device supports the :ref:`Sliced VBI Output <sliced>`
191	interface.
192    * - ``V4L2_CAP_RDS_CAPTURE``
193      - 0x00000100
194      - The device supports the :ref:`RDS <rds>` capture interface.
195    * - ``V4L2_CAP_VIDEO_OUTPUT_OVERLAY``
196      - 0x00000200
197      - The device supports the :ref:`Video Output Overlay <osd>` (OSD)
198	interface. Unlike the *Video Overlay* interface, this is a
199	secondary function of video output devices and overlays an image
200	onto an outgoing video signal. When the driver sets this flag, it
201	must clear the ``V4L2_CAP_VIDEO_OVERLAY`` flag and vice
202	versa. [#f1]_
203    * - ``V4L2_CAP_HW_FREQ_SEEK``
204      - 0x00000400
205      - The device supports the
206	:ref:`VIDIOC_S_HW_FREQ_SEEK` ioctl
207	for hardware frequency seeking.
208    * - ``V4L2_CAP_RDS_OUTPUT``
209      - 0x00000800
210      - The device supports the :ref:`RDS <rds>` output interface.
211    * - ``V4L2_CAP_TUNER``
212      - 0x00010000
213      - The device has some sort of tuner to receive RF-modulated video
214	signals. For more information about tuner programming see
215	:ref:`tuner`.
216    * - ``V4L2_CAP_AUDIO``
217      - 0x00020000
218      - The device has audio inputs or outputs. It may or may not support
219	audio recording or playback, in PCM or compressed formats. PCM
220	audio support must be implemented as ALSA or OSS interface. For
221	more information on audio inputs and outputs see :ref:`audio`.
222    * - ``V4L2_CAP_RADIO``
223      - 0x00040000
224      - This is a radio receiver.
225    * - ``V4L2_CAP_MODULATOR``
226      - 0x00080000
227      - The device has some sort of modulator to emit RF-modulated
228	video/audio signals. For more information about modulator
229	programming see :ref:`tuner`.
230    * - ``V4L2_CAP_SDR_CAPTURE``
231      - 0x00100000
232      - The device supports the :ref:`SDR Capture <sdr>` interface.
233    * - ``V4L2_CAP_EXT_PIX_FORMAT``
234      - 0x00200000
235      - The device supports the struct
236	:c:type:`v4l2_pix_format` extended fields.
237    * - ``V4L2_CAP_SDR_OUTPUT``
238      - 0x00400000
239      - The device supports the :ref:`SDR Output <sdr>` interface.
240    * - ``V4L2_CAP_META_CAPTURE``
241      - 0x00800000
242      - The device supports the :ref:`metadata` capture interface.
243    * - ``V4L2_CAP_READWRITE``
244      - 0x01000000
245      - The device supports the :c:func:`read()` and/or
246	:c:func:`write()` I/O methods.
247    * - ``V4L2_CAP_EDID``
248      - 0x02000000
249      - The device stores the EDID for a video input, or retrieves the EDID for a video
250        output. It is a standalone EDID device, so no video streaming etc. will take place.
251
252        For a video input this is typically an eeprom that supports the
253        :ref:`VESA Enhanced Display Data Channel Standard <vesaeddc>`. It can be something
254        else as well, for example a micro controller.
255
256        For a video output this is typically read from an external device such as an
257        HDMI splitter accessed by a serial port.
258    * - ``V4L2_CAP_STREAMING``
259      - 0x04000000
260      - The device supports the :ref:`streaming <mmap>` I/O method.
261    * - ``V4L2_CAP_META_OUTPUT``
262      - 0x08000000
263      - The device supports the :ref:`metadata` output interface.
264    * - ``V4L2_CAP_TOUCH``
265      - 0x10000000
266      - This is a touch device.
267    * - ``V4L2_CAP_IO_MC``
268      - 0x20000000
269      - There is only one input and/or output seen from userspace. The whole
270        video topology configuration, including which I/O entity is routed to
271        the input/output, is configured by userspace via the Media Controller.
272        See :ref:`media_controller`.
273    * - ``V4L2_CAP_DEVICE_CAPS``
274      - 0x80000000
275      - The driver fills the ``device_caps`` field. This capability can
276	only appear in the ``capabilities`` field and never in the
277	``device_caps`` field.
278
279Return Value
280============
281
282On success 0 is returned, on error -1 and the ``errno`` variable is set
283appropriately. The generic error codes are described at the
284:ref:`Generic Error Codes <gen-errors>` chapter.
285
286.. [#f1]
287   The struct :c:type:`v4l2_framebuffer` lacks an
288   enum :c:type:`v4l2_buf_type` field, therefore the
289   type of overlay is implied by the driver capabilities.
290