1.. -*- coding: utf-8; mode: rst -*- 2 3.. _VIDIOC_SUBDEV_G_FMT: 4 5********************************************** 6ioctl VIDIOC_SUBDEV_G_FMT, VIDIOC_SUBDEV_S_FMT 7********************************************** 8 9Name 10==== 11 12VIDIOC_SUBDEV_G_FMT - VIDIOC_SUBDEV_S_FMT - Get or set the data format on a subdev pad 13 14 15Synopsis 16======== 17 18.. c:function:: int ioctl( int fd, VIDIOC_SUBDEV_G_FMT, struct v4l2_subdev_format *argp ) 19 :name: VIDIOC_SUBDEV_G_FMT 20 21.. c:function:: int ioctl( int fd, VIDIOC_SUBDEV_S_FMT, struct v4l2_subdev_format *argp ) 22 :name: VIDIOC_SUBDEV_S_FMT 23 24 25Arguments 26========= 27 28``fd`` 29 File descriptor returned by :ref:`open() <func-open>`. 30 31``argp`` 32 Pointer to struct :c:type:`v4l2_subdev_format`. 33 34 35Description 36=========== 37 38These ioctls are used to negotiate the frame format at specific subdev 39pads in the image pipeline. 40 41To retrieve the current format applications set the ``pad`` field of a 42struct :c:type:`v4l2_subdev_format` to the desired 43pad number as reported by the media API and the ``which`` field to 44``V4L2_SUBDEV_FORMAT_ACTIVE``. When they call the 45``VIDIOC_SUBDEV_G_FMT`` ioctl with a pointer to this structure the 46driver fills the members of the ``format`` field. 47 48To change the current format applications set both the ``pad`` and 49``which`` fields and all members of the ``format`` field. When they call 50the ``VIDIOC_SUBDEV_S_FMT`` ioctl with a pointer to this structure the 51driver verifies the requested format, adjusts it based on the hardware 52capabilities and configures the device. Upon return the struct 53:c:type:`v4l2_subdev_format` contains the current 54format as would be returned by a ``VIDIOC_SUBDEV_G_FMT`` call. 55 56Applications can query the device capabilities by setting the ``which`` 57to ``V4L2_SUBDEV_FORMAT_TRY``. When set, 'try' formats are not applied 58to the device by the driver, but are changed exactly as active formats 59and stored in the sub-device file handle. Two applications querying the 60same sub-device would thus not interact with each other. 61 62For instance, to try a format at the output pad of a sub-device, 63applications would first set the try format at the sub-device input with 64the ``VIDIOC_SUBDEV_S_FMT`` ioctl. They would then either retrieve the 65default format at the output pad with the ``VIDIOC_SUBDEV_G_FMT`` ioctl, 66or set the desired output pad format with the ``VIDIOC_SUBDEV_S_FMT`` 67ioctl and check the returned value. 68 69Try formats do not depend on active formats, but can depend on the 70current links configuration or sub-device controls value. For instance, 71a low-pass noise filter might crop pixels at the frame boundaries, 72modifying its output frame size. 73 74Drivers must not return an error solely because the requested format 75doesn't match the device capabilities. They must instead modify the 76format to match what the hardware can provide. The modified format 77should be as close as possible to the original request. 78 79 80.. tabularcolumns:: |p{4.4cm}|p{4.4cm}|p{8.7cm}| 81 82.. c:type:: v4l2_subdev_format 83 84.. flat-table:: struct v4l2_subdev_format 85 :header-rows: 0 86 :stub-columns: 0 87 :widths: 1 1 2 88 89 * - __u32 90 - ``pad`` 91 - Pad number as reported by the media controller API. 92 * - __u32 93 - ``which`` 94 - Format to modified, from enum 95 :ref:`v4l2_subdev_format_whence <v4l2-subdev-format-whence>`. 96 * - struct :c:type:`v4l2_mbus_framefmt` 97 - ``format`` 98 - Definition of an image format, see :c:type:`v4l2_mbus_framefmt` for 99 details. 100 * - __u32 101 - ``reserved``\ [8] 102 - Reserved for future extensions. Applications and drivers must set 103 the array to zero. 104 105 106 107.. tabularcolumns:: |p{6.6cm}|p{2.2cm}|p{8.7cm}| 108 109.. _v4l2-subdev-format-whence: 110 111.. flat-table:: enum v4l2_subdev_format_whence 112 :header-rows: 0 113 :stub-columns: 0 114 :widths: 3 1 4 115 116 * - V4L2_SUBDEV_FORMAT_TRY 117 - 0 118 - Try formats, used for querying device capabilities. 119 * - V4L2_SUBDEV_FORMAT_ACTIVE 120 - 1 121 - Active formats, applied to the hardware. 122 123 124Return Value 125============ 126 127On success 0 is returned, on error -1 and the ``errno`` variable is set 128appropriately. The generic error codes are described at the 129:ref:`Generic Error Codes <gen-errors>` chapter. 130 131EBUSY 132 The format can't be changed because the pad is currently busy. This 133 can be caused, for instance, by an active video stream on the pad. 134 The ioctl must not be retried without performing another action to 135 fix the problem first. Only returned by ``VIDIOC_SUBDEV_S_FMT`` 136 137EINVAL 138 The struct :c:type:`v4l2_subdev_format` 139 ``pad`` references a non-existing pad, or the ``which`` field 140 references a non-existing format. 141 142 143============ 144 145On success 0 is returned, on error -1 and the ``errno`` variable is set 146appropriately. The generic error codes are described at the 147:ref:`Generic Error Codes <gen-errors>` chapter. 148