From 57f0f512b273f60d52568b8c6b77e17f5636edc0 Mon Sep 17 00:00:00 2001 From: André Fabian Silva Delgado Date: Wed, 5 Aug 2015 17:04:01 -0300 Subject: Initial import --- Documentation/DocBook/media/v4l/vidioc-reqbufs.xml | 137 +++++++++++++++++++++ 1 file changed, 137 insertions(+) create mode 100644 Documentation/DocBook/media/v4l/vidioc-reqbufs.xml (limited to 'Documentation/DocBook/media/v4l/vidioc-reqbufs.xml') diff --git a/Documentation/DocBook/media/v4l/vidioc-reqbufs.xml b/Documentation/DocBook/media/v4l/vidioc-reqbufs.xml new file mode 100644 index 000000000..78a06a9a5 --- /dev/null +++ b/Documentation/DocBook/media/v4l/vidioc-reqbufs.xml @@ -0,0 +1,137 @@ + + + ioctl VIDIOC_REQBUFS + &manvol; + + + + VIDIOC_REQBUFS + Initiate Memory Mapping or User Pointer I/O + + + + + + int ioctl + int fd + int request + struct v4l2_requestbuffers *argp + + + + + + Arguments + + + + fd + + &fd; + + + + request + + VIDIOC_REQBUFS + + + + argp + + + + + + + + + Description + +This ioctl is used to initiate memory mapped, +user pointer or DMABUF based I/O. Memory mapped buffers are located in +device memory and must be allocated with this ioctl before they can be mapped +into the application's address space. User buffers are allocated by +applications themselves, and this ioctl is merely used to switch the driver +into user pointer I/O mode and to setup some internal structures. +Similarly, DMABUF buffers are allocated by applications through a device +driver, and this ioctl only configures the driver into DMABUF I/O mode without +performing any direct allocation. + + To allocate device buffers applications initialize all fields of the +v4l2_requestbuffers structure. They set the +type field to the respective stream or buffer type, +the count field to the desired number of buffers, +memory must be set to the requested I/O method and +the reserved array must be zeroed. When the ioctl is +called with a pointer to this structure the driver will attempt to allocate the +requested number of buffers and it stores the actual number allocated in the +count field. It can be smaller than the number +requested, even zero, when the driver runs out of free memory. A larger number +is also possible when the driver requires more buffers to function correctly. +For example video output requires at least two buffers, one displayed and one +filled by the application. + When the I/O method is not supported the ioctl +returns an &EINVAL;. + + Applications can call VIDIOC_REQBUFS +again to change the number of buffers, however this cannot succeed +when any buffers are still mapped. A count +value of zero frees all buffers, after aborting or finishing any DMA +in progress, an implicit &VIDIOC-STREAMOFF;. + + + struct <structname>v4l2_requestbuffers</structname> + + &cs-str; + + + __u32 + count + The number of buffers requested or granted. + + + __u32 + type + Type of the stream or buffers, this is the same +as the &v4l2-format; type field. See for valid values. + + + __u32 + memory + Applications set this field to +V4L2_MEMORY_MMAP, +V4L2_MEMORY_DMABUF or +V4L2_MEMORY_USERPTR. See . + + + __u32 + reserved[2] + A place holder for future extensions. This array should +be zeroed by applications. + + + +
+ + + + &return-value; + + + + EINVAL + + The buffer type (type field) or the +requested I/O method (memory) is not +supported. + + + + + -- cgit v1.2.3-54-g00ecf