1*4882a593Smuzhiyun.. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later 2*4882a593Smuzhiyun.. c:namespace:: DTV.dmx 3*4882a593Smuzhiyun 4*4882a593Smuzhiyun.. _DMX_REQBUFS: 5*4882a593Smuzhiyun 6*4882a593Smuzhiyun***************** 7*4882a593Smuzhiyunioctl DMX_REQBUFS 8*4882a593Smuzhiyun***************** 9*4882a593Smuzhiyun 10*4882a593SmuzhiyunName 11*4882a593Smuzhiyun==== 12*4882a593Smuzhiyun 13*4882a593SmuzhiyunDMX_REQBUFS - Initiate Memory Mapping and/or DMA buffer I/O 14*4882a593Smuzhiyun 15*4882a593Smuzhiyun.. warning:: this API is still experimental 16*4882a593Smuzhiyun 17*4882a593SmuzhiyunSynopsis 18*4882a593Smuzhiyun======== 19*4882a593Smuzhiyun 20*4882a593Smuzhiyun.. c:macro:: DMX_REQBUFS 21*4882a593Smuzhiyun 22*4882a593Smuzhiyun``int ioctl(int fd, DMX_REQBUFS, struct dmx_requestbuffers *argp)`` 23*4882a593Smuzhiyun 24*4882a593SmuzhiyunArguments 25*4882a593Smuzhiyun========= 26*4882a593Smuzhiyun 27*4882a593Smuzhiyun``fd`` 28*4882a593Smuzhiyun File descriptor returned by :c:func:`open()`. 29*4882a593Smuzhiyun 30*4882a593Smuzhiyun``argp`` 31*4882a593Smuzhiyun Pointer to struct :c:type:`dmx_requestbuffers`. 32*4882a593Smuzhiyun 33*4882a593SmuzhiyunDescription 34*4882a593Smuzhiyun=========== 35*4882a593Smuzhiyun 36*4882a593SmuzhiyunThis ioctl is used to initiate a memory mapped or DMABUF based demux I/O. 37*4882a593Smuzhiyun 38*4882a593SmuzhiyunMemory mapped buffers are located in device memory and must be allocated 39*4882a593Smuzhiyunwith this ioctl before they can be mapped into the application's address 40*4882a593Smuzhiyunspace. User buffers are allocated by applications themselves, and this 41*4882a593Smuzhiyunioctl is merely used to switch the driver into user pointer I/O mode and 42*4882a593Smuzhiyunto setup some internal structures. Similarly, DMABUF buffers are 43*4882a593Smuzhiyunallocated by applications through a device driver, and this ioctl only 44*4882a593Smuzhiyunconfigures the driver into DMABUF I/O mode without performing any direct 45*4882a593Smuzhiyunallocation. 46*4882a593Smuzhiyun 47*4882a593SmuzhiyunTo allocate device buffers applications initialize all fields of the 48*4882a593Smuzhiyunstruct :c:type:`dmx_requestbuffers` structure. They set the ``count`` field 49*4882a593Smuzhiyunto the desired number of buffers, and ``size`` to the size of each 50*4882a593Smuzhiyunbuffer. 51*4882a593Smuzhiyun 52*4882a593SmuzhiyunWhen the ioctl is called with a pointer to this structure, the driver will 53*4882a593Smuzhiyunattempt to allocate the requested number of buffers and it stores the actual 54*4882a593Smuzhiyunnumber allocated in the ``count`` field. The ``count`` can be smaller than the number requested, even zero, when the driver runs out of free memory. A larger 55*4882a593Smuzhiyunnumber is also possible when the driver requires more buffers to 56*4882a593Smuzhiyunfunction correctly. The actual allocated buffer size can is returned 57*4882a593Smuzhiyunat ``size``, and can be smaller than what's requested. 58*4882a593Smuzhiyun 59*4882a593SmuzhiyunWhen this I/O method is not supported, the ioctl returns an ``EOPNOTSUPP`` 60*4882a593Smuzhiyunerror code. 61*4882a593Smuzhiyun 62*4882a593SmuzhiyunApplications can call :ref:`DMX_REQBUFS` again to change the number of 63*4882a593Smuzhiyunbuffers, however this cannot succeed when any buffers are still mapped. 64*4882a593SmuzhiyunA ``count`` value of zero frees all buffers, after aborting or finishing 65*4882a593Smuzhiyunany DMA in progress. 66*4882a593Smuzhiyun 67*4882a593SmuzhiyunReturn Value 68*4882a593Smuzhiyun============ 69*4882a593Smuzhiyun 70*4882a593SmuzhiyunOn success 0 is returned, on error -1 and the ``errno`` variable is set 71*4882a593Smuzhiyunappropriately. The generic error codes are described at the 72*4882a593Smuzhiyun:ref:`Generic Error Codes <gen-errors>` chapter. 73*4882a593Smuzhiyun 74*4882a593SmuzhiyunEOPNOTSUPP 75*4882a593Smuzhiyun The the requested I/O method is not supported. 76