According to your comments, devxdmah2c0 is a character device, and thus it is not possible to use mmap on it - that just makes no sense, primarily because it's not an addressable device (you can't use lseek() fseek() either). If the FPGA's address space is presented via PCI PCIe, then you might have luck with using lspci to locate its memory regions, opening devmem, and using.
I have developed a pcie v4l2 driver support V4L2MEMORYMMAP feature,and can capture video from pcie (FPGA). I have disable pcie MMU and reserved specific address used by pcie in dts file. Base on tegremultimediaapi sample 12camerav4l2cuda, I used memcopy API copy camera data to nvbuffer then did format convert and render. Thats work fine.
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CPM4, which contains two controllers for PCI Express, also integrates one instance of a QDMA XDMA and bridge subsystem from the Xilinx IP portfolio. Use of the integrated DMA is optional, and when used, can be configured as a QDMA subsystem like that in the CPM5, or as an XDMA subsystem. Data can be moved with memory-mapped techniques.
A. Tradeoffs between mmap IO and le IO system calls Basically, le IO via mmap() is considered as a advanced le IO because mmap() IO has lots of advantages such as fewer number of memory copies. In addition to these mer-its, mmap() has several advantages making memory-mapped le IO to be more sophisticated than read()write.