[GitHub] [incubator-nuttx-apps] patacongo edited a comment on pull request #338: fsutils/mkfatfs: use DMA memory for mkfatfs when needed

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patacongo edited a comment on pull request #338:
URL: https://github.com/apache/incubator-nuttx-apps/pull/338#issuecomment-662477210


   Linux has exactly the same issues.  But people have developed Linux device drivers for allocating user-space DMA buffers.  For example https://github.com/ikwzm/udmabuf
   
   Something like that would be a POSIX compatible solution that should not get too much resistance.
   
   Also related:
   https://xilinx-wiki.atlassian.net/wiki/spaces/A/pages/18842418/Linux+DMA+From+User+Space
   https://stackoverflow.com/questions/5539375/linux-kernel-device-driver-to-dma-from-a-device-into-user-space-memory
   
   I haven't thought through all of the details, but I suspect the the mmap() function could be exteneded to allocate user-space DMA-able memory, at least under certain circumstances.  The current NuttX mmap() function is, however, really on a stub and none of the more exotic mmap() functionality is implemented.  I think it would have to use a scatter-gather DMA interface to be usable since mmap() does not guarantee physically contiguous allocations.
   
   Any solution would be a LOT of work to fix something that is not broken.


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