[GitHub] [incubator-nuttx] hartmannathan commented on pull request #4900: Add Board IOCTL for DMA buffer allocation

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hartmannathan commented on pull request #4900:
URL: https://github.com/apache/incubator-nuttx/pull/4900#issuecomment-981103849


   This seems more like an architecture issue than a board issue. It will affect all boards using STM32F7, H7, F4. Also problems related to memory regions and DMA will keep coming back again and again unless there is a universal solution. See for example PR #3198: https://github.com/apache/incubator-nuttx/pull/3198 where I ran into issues because SPI6 can only DMA to/from RAM4.
   
   I think memory allocation restrictions only apply to DMA, regardless of architecture. Some architectures can DMA all DMA-aware peripherals to all their memory (e.g., TM4C12x), others can't.
   
   So I think what we need is a special OS-level memory allocator specifically for allocating DMA buffers. It would take some kind of flags indicating which peripheral(s) and direction(s) (memory-to-peripheral, peripheral-to-memory, both), and in turn it would call an arch-specific allocator that knows all the constraints for that arch and therefore can allocate memory in the correct region and alignment.
   
   Then this can be hooked up to a boardctl or ioctl, allowing applications to allocate memory that fits the constraints.
   
   Thoughts?


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