xiaoxiang781216 commented on pull request #4900:
URL: https://github.com/apache/incubator-nuttx/pull/4900#issuecomment-980066203


   > > Why not use some bounce buffer in SDMMC driver or switch to PIO mode to 
migrate the hardware limitation? You can't fix all location which access SD or 
EMMC card.
   > 
   > The FAT already has a mechanism for this. Performance and wasting 
resources.
   > 
   
   But, can you modify all file system(e.g. add SMARTFS_DMAMEMORY, 
SPIFFS_DMAMEMORY....) supported by NuttX? Even you modify all file system, user 
space application can still access block device directly. mkfatfs is one but 
not the last one.
   
   > How would you envision the bounce buffer implementation usage? Would it 
take more resources?
   
   At least one block buffer is required. It looks better to improve the bounce 
buffer to the block level cache which resolve DMA limitation in the universal 
way and improve the performance at the same time.


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