yf13 commented on PR #12041:
URL: https://github.com/apache/nuttx/pull/12041#issuecomment-2035884137

   @pussuw thanks for the explanations.
   
   did you mean that we only
   - reuse the `vm_alloc_region()` and `vm_alloc_release()` for virtual address 
allocation.
   - reuse the `up_shmat()` and `up_shmdt()` for mapping/unmapping.
   and don't use anything in "mm/shm"?
   
   The memory mapping zone is defined by `ARCH_SHM_NPAGES` and 
`ARCH_SHM_MAXREGIONS` etc, as long as the virtual zone is big enough to hold 
both shared memory and device mapping requirements, we don't need worry about 
affecting the shared memory use cases as the device memory mappings don't 
occupy any shmid. Is this correct?
   
   As `vm_alloc_region()` has limitations and can't do 640x480x4=1228800 frame 
buffer yet, maybe we can use static virtual address plan for devices now? If 
so, should the static address space be separated from the dynamic space?
   


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