use of malloc(9) for DMA buffers

["Marco Trillo" <marcotrillo%gmail.com@localhost>]

Hi,

I have a doubt regarding dbdma.c dbdma_alloc(). It uses malloc(9) to
allocate the buffer for the DMA command descriptors:

  122: dbdma_command_t        *
  123: dbdma_alloc(size)
  124:        int size;
  125: {
  126:        u_int buf;
  127:
  128:        buf = (u_int)malloc(size + 0x0f, M_DEVBUF, M_WAITOK);
  129:        buf = (buf + 0x0f) & ~0x0f;
  130:
  131:        return (dbdma_command_t *)buf;
  132: }

Since these descriptors are directly accessed by hardware, wouldn't
this cause problems if the buffer crosses a page boundary and so it's
not contiguous in physical memory? Or does this never happen?


Thanks,
Marco.