Hi,

one case that I forgot to mention:

On Sun, 28 Aug 2011, Paul Walmsley wrote:

Several upstream device drivers get their DMA request line IDs from the 
device data format[14][15][16].  But more drivers should be doing this 
than currently are[17]:

- the device driver author may have hardcoded the DMA request line ID, 
  assuming it would never change

- DMA could be broken on the device due to hardware bugs, so it is unused

- the driver author may just never have gotten around to implementing DMA, 
  or was reassigned to another project, or couldn't figure it out

- the device may have its own internal DMA controller logic, so support 
  for an external DMA controller was simply never added

- the driver may be using software-initiated DMA, which doesn't use a 
  DMA request line, nor does it rely on the device to start or stop DMA.
  Instead, the CPU reprograms the DMA controller when the driver receives 
  an interrupt


- Paul