• Alexandre TORGUE's avatar
    stmmac: add DMA support for GMAC 4.xx · 48863ce5
    Alexandre TORGUE authored
    DMA behavior is linked to descriptor management:
    
    -descriptor mechanism (Tx for example, but it is exactly the same for RX):
    -useful registers:
    -DMA_CH#_TxDesc_Ring_Len: length of transmit descriptor ring
    -DMA_CH#_TxDesc_List_Address: start address of the ring
    	-DMA_CH#_TxDesc_Tail_Pointer: address of the last
    					      descriptor to send + 1.
    	-DMA_CH#_TxDesc_Current_App_TxDesc: address of the current
    						    descriptor
    
    -The descriptor Tail Pointer register contains the pointer to the
     descriptor address (N). The base address and the current
     descriptor decide the address of the current descriptor that the
     DMA can process. The descriptors up to one location less than the
     one indicated by the descriptor tail pointer (N-1) are owned by
     the DMA. The DMA continues to process the descriptors until the
     following condition occurs:
     "current descriptor pointer == Descriptor Tail pointer"
    
    Then the DMA goes into suspend mode. The application must perform
    a write to descriptor tail pointer register and update the tail
    pointer to have the following condition and to start a new transfer:
    "current descriptor pointer < Descriptor tail pointer"
    
    The DMA automatically wraps around the base address when the end
    of ring is reached.
    
    Up to 8 DMA could be use but currently we only use one (channel0)
    Signed-off-by: default avatarAlexandre TORGUE <alexandre.torgue@st.com>
    Signed-off-by: default avatarGiuseppe Cavallaro <peppe.cavallaro@st.com>
    Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
    48863ce5
Makefile 923 Bytes