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stmmac: add descriptors function for GMAC 4.xx
One of main changes of GMAC 4.xx IP is descriptors management.
-descriptors are only used in ring mode.
-A descriptor is composed of 4 32bits registers (no more extended
descriptors)
-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.
-New features are available on IP:
-TSO (TCP Segmentation Offload) for TX only
-Split header: to have header and payload in 2 different buffers
Signed-off-by: Alexandre TORGUE <alexandre.torgue@st.com>
Signed-off-by: Giuseppe Cavallaro <peppe.cavallaro@st.com>
Signed-off-by: David S. Miller <davem@davemloft.net>