This commit introduces a different interface to submit transfers, using
DMA descriptors.
The structure of the DMA descriptor is as follows:
struct dma_desc {
u32 flags,
u32 id,
u64 dest_addr,
u64 src_addr,
u64 next_sg_addr,
u32 y_len,
u32 x_len,
u32 src_stride,
u32 dst_stride,
};
The 'flags' field currently offers two control bits:
- bit 0: if set, the transfer will complete after this last descriptor
is processed, and the DMA core will go back to idle state; if cleared,
the next DMA descriptor pointed to by 'next_sg_addr' will be loaded.
- bit 1: if set, an end-of-transfer interrupt will be raised after the
memory segment pointed to by this descriptor has been transferred.
The 'id' field corresponds to an identifier of the descriptor.
The 'dest_addr' and 'src_addr' contain the destination and source
addresses to use for the transfer, respectively.
The 'x_len' field contains the number of bytes to transfer,
minus one.
The 'y_len', 'src_stride' and 'dst_stride' fields are only useful for
2D transfers, and should be set to zero if 2D transfers are not
required.
To start a transfer, the address of the first DMA descriptor must be
written to register 0x47c and the HWDESC bit of CONTROL register must
be set. The Scatter-Gather transfer is queued similarly to the simple
transfers, by writing 1 in TRANSFER_SUBMIT.
The Scatter-Gather interface has a dedicated AXI-MM bus configured for
read transfers, with its own dedicated clock, which can be asynchronous.
The Scatter-Gather reset is generated by the reset manager to reset the
logic after completing any pending transactions on the bus.
When the Scatter-Gather is enabled during runtime, the legacy cyclic
functionality of the DMA is disabled.
Signed-off-by: Ionut Podgoreanu <ionut.podgoreanu@analog.com>
Ionut Podgoreanu