UM0851 datasheet(167/245 Pages) STMICROELECTRONICS

167 / 245 page

UM0851

Accelerator engine device drivers

Doc ID 16604 Rev 2

167/245

DWC_CTL_USER_MODE | DWC_CTL_NON_BUFFERABLE | DWC_CTL_NON_CACHEABLE |

DWC_CTL_DEST_BURST(BURST_8) | DWC_CTL_SRC_BURST(BURST_8) |

DWC_CTL_DEST_WIDTH(width) | DWC_CTL_SRC_WIDTH(width) | DWC_CTL_DEST_ADDR_INC |

DWC_CTL_SRC_ADDR_INC

The default DMA driver cfg configuration for memset and memory-to-memory transfers is:

DWC_CFG_FLOW_CTRL(DMA_MEMORY_TO_MEMORY)

DMA transfer preparation

Before requesting a DMA transfer, you should increment the usage count of channel per

CPU using the following function call.

static inline void dma_chan_get(struct dma_chan *chan);

This is important for multiprocessor systems. This function keeps note of the channel used

per CPU.

There are three different types of transfers:

Memory to memory

Memory to memory or memcpy transfers can be prepared using two different routines.

The first routine is exported from the DMA framework. It first synchronizes source memory

between RAM and cache, then prepares the transfer and finally starts the transfer. On

completion of DMA transfer it does not call any client driver callback. It can work with either

the default configuration of the DMA driver or a configuration provided by the client (if the

slave pointer in the client structure is non NULL).

chan: is a pointer to DMA channel allocated to client.

dest and src: are destination and source memory addresses.

len: number of bytes to be copied.

dma_cookie_t: non negative value of cookie indicates success in preparing and

starting transfer. On error cookie is negative. */

dma_cookie_t dma_async_memcpy_buf_to_buf(struct dma_chan *chan, void *dest, void

*src, size_t len);

For transfer completion notification refer to Transfer completion notification section.

The second routine is exported from the DMA driver. In this routine, synchronization issues

are expected to be handled by the client driver. Firstly you need to prepare transfers, then

assign any callback if required and then start the actual transfer.

A transfer is prepared by the following call.

/* flags: if you don't want the DMA driver to call dma_unmap_single, for src and dest

addresses, after completion of transfer then you can pass DMA_COMPL_SKIP_SRC_UNMAP

or DMA_COMPL_SKIP_DEST_UNMAP in flags parameter (for both bitwise OR is used).

dma_async_tx_descriptor: It is the descriptor which contains the prepared transfer

information. If must be non NULL for successful prepration of DMA transfer. */

struct dma_async_tx_descriptor * device_prep_dma_memcpy(struct dma_chan *chan,

dma_addr_t dest, dma_addr_t src, size_t len, unsigned long flags);

/* It can't be called directly, call it using chan pointer */

tx = chan->device->device_prep_dma_memcpy(chan, dest, src, len, flags);

Check the Start transfer section below for for details on starting the actual transfer.

UM0851 Datasheet(PDF) 167 Page - STMicroelectronics

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