UM0851 datasheet(168/245 Pages) STMICROELECTRONICS

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Accelerator engine device drivers

UM0851

168/245

Doc ID 16604 Rev 2

Memory set

Memory set is a important feature that is required a number of times. The 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. The routine 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).

A transfer is prepared by the following call.

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

dest: is destination memory address.

value: is value to be set at dest.

len: number of bytes to be copied.

flags: if you don't want the DMA driver to call dma_unmap_single, for dest address,

after completion of memset then you can pass 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 * spear_prep_dma_memset(struct dma_chan *chan,

dma_addr_t dest, int value, size_t len, unsigned long flags);

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

tx = chan->device->spear_prep_dma_memset(chan, dest, val, len, flags);

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

Peripheral to peripheral or memory to/from peripheral transfer

Transfers involving peripherals are peripheral to peripheral and memory to/from peripheral

transfers. The routine is exported from the DMA driver. Here, synchronization issues are to

be handled by client 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. Transfers with peripherals always require you to

pass the configuration, so the slave pointer in the client structure must be non NULL.

A transfer is prepared by the following call.

chan:

is a pointer to DMA channel allocated to client.

sgl:

is a scatter list prepared by the client driver. Nodes of this scatter list

are configured with the address of memory or address of another peripherals

This enables the user to perform scatter-gather feature of DMA (i.e. a

single DMA transfer can transfer data to/from different memory buffers which

are not present continuously in memory).

sg_len:

number of scatterlist nodes in sgl.

direction:

if direction is DMA_TO_DEVICE then data is transferred to address

present in slave.tx_reg and if DMA_FROM_DEVICE then data is

transferred to address in sgl.

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. It must not be NULL for

successful preparation of DMA xfer. */

UM0851 Datasheet(PDF) 168 Page - STMicroelectronics

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