UM0851 datasheet(165/245 Pages) STMICROELECTRONICS

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UM0851

Accelerator engine device drivers

Doc ID 16604 Rev 2

165/245

Client registration

A client can register with the framework by using the following call:

dma_async_client_register(&dma_client1);

/* dma_client1 is an instance of struct dma_client present in

include/linux/dmaengine.h */

struct dma_client {

dma_event_callback

event_callback;

/* Function ptr for DMA framework purposes

(Mandatory). */

dma_cap_mask_t cap_mask;

/* Capability of the DMA Channel to be

requested, a value of zero corresponds to

any capability (Mandatory) */

struct dma_slave

*slave;

/* Data for preparing slave transfer. Must

be non-NULL if the DMA_SLAVE capability is

requested (Optional) */

struct list_head

global_node;

/* list_head for global dma_client_list

(Not for user driver) */

};

/* CAP can be one of DMA_MEMCPY (memory to memory), DMA_MEMSET(memory to memory),

DMA_SLAVE(peripheral to peripheral or memory to/from peripheral).

/* Prototype of this event_callback. */

static enum dma_state_client dma_event(struct dma_client *client, struct dma_chan

*chan, enum dma_state state);

/* cap_mask can be set using following function */

dma_cap_set(CAP, dma_client1.cap_mask);

After registering the client, you must request the DMA channels for transferring data. This

can be done using following call:

dma_async_client_chan_request(&dma_client1);

The DMA framework calls the dma_event() function twice, once for channel allocation and

once for channel removal. The value of enum dma_state state is:

●

DMA_RESOURCE_AVAILABLE during channel allocation, and

●

DMA_RESOURCE_REMOVED during channel removal.

You have to check the value of the state variable in dma_event() to determine the cause of

the function call.

During channel allocation, dma_event() is called for every free DMA channel available that

satisfies the capability requested by the client. This callback is called until you return

DMA_NAK from the dma_event() function. Suppose there are 8 DMA channels available

and you need only three of them, then you must return DMA_ACK on the first three calls to

event_callback() and return DMA_NAK on the fourth call. In addition, you must save all the

struct dma_chan *chan parameters passed to event_callback(), chan is a pointer to the

DMA channel which is currently allocated to the client.

During channel removal, dma_event() is called for every DMA channel allocated to the

client. You must return DMA_ACK for the channels you want to free.

UM0851 Datasheet(PDF) 165 Page - STMicroelectronics

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