KnIoDmaCreate()

This function is declared in the coresrv/io/dma.h file.

Retcode KnIoDmaCreate(rtl_uint32_t order, rtl_size_t size, DmaAttr flags,

Handle *outRid);

This function registers and allocates a physical DMA buffer.

Input parameters:

• order is the minimum permissible order of DMA block allocation; the actual order of each block in the DMA buffer is chosen by the kernel (but will not be less than the specified order) and is indicated in the block handle; the order of a block determines the number of pages in it. For example, a block with an order of N consists of 2^N pages.
• size refers to the size of the DMA buffer, in bytes (must be a multiple of the page size); the sum of all sizes of allocated DMA blocks will be no less than the specified size.
• flags refers to DMA flags.

Output parameter outRid contains the handle of the allocated DMA buffer.

If successful, the function returns rcOk.

If a DMA buffer is no longer being used, it must be freed by using the KnIoClose() function.

Example

Retcode RegisterDmaMem(rtl_size_t size,

DmaAttr attr,

Handle *handle,

Handle *dmaHandle,

Handle *mappingHandle,

void **addr)

{

Retcode ret;

*handle = INVALID_HANDLE;

*dmaHandle = INVALID_HANDLE;

*mappingHandle = INVALID_HANDLE;

ret = KnIoDmaCreate(rtl_roundup_order(size >> PAGE_SHIFT),

size,

attr,

handle);

if (ret == rcOk) {

ret = KnIoDmaBegin(*handle, dmaHandle);

}

if (ret == rcOk) {

ret = KnIoDmaMap(*handle,

0,

size,

RTL_NULL,

VMM_FLAG_READ | VMM_FLAG_WRITE,

addr,

mappingHandle);

}

if (ret != rcOk) {

if (*mappingHandle != INVALID_HANDLE)

KnHandleClose(*mappingHandle);

if (*dmaHandle != INVALID_HANDLE)

KnHandleClose(*dmaHandle);

if (*handle != INVALID_HANDLE)

KnHandleClose(*handle);

}

return ret;

}