d_alloc_dmamem Kernel Service
Purpose
Allocates an area of dma-able
memory.
Syntax
void *
d_alloc_dmamem(d_handle_t device_handle, size_t size,int align)
Description
Exported, documented kernel service supported
on PCI-based systems only. The d_alloc_dmamem kernel service
allocates an area of dma-able
memory which satisfies the constraints
associated with a DMA handle, specified via the device_handle
parameter. The constraints (such as need for contiguous physical
pages or need for 32-bit physical address) are intended to guarantee
that a given adapter will be able to access the physical pages associated
with the allocated memory. A driver associates such constraints with
a dma handle via the flags parameter on its d_map_init call.
The area to be allocated is the number of bytes in length specified by the size parameter, and is aligned on the byte boundary specified by the align parameter. The align parameter is actually the log base 2 of the desired address boundary. For example, an align value of 12 requests that the allocated area be aligned on a 4096 byte boundary.
d_alloc_dmamem is appropriate to be used for long-term mappings. Depending on the system configuration and the constraints encoded in the device_handle, the underlying storage will come from either the real_heap (rmalloc service) or pinned_heap (xmalloc service).
- The d_free_dmamem service should be called to free allocation from a previous d_alloc_dmamem call.
- The d_alloc_dmamem kernel service can be called from the process environment only.
Parameters
| Item | Description |
|---|---|
| device_handle | Indicates the dma handle. |
| align | Specifies alignment characteristics. |
| size_t size | Specifies number of bytes to allocate. |
Return Values
| Item | Description |
|---|---|
| Address of allocated area | Indicates that d_alloc_dmamem was successful. |
| NULL | Requested memory could not be allocated. |