illumos: manual page: ddi_dma_alloc

DDI_DMA_ALLOC_HANDLE(9F) Kernel Functions for Drivers DDI_DMA_ALLOC_HANDLE(9F)

NAME

ddi_dma_alloc_handle - allocate DMA handle

SYNOPSIS

#include <sys/ddi.h>
#include <sys/sunddi.h>

int ddi_dma_alloc_handle(dev_info_t *dip, ddi_dma_attr_t *attr,
int (*callback) (caddr_t), caddr_t arg, ddi_dma_handle_t *handlep);

INTERFACE LEVEL

illumos DDI specific (illumos DDI).

PARAMETERS

dip
Pointer to the device's dev_info structure.

attr
Pointer to a DMA attribute structure for this device (see
ddi_dma_attr(9S)).

callback
The address of a function to call back later if resources
aren't available now. The following special function
addresses may also be used.

DDI_DMA_SLEEP
Wait until resources are available.

DDI_DMA_DONTWAIT
Do not wait until resources are available
and do not schedule a callback.

arg
Argument to be passed to a callback function, if such a
function is specified.

handlep
Pointer to the DMA handle to be initialized.

DESCRIPTION

ddi_dma_alloc_handle() allocates a new DMA handle. A DMA handle is an
opaque object used as a reference to subsequently allocated DMA
resources. ddi_dma_alloc_handle() accepts as parameters the device
information referred to by dip and the device's DMA attributes
described by a ddi_dma_attr(9S) structure. A successful call to
ddi_dma_alloc_handle() fills in the value pointed to by handlep. A DMA
handle must only be used by the device for which it was allocated and is
only valid for one I/O transaction at a time.

The callback function, callback, indicates how a caller wants to handle
the possibility of resources not being available. If callback is set to
DDI_DMA_DONTWAIT, then the caller does not care if the allocation fails,
and can handle an allocation failure appropriately. If callback is set
to DDI_DMA_SLEEP, then the caller wishes to have the allocation routines
wait for resources to become available. If any other value is set, and a
DMA resource allocation fails, this value is assumed to be a function to
call at a later time when resources may become available. When the
specified function is called, it is passed arg as an argument. The
specified callback function must return either DDI_DMA_CALLBACK_RUNOUT or
DDI_DMA_CALLBACK_DONE. DDI_DMA_CALLBACK_RUNOUT indicates that the
callback routine attempted to allocate DMA resources but failed to do so,
in which case the callback function is put back on a list to be called
again later. DDI_DMA_CALLBACK_DONE indicates either success at
allocating DMA resources or the driver no longer wishes to retry.

The callback function is called in interrupt context. Therefore, only
system functions that are accessible from interrupt context is
available. The callback function must take whatever steps necessary to
protect its critical resources, data structures, queues, and so forth.

When a DMA handle is no longer needed, ddi_dma_free_handle(9F) must be
called to free the handle.

RETURN VALUES

ddi_dma_alloc_handle() returns:

DDI_SUCCESS
Successfully allocated a new DMA handle.

DDI_DMA_BADATTR
The attributes specified in the ddi_dma_attr(9S)
structure make it impossible for the system to
allocate potential DMA resources.

DDI_DMA_NORESOURCES
No resources are available.

CONTEXT

ddi_dma_alloc_handle() can be called from user, kernel, or interrupt
context, except when callback is set to DDI_DMA_SLEEP, in which case it
can be called from user or kernel context only.