ddi_dma_req(9S)
NAME
ddi_dma_req - DMA Request structure
SYNOPSIS
#include <sys/ddidmareq.h>
INTERFACE LEVEL
Solaris DDI specific (Solaris DDI).
DESCRIPTION
A ddi_dma_req structure describes a request for DMA
resources. A driver can use it to describe forms of alloca-
tions and ways to allocate DMA resources for a DMA request.
STRUCTURE MEMBERS
ddi_dma_lim_t *dmar_limits; /* Caller's dma engine's */
/* constraints */
uint_t dmar_flags; /* Contains information for */
/* mapping routines */
int (*dmar_fp)(caddr_t); /* Callback function */
caddr_t dmar_arg; /* Callback function's argument */
ddi_dma_obj_t dmar_object; /* Description of the object */
/* to be mapped */
For the definition of the DMA limits structure, which
dmar_limits points to, see ddi_dma_lim_sparc(9S) or
ddi_dma_lim_x86(9S).
Valid values for dmar_flags are:
DDI_DMA_WRITE /* Direction memory --> IO */
DDI_DMA_READ /* Direction IO --> memory */
DDI_DMA_RDWR /* Both read and write */
DDI_DMA_REDZONE /* Establish an MMU redzone at end of mapping */
DDI_DMA_PARTIAL /* Partial mapping is allowed */
DDI_DMA_CONSISTENT /* Byte consistent access wanted */
DDI_DMA_SBUS_64BIT /* Use 64 bit capability on SBus */
DDI_DMA_WRITE, DDI_DMA_READ, and DDI_DMA_RDWR describe the
intended direction of the DMA transfer. Some implementations
might explicitly disallow DDI_DMA_RDWR.
DDI_DMA_REDZONE asks the system to establish a protected
red zone after the object. The DMA resource allocation func-
tions do not guarantee the success of this request, as some
implementations might not have the hardware ability to sup-
port it.
DDI_DMA_PARTIAL lets the system know that the caller can
accept partial mapping. That is, if the size of the object
exceeds the resources available, the system allocates only a
portion of the object and returns status indicating this
partial allocation. At a later point, the caller can use
ddi_dma_curwin(9F) and ddi_dma_movwin(9F) to change the
valid portion of the object that has resources allocated.
DDI_DMA_CONSISTENT gives a hint to the system that the
object should be mapped for byte consistent access. Normal
data transfers usually use a streaming mode of operation.
They start at a specific point, transfer a fairly large
amount of data sequentially, and then stop, usually on an
aligned boundary. Control mode data transfers for memory-
resident device control blocks (for example, Ethernet mes-
sage descriptors) do not access memory in such a sequential
fashion. Instead, they tend to modify a few words or bytes,
move around and maybe modify a few more.
Many machine implementations make this non-sequential memory
access difficult to control in a generic and seamless
fashion. Therefore, explicit synchronization steps using
ddi_dma_sync(9F) or ddi_dma_free(9F) are required to make
the view of a memory object shared between a CPU and a DMA
device consistent. However, proper use of the
DDI_DMA_CONSISTENT flag can create a condition in which a
system will pick resources in a way that makes these syn-
chronization steps are as efficient as possible.
DDI_DMA_SBUS_64BIT tells the system that the device can per-
form 64-bit transfers on a 64-bit SBus. If the SBus does not
support 64-bit data transfers, data will be transferred in
32-bit mode.
The callback function specified by the member dmar_fp indi-
cates how a caller to one of the DMA resource allocation
functions wants to deal with the possibility of resources
not being available. (See ddi_dma_setup(9F).) If dmar_fp is
set to DDI_DMA_DONTWAIT, then the caller does not care if
the allocation fails, and can deal with an allocation
failure appropriately. Setting dmar_fp to DDI_DMA_SLEEP
indicates the caller wants 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 later, when resources
become available. When the specified function is called, it
is passed the value set in the structure member dmar_arg.
The specified callback function must return either:
0 Indicating that it attempted to allocate a DMA
resource but failed to do so, again, in which
case the callback function will be put back on a
list to be called again later.
1 Indicating either success at allocating DMA
resources or that it no longer wants to retry.
The callback function is called in interrupt context. There-
fore, only system functions and contexts that are accessible
from interrupt context are available. The callback function
must take whatever steps necessary to protect its critical
resources, data structures, and queues.
It is possible that a call to ddi_dma_free(9F), which frees
DMA resources, might cause a callback function to be called
and, unless some care is taken, an undesired recursion can
occur. This can cause an undesired recursive
mutex_enter(9F), which makes the system panic.
dmar_object Structure
The dmar_object member of the ddi_dma_req structure is
itself a complex and extensible structure:
uint_t dmao_size; /* size, in bytes, of the object */
ddi_dma_atyp_t dmao_type; /* type of object */
ddi_dma_aobj_t dmao_obj; /* the object described */
The dmao_size element is the size, in bytes, of the object
resources allocated for DMA.
The dmao_type element selects the kind of object described
by dmao_obj. It can be set to DMA_OTYP_VADDR, indicating
virtual addresses.
The last element, dmao_obj, consists of the virtual address
type:
struct v_address virt_obj;
It is specified as:
struct v_address {
caddr_t v_addr; /* base virtual address */
struct as *v_as; /* pointer to address space */
void *v_priv; /* priv data for shadow I/O */
};
SEE ALSO
ddi_dma_addr_setup(9F), ddi_dma_buf_setup(9F),
ddi_dma_curwin(9F), ddi_dma_free(9F), ddi_dma_movwin(9F),
ddi_dma_setup(9F), ddi_dma_sync(9F), mutex(9F)
Writing Device Drivers
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