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ddi_dma_req(9s)
ddi_dma_req(9S) Kernel & Driver Data Structures ddi_dma_req(9S)
NAME
ddi_dma_req - DMA Request structure
SYNOPSIS
#include <sys/ddidmareq.h>
INTERFACE LEVEL
Solaris DDI specific (Solaris DDI). This interface is obsolete.
DESCRIPTION
A ddi_dma_req structure describes a request for DMA resources. A driver
can use it to describe forms of allocations and ways to allocate DMA
resources for a DMA request.
STRUCTURE MEMBERS
ddi_dma_lim_t *dmar_limits; /* Caller's dma engine
constraints */
uint_t dmar_flags; /* Contains info for
mapping routines */
int (*dmar_fp)(caddr_t);/* Callback function */
caddr_t dmar_arg; /* Callback function's argument */
ddi_dma_obj_t dmar_object; /* Descrip. of 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 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 di‐
rection of the DMA transfer. Some implementations might explicitly dis‐
allow DDI_DMA_RDWR.
DDI_DMA_REDZONE asks the system to establish a protected red zone after
the object. The DMA resource allocation functions do not guarantee the
success of this request, as some implementations might not have the
hardware ability to support 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 re‐
turns 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 de‐
vice control blocks (for example, Ethernet message descriptors) do not
access memory in such a sequential fashion. Instead, they tend to mod‐
ify 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, ex‐
plicit 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_CONSIS‐
TENT flag can create a condition in which a system will pick resources
in a way that makes these synchronization steps are as efficient as
possible.
DDI_DMA_SBUS_64BIT tells the system that the device can perform 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 indicates 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 al‐
location failure appropriately. Setting dmar_fp to DDI_DMA_SLEEP indi‐
cates the caller wants to have the allocation routines wait for re‐
sources to become available. If any other value is set, and a DMA re‐
source 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. Therefore, only
system functions and contexts that are accessible from interrupt con‐
text are available. The callback function must take whatever steps nec‐
essary to protect its critical resources, data structures, and queues.
It is possible that a call to ddi_dma_free(9F), which frees DMA re‐
sources, might cause a callback function to be called and, unless some
care is taken, an undesired recursion can occur. This can cause an un‐
desired 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 */
};
ATTRIBUTES
See attributes(7) for descriptions of the following attributes:
tab() box; cw(2.75i) |cw(2.75i) lw(2.75i) |lw(2.75i) ATTRIBUTE TYPEAT‐
TRIBUTE VALUE _ Interface StabilityObsolete
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), dmao_get_size(9F), mutex(9F)
Writing Device Drivers in Oracle Solaris 11.4
Oracle Solaris 11.4 10 Nov 2016 ddi_dma_req(9S)