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


ddi_dmae, ddi_dmae_alloc, ddi_dmae_release, ddi_dmae_prog,
ddi_dmae_disable, ddi_dmae_enable, ddi_dmae_stop, ddi_dmae_getcnt,
ddi_dmae_1stparty, ddi_dmae_getattr - system DMA engine functions


int ddi_dmae_alloc(dev_info_t *dip, int chnl, int (*callback) (caddr_t),
caddr_t arg);

int ddi_dmae_release(dev_info_t *dip, int chnl);

int ddi_dmae_prog(dev_info_t *dip, struct ddi_dmae_req *dmaereqp,
ddi_dma_cookie_t *cookiep, int chnl);

int ddi_dmae_disable(dev_info_t *dip, int chnl);

int ddi_dmae_enable(dev_info_t *dip, int chnl);

int ddi_dmae_stop(dev_info_t *dip, int chnl);

int ddi_dmae_getcnt(dev_info_t *dip, int chnl, int *countp);

int ddi_dmae_1stparty(dev_info_t *dip, int chnl);

int ddi_dmae_getattr(dev_info_t *dip, ddi_dma_attr_t *attrp);


illumos DDI specific (illumos DDI).


A dev_info pointer that identifies the device.

A DMA channel number. On ISA buses this number must be 0, 1,
2, 3, 5, 6, or 7.

The address of a function to call back later if resources are
not currently available. The following special function
addresses may also be used:

Wait until resources are available.

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

Argument to be passed to the callback function, if specified.

A pointer to a DMA engine request structure. See

A pointer to a ddi_dma_cookie(9S) object, which contains the
address and count.

A pointer to an integer that will receive the count of the
number of bytes not yet transferred upon completion of a DMA

A pointer to a DMA attribute structure. See


There are three possible ways that a device can perform DMA engine

Bus master DMA
If the device is capable of acting as a true bus
master, then the driver should program the device's
DMA registers directly and not make use of the DMA
engine functions described here. The driver should
obtain the DMA address and count from

Third-party DMA
This method uses the system DMA engine that is
resident on the main system board. In this model, the
device cooperates with the system's DMA engine to
effect the data transfers between the device and
memory. The driver uses the functions documented here,
except ddi_dmae_1stparty(), to initialize and program
the DMA engine. For each DMA data transfer, the driver
programs the DMA engine and then gives the device a
command to initiate the transfer in cooperation with
that engine.

First-party DMA
Using this method, the device uses its own DMA bus
cycles, but requires a channel from the system's DMA
engine. After allocating the DMA channel, the
ddi_dmae_1stparty() function may be used to perform
whatever configuration is necessary to enable this

The ddi_dmae_alloc() function is used to acquire a DMA channel of the
system DMA engine. ddi_dmae_alloc() allows only one device at a time to
have a particular DMA channel allocated. It must be called prior to any
other system DMA engine function on a channel. If the device allows the
channel to be shared with other devices, it must be freed using
ddi_dmae_release() after completion of the DMA operation. In any case,
the channel must be released before the driver successfully detaches. See
detach(9E). No other driver may acquire the DMA channel until it is

If the requested channel is not immediately available, the value of
callback determines what action will be taken. If the value of callback
is DDI_DMA_DONTWAIT, ddi_dmae_alloc() will return immediately. The value
DDI_DMA_SLEEP will cause the thread to sleep and not return until the
channel has been acquired. Any other value is assumed to be a callback
function address. In that case, ddi_dmae_alloc() returns immediately, and
when resources might have become available, the callback function is
called (with the argument arg) from interrupt context. When the callback
function is called, it should attempt to allocate the DMA channel again.
If it succeeds or no longer needs the channel, it must return the value
DDI_DMA_CALLBACK_DONE. If it tries to allocate the channel but fails to
do so, it must return the value DDI_DMA_CALLBACK_RUNOUT. In this case,
the callback function is put back on a list to be called again later.

The ddi_dmae_prog() function programs the DMA channel for a DMA transfer.
The ddi_dmae_req structure contains all the information necessary to set
up the channel, except for the memory address and count. Once the channel
has been programmed, subsequent calls to ddi_dmae_prog() may specify a
value of NULL for dmaereqp if no changes to the programming are required
other than the address and count values. It disables the channel prior to
setup, and enables the channel before returning. The DMA address and
count are specified by passing ddi_dmae_prog() a DMA cookie. Other DMA
engine parameters are specified by the DMA engine request structure
passed in through dmaereqp. The fields of that structure are documented
in ddi_dmae_req(9S).

Before using ddi_dmae_prog(), you must allocate system DMA resources
using DMA setup functions such as ddi_dma_mem_alloc(9F).
ddi_dma_addr_bind_handle(9F) can then be used to retrieve a cookie which
contains the address and count. Then this cookie is passed to

The ddi_dmae_disable() function disables the DMA channel so that it no
longer responds to a device's DMA service requests.

The ddi_dmae_enable() function enables the DMA channel for operation.
This may be used to re-enable the channel after a call to
ddi_dmae_disable(). The channel is automatically enabled after successful
programming by ddi_dmae_prog().

The ddi_dmae_stop() function disables the channel and terminates any
active operation.

The ddi_dmae_getcnt() function examines the count register of the DMA
channel and sets *countp to the number of bytes remaining to be
transferred. The channel is assumed to be stopped.

In the case of ISA buses, ddi_dmae_1stparty() configures a channel in the
system's DMA engine to operate in a ``slave'' (``cascade'') mode.

When operating in ddi_dmae_1stparty() mode, the DMA channel must first
be allocated using ddi_dmae_alloc() and then configured using
ddi_dmae_1stparty(). The driver then programs the device to perform the
I/O, including the necessary DMA address and count values obtained from
the ddi_dma_cookie(9S).

The ddi_dmae_getattr() function fills in the DMA attribute structure,
pointed to by attrp, with the DMA attributes of the system DMA engine.
Drivers for devices that perform their own bus mastering or use first-
party DMA must create and initialize their own DMA attribute structures;
they should not use ddi_dmae_getattr(). The DMA attribute structure must
be passed to the DMA resource allocation functions to provide the
information necessary to break the DMA request into DMA windows and DMA
cookies. See ddi_dma_cookie_iter(9F) and ddi_dma_getwin(9F).


Upon success, for all of these routines.

May be returned due to invalid arguments.

May be returned by ddi_dmae_alloc() if the
requested resources are not available and the
value of dmae_waitfp is not DDI_DMA_SLEEP.


If ddi_dmae_alloc() is called from interrupt context, then its
dmae_waitfp argument and the callback function must not have the value
DDI_DMA_SLEEP. Otherwise, all these routines can be called from user,
interrupt, or kernel context.


See attributes(7) for descriptions of the following attributes:

|Architecture | x86 |


isa(5), attributes(7), ddi_dma_addr_bind_handle(9F),
ddi_dma_buf_setup(9F), ddi_dma_cookie_iter(9F), ddi_dma_getwin(9F),
ddi_dma_mem_alloc(9F), ddi_dma_attr(9S), ddi_dma_cookie(9S),

January 18, 2020 DDI_DMAE(9F)