NAME

ddi_dma_mem_alloc - allocate memory for DMA transfer

SYNOPSIS

#include <sys/ddi.h>
#include <sys/sunddi.h>
int ddi_dma_mem_alloc(ddi_dma_handle_t handle, size_t length,


     const ddi_device_acc_attr_t *accattrp, uint_t flags,


     int (*waitfp) (caddr_t), caddr_t arg, caddr_t *kaddrp,


     size_t *real_length, ddi_acc_handle_t *handlep);

INTERFACE LEVEL

illumos DDI specific (illumos DDI).

PARAMETERS

handle

The DMA handle previously allocated by a call to ddi_dma_alloc_handle(9F).

length

The length in bytes of the desired allocation.

accattrp

Pointer to a ddi_device_acc_attr() structure of the device. See ddi_device_acc_attr(9S). The value in devacc_attr_dataorder is ignored in the current release. The value in devacc_attr_endian_flags is meaningful on the SPARC architecture only.

flags

Used to determine the data transfer mode and/or the cache attribute.

Possible values of the data transfer are:

DDI_DMA_STREAMING

Sequential, unidirectional, block-sized, and block-aligned transfers.

DDI_DMA_CONSISTENT

Nonsequential transfers of small objects.

Possible values of the cache attribute are:

IOMEM_DATA_CACHED

The CPU can cache the data it fetches and push it to memory at a later time. This is the default attribute that is used if no cache attributes are specified.

IOMEM_DATA_UC_WR_COMBINE

The CPU never caches the data, but writes can occur out of order or can be combined. Reordering is implied.

If IOMEM_DATA_UC_WR_COMBINE is specified but not supported, IOMEM_DATA_UNCACHED is used instead.

IOMEM_DATA_UNCACHED

The CPU never caches data, but has uncacheable access to memory. Strict ordering is implied.

The cache attributes are mutually exclusive. Any combination of the values leads to a failure. On the SPARC architecture, only IOMEM_DATA_CACHED is meaningful. Others lead to a failure.

waitfp

The address of a function to call back later if resources are not available now. The callback function indicates how a caller wants to handle the possibility of resources not being available. If callback is set to DDI_DMA_DONTWAIT, the caller does not care if the allocation fails, and can handle an allocation failure appropriately. If callback is set to DDI_DMA_SLEEP, 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 the address of a function to be called when resources become available. When the specified function is called, arg is passed to it 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 function attempted to allocate DMA resources but failed. In this case, the callback function is put back on a list to be called again later. DDI_DMA_CALLBACK_DONE indicates that either the allocation of DMA resources was successful or the driver no longer wishes to retry. The callback function is called in interrupt context. Therefore, only system functions accessible from interrupt context are available.

The callback function must take whatever steps are necessary to protect its critical resources, data structures, queues, and so on.

arg

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

kaddrp

On successful return, kaddrp points to the allocated memory.

real_length

The amount of memory, in bytes, allocated. Alignment and padding requirements may require ddi_dma_mem_alloc() to allocate more memory than requested in length.

handlep

Pointer to a data access handle.

DESCRIPTION

The ddi_dma_mem_alloc() function allocates memory for DMA transfers to or from a device. The allocation will obey the alignment, padding constraints and device granularity as specified by the DMA attributes (see ddi_dma_attr(9S)) passed to ddi_dma_alloc_handle(9F) and the more restrictive attributes imposed by the system.

The flags parameter should be set to DDI_DMA_STREAMING if the device is doing sequential, unidirectional, block-sized, and block-aligned transfers to or from memory. The alignment and padding constraints specified by the minxfer and burstsizes fields in the DMA attribute structure, ddi_dma_attr(9S) (see ddi_dma_alloc_handle(9F)) will be used to allocate the most effective hardware support for large transfers. For example, if an I/O transfer can be sped up by using an I/O cache, which has a minimum transfer of one cache line, ddi_dma_mem_alloc() will align the memory at a cache line boundary and it will round up real_length to a multiple of the cache line size.

The flags parameter should be set to DDI_DMA_CONSISTENT if the device accesses memory randomly, or if synchronization steps using ddi_dma_sync(9F) need to be as efficient as possible. I/O parameter blocks used for communication between a device and a driver should be allocated using DDI_DMA_CONSISTENT.

The device access attributes are specified in the location pointed by the accattrp argument (see ddi_device_acc_attr(9S)).

The data access handle is returned in handlep. handlep is opaque - drivers may not attempt to interpret its value. To access the data content, the driver must invoke ddi_get8(9F) or ddi_put8(9F) (depending on the data transfer direction) with the data access handle.

DMA resources must be established before performing a DMA transfer by passing kaddrp and real_length as returned from ddi_dma_mem_alloc() and the flag DDI_DMA_STREAMING or DDI_DMA_CONSISTENT to ddi_dma_addr_bind_handle(9F). In addition, to ensure the consistency of a memory object shared between the CPU and the device after a DMA transfer, explicit synchronization steps using ddi_dma_sync(9F) or ddi_dma_unbind_handle(9F) are required.

RETURN VALUES

The ddi_dma_mem_alloc() function returns:

DDI_SUCCESS

Memory successfully allocated.

DDI_FAILURE

Memory allocation failed.

CONTEXT

The ddi_dma_mem_alloc() function can be called from user, interrupt, or kernel context except when waitfp is set to DDI_DMA_SLEEP, in which case it cannot be called from interrupt context.

WARNINGS

If DDI_NEVERSWAP_ACC is specified, memory can be used for any purpose; but if either endian mode is specified, you must use ddi_get/put* and never anything else.