man pages section 9: DDI and DKI Properties and Data Structures

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Updated: July 2014



ddi_dma_lim_x86 - x86 DMA limits structure


#include <sys/ddidmareq.h>

Interface Level

Solaris x86 DDI specific (Solaris x86 DDI). This interface is obsolete.


A ddi_dma_lim structure describes in a generic fashion the possible limitations of a device or its DMA engine. This information is used by the system when it attempts to set up DMA resources for a device. When the system is requested to perform a DMA transfer to or from an object, the request is broken up, if necessary, into multiple sub-requests. Each sub–request conforms to the limitations expressed in the ddi_dma_lim structure.

This structure should be filled in by calling the routine ddi_dmae_getlim(9F). This routine sets the values of the structure members appropriately based on the characteristics of the DMA engine on the driver's parent bus. If the driver has additional limitations, it can further restrict some of the values in the structure members. A driver should not relax any restrictions imposed by ddi_dmae_getlim().

Structure Members

uint_t  dlim_addr_lo;  /* low range of 32 bit 
                                        addressing capability */
uint_t  dlim_addr_hi;  /* inclusive upper bound of 
                          addressing capability */
uint_t  dlim_minxfer;  /* minimum effective dma transfer size */
uint_t  dlim_version;  /* version number of structure */
uint_t  dlim_adreg_max; /* inclusive upper bound of 
                            incrementing addr reg */
uint_t  dlim_ctreg_max; /* maximum transfer count minus one */
uint_t  dlim_granular; /* granularity (and min size) of 
                          transfer count */
short  dlim_sgllen;    /* length of DMA scatter/gather list */
uint_t  dlim_reqsize;  /* maximum transfer size in bytes of 
                          a single I/O */

The dlim_addr_lo and dlim_addr_hi fields specify the address range that the device's DMA engine can access. The dlim_addr_lo field describes the lower 32–bit boundary of the device's DMA engine. The dlim_addr_hi member describes the inclusive, upper 32–bit boundary. The system allocates DMA resources in a way that the address for programming the device's DMA engine will be within this range. For example, if your device can access the whole 32–bit address range, you can use [0,0xFFFFFFFF]. See ddi_dma_cookie(9S) or ddi_dma_segtocookie(9F).

The dlim_minxfer field describes the minimum effective DMA transfer size (in units of bytes), which must be a power of two. This value specifies the minimum effective granularity of the DMA engine and describes the minimum amount of memory that can be touched by the DMA transfer. As a resource request is handled by the system, the dlim_minxfer value can be modified. This modification is contingent upon the presence (and use) of I/Ocaches and DMA write buffers between the DMA engine and the object that DMA is being performed on. After DMA resources have been allocated, you can retrieve the resultant minimum transfer value using ddi_dma_devalign(9F).

The dlim_version field specifies the version number of this structure. Set this field to DMALIM_VER0.

The dlim_adreg_max field describes an inclusive upper bound for the device's DMA engine address register. This bound handles a fairly common case where a portion of the address register is simply a latch rather than a full register. For example, the upper 16 bits of a 32–bit address register might be a latch. This splits the address register into a portion that acts as a true address register (lower 16 bits) for a 64–kilobyte segment and a latch (upper 16 bits) to hold a segment number. To describe these limits, you specify 0xFFFF in the dlim_adreg_max structure member.

The dlim_ctreg_max field specifies the maximum transfer count that the DMA engine can handle in one segment or cookie. The limit is expressed as the maximum count minus one. This transfer count limitation is a per-segment limitation. Because the limitation is used as a bit mask, it must be one less than a power of two.

The dlim_granular field describes the granularity of the device's DMA transfer ability, in units of bytes. This value is used to specify, for example, the sector size of a mass storage device. DMA requests are broken into multiples of this value. If there is no scatter/gather capability, then the size of each DMA transfer will be a multiple of this value. If there is scatter/gather capability, then a single segment cannot be smaller than the minimum transfer value, but can be less than the granularity. However, the total transfer length of the scatter/gather list is a multiple of the granularity value.

The dlim_sgllen field specifies the maximum number of entries in the scatter/gather list. This value is the number of segments or cookies that the DMA engine can consume in one I/O request to the device. If the DMA engine has no scatter/gather list, set this field to one.

The dlim_reqsize field describes the maximum number of bytes that the DMA engine can transmit or receive in one I/O command. This limitation is only significant if it is less than ( dlim_ctreg_max +1) * dlim_sgllen. If the DMA engine has no particular limitation, set this field to 0xFFFFFFFF.


See attributes(5) for descriptions of the following attributes:

Interface Stability

See also

ddi_dmae(9F), ddi_dma_addr_setup(9F) , ddi_dma_buf_setup(9F), ddi_dma_devalign (9F), ddi_dma_segtocookie(9F), ddi_dma_setup(9F), ddi_dma_cookie(9S), ddi_dma_lim_sparc(9S), ddi_dma_req(9S)