scgth(D4)

scgth -- DMA scatter/gather list structure

Synopsis

   #include <sys/types.h>
   #include <sys/kmem.h>
   #include <sys/scgth.h>
   #include <sys/ddi.h>
   
   typedef struct {
   	union {
   		scgth_el32_t el32;
   		scgth_el64_t el64;
   	} sg_elem;
   	union {
   		scgth_el32_t ea32;
   		scgth_el64_t ea64;
   	} sg_el_addr;
   	uchar_t sg_nelem;
   	uchar_t sg_format;
   } scgth_t;
   

   typedef struct {
   	u_int32_t	sg_base;
   	u_int32_t	sg_size;
   } scgth_el32_t;
   

   typedef struct {
   	u_int32_t	sg_base[2];
   	u_int32_t	sg_size;
   	u_int32_t	_sg_reserved;
   } scgth_el64_t;

Description

The scgth structure describes a scatter/gather list, used for performing DMA from an I/O device to mainstore memory. A scatter/gather list contains a sequence of (address, length) pairs identifying one or more physically discontiguous pieces of memory. The addresses are physical addresses appropriate for use by the device's DMA engine.

Structure members

sg_elem

array of scatter/gather elements, allocated in memory that meets the constraints specified by an appropriate physreq(D4) structure (for example, as specified by the bcb argument to the buf_breakup(D3) function).

sg_el_addr

This ``meta'' element, in the same format as a scatter/gather list element, describes the physical memory containing the scatter/gather list itself. This can be used to load the DMA engine with the location of the scatter/gather list.

sg_nelem

number of elements in the sg_elem array

sg_format

Data format to be used, based on the value of the phys_dmasize member of the physreq(D4) structure. Valid values are:

SCGTH32: Scatter/gather list is in 32-bit format; the el32 and ea32 union members are used. Used if the value of phys_dmasize is less than or equal to 32.
SCGTH64: Scatter/gather list is in 64-bit format; the el64 and ea64 union members are used. Used if the value of phys_dmasize is greater than 32.

sg_base

base physical address for the scatter/gather element. For the SCGTH64 format, sg_base[0] holds the least significant 32 bits of information and sg_base[1] holds the most significant 32 bits.

sg_size

size, in bytes, for the scatter/gather element.

_sg_reserved

reserved for future use. Do not use.

Usage

The scgth structure is passed to the buf_breakup(D3) or the msgscgth(D3str) function to implement scatter/gather functionality.

Hardware applicability

All

Version applicability

ddi: 8, 8mp

Differences between versions

References

buf(D4), buf_breakup(D3), msgscgth(D3str), physreq(D4), scgth_free(D3)

``Scatter/gather operations'' in HDK Technical Reference