Index for Section 9

Alphabetical listing for D

Bottom of page

dma_put_curr_sgentry(9r)
NAME
  dma_put_curr_sgentry - General: Puts a new bus address/byte count pair in
  the linked list of sg_entry structures

SYNOPSIS
  #include <io/common/devdriver.h>


  int dma_put_curr_sgentry(
	  dma_handle_t dma_handle,
	  sg_entry_t sg_entryp );

ARGUMENTS
  dma_handle
      Specifies a handle to DMA resources associated with the mapping of an
      in-memory I/O buffer onto a controller's I/O bus. This handle provides
      the information to access bus address/byte count pairs. A bus
      address/byte count pair is represented by the ba and bc members of an
      sg_entry structure pointer. Device driver writers can view the DMA
      handle as the tag to the allocated system resources needed to perform a
      DMA operation.

  sg_entryp
      Specifies a pointer to the sg_entry structure that contains the bus
      address/byte count values to replace the corresponding bus address/byte
      count of the sg_entry structure associated with this DMA handle. You
      set the bus address/byte count in the ba and bc members of the sg_entry
      structure and then pass its address to dma_put_curr_sgentry.

DESCRIPTION
  The dma_put_curr_sgentry interface puts new bus address/byte count values
  into the ba and bc members for the existing bus address/byte count pair
  pointed to by the DMA handle passed in by you. This interface enables
  device drivers to patch an existing bus address/byte count pair due to an
  unexpected interruption in a DMA transfer. A bus address/byte count pair is
  represented by the ba and bc members of an sg_entry structure pointer.

  This interface is useful for DMA engines that do not have total control of
  a DMA transfer. For example, a SCSI device doing an unexpected disconnect
  in the middle of a block transfer can interrupt a SCSI controller. Such a
  disconnect can require the driver to do one or more patches to the list of
  bus address/byte count pairs in order to restart the DMA transfer (without
  starting from the beginning of the list). Device drivers call the
  dma_put_curr_sgentry and dma_put_prev_sgentry interfaces to accomplish
  these patch operations.  Typically, only buses that do not have byte
  atomicity transfers (for example, the TURBOchannel bus on Alpha CPUs)
  require these patch operations.



RETURN VALUES
  Upon successful completion, dma_put_curr_sgentry returns the value 1.
  Otherwise, dma_put_curr_sgentry returns the value zero (0) to indicate a
  failure. This failure indicates that the index into the DMA handle points
  past the end of the last bus address/byte count pair. The DMA handle can
  point past the end of the valid portion of the list when the previous call
  to dma_get_next_sgentry returned the pointer to the DMA handle associated
  with the last byte address/byte count pair.

EXAMPLE
  See Writing Device Drivers: Tutorial for a code example of the
  dma_put_curr_sgentry interface.

SEE ALSO
  Kernel Interfaces: dma_get_curr_sgentry(9r), dma_get_next_sgentry(9r),
  dma_put_prev_sgentry(9r)

  Data Structures: sg_entry(9s)

Index for Section 9

Alphabetical listing for D

Top of page