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dma_kmap_buffer(9r)
NAME
  dma_kmap_buffer - General: Returns a kernel segment (kseg) address of a DMA
  buffer

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


  vm_offset_t dma_kmap_buffer(
	  dma_handle_t dma_handle,
	  u_long offset );

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.

  offset
      Specifies a byte count offset from the virtual address passed as the
      virt_addr argument of the dma_map_load interface. This virtual address
      specifies the beginning of a process's (or kernel) buffer that a DMA
      transfer operation is done to or from. A device driver determines the
      smallest DMA transfer size by calling the dma_min_boundary interface.
      The offset specifies the number of bytes a DMA engine moved. This
      number is less than the number of bytes the dma_map_load interface
      loaded.

DESCRIPTION
  The dma_kmap_buffer interface takes an offset variable and returns a kseg
  address. The device driver can use this kseg address to copy and save the
  data at the offset in the buffer.

  A device driver calls dma_kmap_buffer when the following occurs:

    ·  A DMA device on a CPU or bus interrupts a transfer before the full
       transfer has completed

    ·  The value returned by dma_min_boundary is greater than 1

    ·  The transfer is interrupted within the region of the value returned by
       dma_min_boundary.

  For example, a SCSI device performs a disconnect in the second byte of a
  longword on a TURBOchannel-based SCSI subsystem. The device driver uses the
  kseg address to read the valid data transferred so far, saves it in a
  dma_min_boundary sized buffer, and merges it back into the DMA buffer once
  the rest of the transfer has completed.




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

RETURN VALUES
  Upon successful completion, dma_kmap_buffer returns a kseg address of the
  byte offset pointed to by the addition of the following two values:

       virt_addr + offset

  where:

    ·  virt_addr is the virtual address passed to the virt_addr argument of
       dma_map_load

    ·  offset is the offset passed to the offset argument of dma_kmap_buffer

  The dma_kmap_buffer interface returns the value zero (0) to indicate
  failure to retrieve the kseg address.

SEE ALSO
  Kernel Interfaces: dma_map_load(9r), dma_min_boundary(9r)

  Data Structures: sg_entry(9s)

Index for Section 9

Alphabetical listing for D

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