dma_mapalloc(D3X)

NAME
     dma_mapalloc - allocate a DMA map

SYNOPSIS
     #include "sys/types.h"
     #include "sys/sema.h"
     #include "sys/dmamap.h"

     dmamap_t *dma_mapalloc(int type,int adapter, int num_pages,int flags);

   Arguments
     type Must be either DMA_A32VME or DMA_A24VME depending on the transfer
          desired.  (The DMA_SCSI type is reserved for exclusive use by the
          SCSI host adapter driver.)

     adapter
          Specifies the I/O adapter to use for setting up the mapping This
          should be set to the I/O bus adapter number to which the device
          doing DMA is attached to.

     num_pages
          Specifies the maximum number of mapping registers to allocate.
          Mapping registers are responsible for translating the addresses that
          appear on the I/O bus to a format that could be used internally
          within a system.  On current Silicon Graphics systems, each mapping
          register is capable of mapping a page of length 4096 bytes on the
          I/O bus to a set of consecutive addresses on system memory.  This is
          true regardless of the system page size.  The number of bytes each
          mapping register is capable of mapping could change in future
          systems.  In order to keep the device driver platform independent,
          use of the macro io_btoc is recommended to calculate the num_pages
          parameter for required length of mapping.  You need to allocate an
          extra page for non-page aligned transfers-for example, a transfer of
          4096 bytes starting at a non-aligned address actually requires two
          mapping registers.

     flags
          Reserved for future development.  For now, you should always set it
          to 0.

DESCRIPTION
     dma_mapalloc allocates DMA mapping registers on multiprocessor models and
     returns a pointer to a structure, of type dmamap_t, for later use by the
     mapping routine dma_map.  You need DMA maps to access main memory through
     VME A24 space.  In addition, because DMA maps give you the ability to
     perform transfers to non-contiguous physical memory, you also want them
     for A32 access.

     Use dma_mapfree to free the DMA mapping registers and other resources
     associated with a given map.
     VME adapter number to which a device is attached is available at edtinit
     time via e_adap field in edt structure.  It is also possible to get this
     number by using the function vme_adapter(D3X).

     This call can block (it calls psema) if no maps are available, so it must
     never be called at interrupt time.

     On Challenge and Onyx systems, the maximum amount of address space that
     can be mapped for DMA by A32 VME devices is 64MB by default.  This can be
     changed by modifying the systune variable nvme32_dma.  The value of
     nvme32_dma is the maximum amount of address space (in megabytes) that may
     be allocated for A32 VME devices.  The default value for nvme32_dma is 64
     (corresponding to the standard limit of 64MB of address space).
     nvme32_dma must be a power of 2 and may not exceed 512 (meaning 512MB).
     If a value larger than 512 is specified, it will be forced back down to
     512.  If the value is not a power of 2, it will be rounded up to the next
     higher power of 2 (but not to exceed 512).

   Return Values
     dma_mapalloc returns a pointer to the DMA map structure on models that
     support DMA maps.  On other models, dma_mapalloc returns -1 to indicate
     that DMA mapping is not possible on that model.

   See Also
     dma_map(D3X), dma_mapaddr(D3X), dma_mapfree(D3X), vme_adapter(D3X).