6. PMMU support functions

These functions convert from virtual addresses (as the CPU uses them) to PCI bus addresses and back. This is necessary since the memory may be mapped non-linear by the PMMU even when not using virtual memory (it is on the MILAN).

It is required that a resource (ie. a region of memory or IO space on a PCI card) is mapped contiguously, so that a simple offset can be used when copying to/from memory on a PCI card.

These functions might be limited to TOS or TOS-like operating systems. If an operating systems uses a different memory layout, it may need to provide its own functions which drivers can use.

When using these functions, the driver does not need to care about DMA offsets at all.

6.1 Get Pagesize

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get_pagesize:
Input:
  none
Output:
  D0.L      active pagesize or 0 if paging is not active

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6.2 Convert virtual to PCI bus address

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virt_to_bus:
Input:
  D0.L      device handle
  D1.L      address in virtual CPU space
  A0.L      pointer to mem-struct for results
Output:
  D0.L      error code

If D0.L indicates no error, mem-struct is filled as follows:
mem-struct:
  DS.L 1   ;PCI bus address
  DS.L 1   ;length of contiguous mapped area, 0 if no DMA is possible 
           ;at this address

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6.3 Convert PCI bus to virtual address

This function is the reverse of virt_to_bus. It might be slow, so the driver should avoid using it if it can determine the address by other means.

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bus_to_virt:
Input:
  D0.L      device handle
  D1.L      PCI bus address
  A0.L      pointer to mem-struct for results
Output:
  D0.L      error code

If D0.L indicates no error, mem-struct is filled as follows:
mem-struct:
  DS.L 1   ;CPU (virtual) address
  DS.L 1   ;length of contiguous mapped area

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The following two functions do not depend on a special device, thus they do not get a device handle.

6.4 Convert virtual to physical CPU address

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virt_to_phys:
Input:
  D0.L      address in virtual CPU space
  A0.L      pointer to mem-struct for results
Output:
  D0.L      error code

If D0.L indicates no error, mem-struct is filled as follows:
mem-struct:
  DS.L 1   ;physical CPU address
  DS.L 1   ;length of contiguous mapped area, 0 if not mapped

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6.5 Convert physical CPU to virtual address

This function is the reverse of virt_to_bus. It might be slow, so the driver should avoid using it if it can determine the address by other means.

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phys_to_virt:
Input:
  D0.L      physical CPU address
  A0.L      pointer to mem-struct for results
Output:
  D0.L      error code

If D0.L indicates no error, mem-struct is filled as follows:
mem-struct:
  DS.L 1   ;CPU (virtual) address
  DS.L 1   ;length of contiguous mapped area

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