RFC: Removal of pci_dma_* functions

RFC: Removal of pci_dma_* functions

[Ralf Baechle]

A grep for

  pci_dac_dma_supported()
  pci_dac_page_to_dma()
  pci_dac_dma_to_page()
  pci_dac_dma_to_offset()
  pci_dac_dma_sync_single_for_cpu()
  pci_dac_dma_sync_single_for_device()

reveals that only a some platforms implement these functions and there seems
to be no single user.  Any objections against removing?  Or why did we ever
add them anyay ...

  Ralf

Re: RFC: Removal of pci_dma_* functions

[David Miller]

From: Ralf Baechle <ralf@linux-mips.org>
Date: Fri, 24 Nov 2006 17:03:59 +0000

> A grep for
> 
>   pci_dac_dma_supported()
>   pci_dac_page_to_dma()
>   pci_dac_dma_to_page()
>   pci_dac_dma_to_offset()
>   pci_dac_dma_sync_single_for_cpu()
>   pci_dac_dma_sync_single_for_device()
> 
> reveals that only a some platforms implement these functions and there seems
> to be no single user.  Any objections against removing?  Or why did we ever
> add them anyay ...

They were meant for things like those Dolphin clustering cards that
can map arbitrary amounts of remote memory on the local system.

Unfortunately, none of the drivers for these things are upstream, but
I can nearly guarentee you that those drivers use these interfaces
because they map so much memory that they cannot tolerate the
limitations imposed by IOMMUs, even the ones with 2GB mapping windows
like on sparc64.