On Sun, Jul 10, 2011 at 09:29:49AM -0500, Rob Herring wrote:

asm/dma-mapping.h only includes asm/memory.h. We are getting lucky that
linux/dma-mapping.h is picking up ARCH_HAS_DMA_SET_COHERENT_MASK because
the include path looks like this for ixp4xx and pxa: linux/dma-mapping.h
-> linux/scatterlist.h -> asm/io.h -> mach/io.h -> mach/hardware.h.

That's probably because of the way the code has changed over the last
year:

6fee48c dma-mapping: arm: use generic pci_set_dma_mask and pci_set_consistent_dma_mask

Removes HAVE_ARCH_PCI_SET_DMA_MASK from IXP4xx mach/hardware.h, thus
breaking IXP4xx machines.

5f3cd1e dma-mapping: pci: move pci_set_dma_mask and pci_set_consistent_dma_mask to pci-dma-compat.h

Removes HAVE_ARCH_PCI_SET_DMA_MASK support from drivers/pci/pci.c,
which includes linux/pci.h -> asm/pci.h -> mach/hardware.h and thus
the definition.

710224fa arm: fix "arm: fix pci_set_consistent_dma_mask for dmabounce devices"

Creates the current ARCH_HAS_DMA_SET_COHERENT_MASK stuff, placing it
into ixp4xx's and PXA's mach/hardware.h to fix the regression caused
by 6fee48c and 5f3cd1e.

So this really could do with being made more robust first, because
as you point out, the current solution is extremely fragile.