iommu hypervisor hypothetical

[John Rose]

> So just change the prototype of tce_build
> to return success/failure, and handle it accordingly in iommu_alloc
> (DMA_ERROR_CODE). The error should move on up the stack from there.

I'm thinking of functions like dma_map_single(), which returns the
unsigned type dma_addr_t.  Suppose H_HCE_PUT fails, and this gets
propagated up to the device driver through DMA_ERROR_CODE.  The PAPR
currently defines 2 ways in which this could fail, and we're considering
at least one more.  One error code doesn't seem sufficient.

> Or did I misunderstand your question in the first place? It's sort of
> sparse on details. :-)

You know how it goes :)  I guess my question is whether passing specific
failure conditions up the call chain is permissible/feasible, and
whether the prototypes for the various device driver DMA utilities are
set in stone.

Thanks-
John