Re: (reposting) how to get DMA'able memory within 4GB on 64-bit m

[Alan Cox]

> > So add another seven or eight years to your estimate
> 
> Given a little more context, I thought we were talking specifically
> about 64bit-PCI-on-32bit-machines?
> 
> Assuming that, AFAICS Ben's statement seems more correct.
> 
> And IMHO we definitely should not optimize for 64-bit-on-32-bit case. 
> Let CONFIG_HIGHMEM grow dma_addr_t to 64-bits, for that case only...

I see no good way to optimise for 64bit dma on a 32bit box. The existing API
is extremely clean, easy to understand and I don't agree with Dave's desire
to write another whole concoction.

We do need pci_set_dma_mask_bits(), which in itself lets drivers indicate
SAC/DAC capable. We do want a way for nosey or fine tuned drivers to query
SAC/DAC properties, but most drivers should be letting arch code make arch
policy. 

Alan