PCIe Access - achieve bursts without DMA

[Michael Moese]

On Mon, Feb 03, 2014 at 10:17:43AM +0000, David Laight wrote:

> We achieved about twice that using the PEX dma controller.

> Your 3MB/s for single word transfers is similar to what we saw.
> Cycle times that make an ISA bus look fast.

Indeed, this is a really poor performance. I know we could achieve much
more performance using DMA, we have several products where we simply 
don't have DMA available - this requires searching for other paths.

My ioremap_wt() could help in these situations, at least increasing
performance for non-DMA operation to a not-that-bad level.

I don't know if other devices could benefit from this, but surely we
got several IPs that would, but those were not yet upstreamed, we're
still working on this.

Michael