Subject: Re: [patch 9/9] powerpc/cell: Add DMA_ATTR_STRONG_ORDERING dma attribute and use in IOMMU code

From: Roland Dreier <[email-masked]>
Date: Tue, 15 Jul 2008 19:18:46 -0700

> This is all about inbound transfers, i.e. DMAs coming from the I/O bridge
 > into the CPU, both DMA read and DMA write.

OK -- at a minimum I think the documentation should make that clear.  As
it stands the description of what this does is pretty much impossible to
parse and understand.

 > Strong ordering is only active when both the bridge and the IOMMU enable
 > it, but for correctly written drivers, this only results in a slowdown.

So when would someone use this dma attribute?  As a hack to fix drivers
where the real fix is too complicated?

 - R.