On Wed, Nov 08, 2017 at 09:39:11PM +0000, Levin, Alexander (Sasha Levin) wrote: > >On Wed, Nov 08, 2017 at 08:49:55PM +0000, Levin, Alexander (Sasha Levin) > >wrote: > >This seems like an optimization not a bug fix...
> Hm, is it? I read it as "DMA is not being used at all even though we > thought we're using it". Yes, that's how I read it too. > Yes, the impact is "just" performance, but doesn't it result in quite > a significat impact? Only about double according to the initial commit adding DMA support which is frankly a bit disappointing although yeah, it's a big win. My worry is that if there's a problem with DMA on some device for which a fix wasn't backported (or where we're using a fallback) this could expose problems if we start using it. If you look at the history of the driver there's some quirks were added later on for example, and I didn't check the DMA controller drivers or anything and obviously can't see any out of tree code users may have. *Probably* it doesn't break anything but since it's not fixing anything and the risk is data corruption I'd be much more comfortable with a more thorough risk analysis.
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