Messages in this thread | | | Date | Wed, 8 Nov 2017 22:11:02 +0000 | From | Mark Brown <> | Subject | Re: [PATCH AUTOSEL for-4.9 04/53] spi: imx: adjust watermark level according to transfer length |
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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. [unhandled content-type:application/pgp-signature] | |