lkml.org 
[lkml]   [2017]   [Nov]   [8]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH AUTOSEL for-4.9 04/53] spi: imx: adjust watermark level according to transfer length
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]
\
 
 \ /
  Last update: 2017-11-08 23:11    [W:0.076 / U:2.852 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site