Re: [PATCH 01/16] Blackfin SPI Driver: ensure cache coherency before doing DMA

David Brownell
2008-11-20T22:05:23Z

On Thursday 20 November 2008, Mike Frysinger wrote:
> On Thu, Nov 20, 2008 at 16:47, David Brownell wrote:

> > Basically, dma_map_single(), dma_unmap_single() ... and
> > remember that the caller may have done the mappings for
> > you already.
>
> these arent required to provide coherent memory right ? if that's the
> case, i can take a look at getting things updated.

Right. If caller provides dma-coherent memory to you, they
must also have provided the DMA addresses the controller
driver should be using ... so you won't need dma mapping
calls on those paths.

> > It'd be nice if one of patches snuck in a comment on that
> > point: "Full duplex only works for non-DMA transfers."
> > Same rationale: you may know this hardware inside out,
> > but the next person won't.
>
> well, hopefully if they dont know they wont be touching the driver ;).
> i'll add a comment in this code chunk. thanks for the feedback.

The way it usually works is someone observes a problem and
then starts experimenting on relevant code. So they learn
a bit while debugging ... and code authors/maintainers need
to keep that learning curve from being too steep. ;)

- Dave