Re: Access to DMA memory while DMA in progress?

[Eduardo Horvath <eeh%NetBSD.org@localhost>]

On Fri, 27 Oct 2017, Mouse wrote:

> >> But I'm not sure what sort of sync calls I need to make.  [...]
> > You want to do a bus_dmamap_sync(BUS_DMASYNC_POSTREAD) [...]
> > In the NIC example above, you map the ring buffer with
> > BUS_DMA_COHERENT, fill it up and do a
> > bus_dmamap_sync(BUS_DMASYNC_PREREAD).  When you want to read it
> > (usually after getting an interrupt) you do
> > bus_dmamap_sync(BUS_DMASYNC_POSTREAD) before doing the read.
> 
> Don't you need to PREWRITE after filling it?  Based on the mental
> models I've formed, that feels necessary.

You'd want to do a PREWRITE and a POSTWRITE, but since writing wasn't part 
of your usage model I skipped that part.

Eduardo