Re: [PATCH V2 6/6] spi/spi-pl022: Request/free DMA channels as and when required.

[Russell King - ARM Linux <linux-lFZ/pmaqli7XmaaqVzeoHQ@public.gmane.org>]

On Wed, Aug 10, 2011 at 03:39:28PM +0530, Jassi Brar wrote:
> On Wed, Aug 10, 2011 at 2:59 PM, viresh kumar <viresh.kumar-qxv4g6HH51o@public.gmane.org> wrote:
> > On 08/10/2011 02:30 PM, Russell King - ARM Linux wrote:
> >>> > They must be allocated when they are required and must be freed after we are
> >>> > done with transfers. So that they can be used by other users.
> >> Which DMA engine driver requires this?
> >>
> >
> > dw_dmac.c
> >
> >> Normally, when we have DMA engine drivers with multiple request signals,
> >> the slave peripheral side publishes several virtual channels which are
> >> claimed by the peripheral drivers.  This (amongst other things) allows
> >> the peripheral drivers to hold claim to one of the virtual channels
> >> all the time that it's required.
> >
> > If users of DMA expect DMA engine drivers to work this way, then we should
> > have this mentioned clearly in DMA slave documentation.
> 
> The requirement stems from the fact that most DMACs(esp third party) could be
> made to reroute req-signals by the platform, it has not much to do with the API.
> IMO, all dmac drivers should be implemented that way to be on the safer side.

No it isn't.  It's to do with how the physical channels are used.

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