lkml.org 
[lkml]   [2012]   [Mar]   [8]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
SubjectRe: [PATCH/RFC] dmaengine: add a slave parameter to __dma_request_channel()
From
Date
On Thu, 2012-03-08 at 12:22 +0100, Guennadi Liakhovetski wrote:
> On Thu, 8 Mar 2012, Vinod Koul wrote:
>
> > On Thu, 2012-03-08 at 11:16 +0100, Guennadi Liakhovetski wrote:
> > > I still have the impression, that my specific use-case (sh-mobile), where
> > > channels can be freely configured for use by _ANY_ client on one of
> > > _SEVERAL_ DMAC instances, is not fully understood or taken into account.
> > > For this driver any kind of fixed mapping means, that we'd have to use
> > > both virtual channels and controllers, adding _a lot_ of complexity to the
> > > DMAC driver and making the dmaengine core just an "obfuscation layer."
> > > Yes, I remember Russell proposing core helpers for this. They would help,
> > > but (1) when would they be available, (2) how well would they be suitable
> > > for us, (3) they'd take the coding / maintainance burden away, but
> > > wouldn't reduce complexity and run-time overhead.
> > Lets try to address you case as well.
> > On a typical platform
>
> Let's take the mackerel board with the sh7372 SoC. it's not the state of
> the art, but that's what I'm currently working with and it should give us
> a good enough idea
>
> > 1) how many dma controllers you have?
>
> currently supported 5 of 3 types (3 of type A, 1 of each of the types B
> and C), all handled by the same driver
>
> > 2) how many clients you have
>
> huh... many. Maybe like 20 or more, and more, that are not yet supported,
> using type A, and 1 for each of types B and C
>
> > 3) which client can use what controller channel? How is mapping decided,
> > do you have a mux, is it hard wired by soc designers,....?
>
> In general - with all the current sh-mobile hardware, that I'm aware of -
> there can be several controller instances on an SoC of each controller
> type. Inside each type all instances and all channels are freely
> configurable. So, of 20 Type A clients they can use any channels on any
> one of the 3 type A controllers. Types B and C are "degenerate" cases,
> there clients are practically hard-wired to a specific DMA controller.
>
> So, we don't have to decide on mappings for type A. We just pick up any
> free channels on any controller and configure them accordingly. Whether
> there's a mux somewhere - you can say so, but it's all inside the SoC, and
> it's configured automatically ones you configure a physical channel to
> serve a specific client.
>
> > Can you pls give a description so that we ensure all models fit in the
> > final solution?
>
> That's what I've been trying to do since several days now... I've been
> saying "multiple controllers with multiple channels all freely
> configurable for any device from a list" again and again... Seems I'm
> speaking some strange language, that noone understands.
Okay. One more question before I can tell you how it can work for you
without you sweating it out :-)

So you have:
case A: Here you have N dmacs and M controllers, any controller can use
any channel, No constraints on channel assignments, right?
case B: Some hardwired controllers P which can only be used by a set
clients Q?

Anything else I missed in your description?





\
 
 \ /
  Last update: 2012-03-08 12:31    [from the cache]
©2003-2011 Jasper Spaans