linux-kernel - RE: [RFC PATCH 1/2] RapidIO: Add DMA Engine support for RIO data transfers

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Date:	Mon, 17 Oct 2011 11:16:14 -0700
From:	"Bounine, Alexandre" <Alexandre.Bounine@....com>
To:	Jassi Brar <jaswinder.singh@...aro.org>,
	Vinod Koul <vinod.koul@...el.com>
CC:	Dan <dan.j.williams@...el.com>, <akpm@...ux-foundation.org>,
	<linux-kernel@...r.kernel.org>, <linuxppc-dev@...ts.ozlabs.org>,
	Kumar Gala <galak@...nel.crashing.org>,
	Matt Porter <mporter@...nel.crashing.org>,
	Li Yang <leoli@...escale.com>
Subject: RE: [RFC PATCH 1/2] RapidIO: Add DMA Engine support for RIO data transfers

On Mon, Oct 17, 2011 at 11:53 AM, Jassi Brar
<jaswinder.singh@...aro.org> wrote:
> 
> On 15 October 2011 23:05, Vinod Koul <vinod.koul@...el.com> wrote:
> 
> > Another alternate approach could be to add one more argument to
> > prep_slave_sg API which allows us to pass additional runtime
specific
> > parameters. This can be NULL and unused for existing drivers and
used
> in
> > RIO and any future subsystems which want to use dmaengine.
> > Thoughts...?
> >
> That doesn't sound much different than passing the data via
> dma_chan.private during prep_slave_sg. Only now we add to
> the number of arguments.
One dma_chan may be used by multiple drivers requesting data transfer.
In this case we will need a lock to keep dma_chan and its private
coupled together. 
If we consider this coupling as a valid way we may think about
adding a lock member into dma_chan structure. This will make locking
more effective for configurations with multiple DMA channels. 

> And then either this argument would be RapidIO specific (unfair
> to other users) or generic. In latter case what would it look like ?
It should not be RapidIO specific. Just transfer specific context that
will be interpreted by participants. Given that we have a channel
filtering mechanism there is a little chance of wrongful usage of
that parameter.

Alex.
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