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 22:31:24 +0530
From:	Vinod Koul <vinod.koul@...el.com>
To:	Jassi Brar <jaswinder.singh@...aro.org>
Cc:	"Bounine, Alexandre" <Alexandre.Bounine@....com>,
	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, 2011-10-17 at 21:22 +0530, Jassi Brar 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.
Yes agreed, but we already decided and marked it as depreciated.

> And then either this argument would be RapidIO specific (unfair
> to other users) or generic. In latter case what would it look like ?
My initial thoughts were to add an argument which only the specific dmac
knows howto decode and is filled by its client. As i said for existing
users and people who don't require dynamic information wouldn't bother.
The pros
 - allows us to support RIO kind of subsystems where one needs to pass
subsystem specific information for programing the dmac
 - doesn't require us to add subsystem specific stuff in dmaengine,
today its RIO tomorrow some other folks may want to add. We want to
maintain dmaengine as a generic framework, while also trying to support
multiple audiences.
Cons:
 - there is no guarantee;  dmac expects foo and clients pass bar

I am okay if we have alternate way to support this with above goal :)

-- 
~Vinod

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