linux-kernel - RE: [PATCH 01/11] dmaengine: add context parameter toprep_slave_sgand prep_dma

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Date:	Tue, 07 Feb 2012 09:09:53 +0530
From:	Vinod Koul <vinod.koul@...el.com>
To:	"Bounine, Alexandre" <Alexandre.Bounine@....com>
Cc:	Russell King <rmk@....linux.org.uk>, dan.j.williams@...el.com,
	linux-kernel@...r.kernel.org, akpm@...ux-foundation.org,
	Jassi Brar <jaswinder.singh@...aro.org>,
	Kumar Gala <galak@...nel.crashing.org>,
	Matt Porter <mporter@...nel.crashing.org>,
	Li Yang <leoli@...escale.com>
Subject: RE: [PATCH 01/11] dmaengine: add context parameter
 toprep_slave_sgand prep_dma_cyclic

On Mon, 2012-02-06 at 10:45 -0800, Bounine, Alexandre wrote:
> On Mon, Feb 06, 2012 at 1:07 PM, Vinod Koul wrote:
> > 
> > On Mon, 2012-02-06 at 09:02 -0800, Bounine, Alexandre wrote:
> > >
> > > What if we introduce another dma_transaction_type like DMA_SLAVE_EXT
> > > (extended?).
> > > In this case all devices that adhere to the generic SLAVE interface
> > > still be
> > > registered as DMA_SLAVE and those that do not follow generic route
> > use
> > > DMA_SLAVE_EXT.
> > that way it would be channel specific not transaction specific as you
> > had asked for...?
> > 
> > Again, how does this solve problem of passing parameters while
> > preventing abuse...
> 
> This gives a channel-specific treatment to the parameter. Channels registered
> as DMA_SLAVE never expect an extra parameter (BUG_ON if the pointer is not NULL).
> In the generic use scenario described by Russell clients are safe to request
> any such channel without an additional HW knowledge (as it is now).
> 
> Channels registered as DMA_SLAVE_EXT will accept a pointer to parameter structure.
> This, combined with configuration specific wrappers as you described
> in earlier e-mail with #ifdef CONFIG_RAPIDIO, should ensure that there is no
> unexpected treatment of (void *) parameter. Also for channels registered
> as DMA_SLAVE_EXT a corresponding filter routine must be provided. 
Okay this sounds better :)
Sorry I didnt quite get the last line about filter routine?

-- 
~Vinod

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