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

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Date:	Tue, 7 Feb 2012 06:01:23 -0800
From:	"Bounine, Alexandre" <Alexandre.Bounine@....com>
To:	Vinod Koul <vinod.koul@...el.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, Feb 06, 2012 at 10:40 PM, Vinod Koul wrote:
> 
> 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?
> 
Currently function private_candidate() allows filtering function
not to be specified and therefore skip the filter check.
It may be a good safety measure to ensure that channels specified
as DMA_SLAVE_EXT provide a corresponding filter routine so they
positively identify dma channel that will accept intended extra parameter.
I assume that a system may have more than one dmac registered as DMA_SLAVE_EXT. 

This is what I have for RapidIO - the filter call ensures that DMA
channel is associated with a RapidIO controller that provides access
to the specified SRIO device.


Alex.