linux-kernel - Re: [PATCH 5/7 v2] dma: sh: use an integer slave ID to improve API compatibility

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Date:	Mon, 16 Jul 2012 12:23:07 +0530
From:	Vinod Koul <vinod.koul@...ux.intel.com>
To:	Guennadi Liakhovetski <g.liakhovetski@....de>
Cc:	Magnus Damm <magnus.damm@...il.com>, linux-sh@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 5/7 v2] dma: sh: use an integer slave ID to improve API
 compatibility

On Mon, 2012-07-16 at 08:37 +0200, Guennadi Liakhovetski wrote:
> On Mon, 16 Jul 2012, Vinod Koul wrote:
> 
> > On Thu, 2012-07-05 at 12:29 +0200, Guennadi Liakhovetski wrote:
> > > diff --git a/include/linux/sh_dma.h b/include/linux/sh_dma.h
> > > index a79f10a..4e83f3e 100644
> > > --- a/include/linux/sh_dma.h
> > > +++ b/include/linux/sh_dma.h
> > > @@ -27,10 +27,10 @@ struct sh_dmae_slave {
> > >   * a certain peripheral
> > >   */
> > >  struct sh_dmae_slave_config {
> > > -       unsigned int                    slave_id;
> > > -       dma_addr_t                      addr;
> > > -       u32                             chcr;
> > > -       char                            mid_rid;
> > > +       int             slave_id;
> > > +       dma_addr_t      addr;
> > > +       u32             chcr;
> > > +       char            mid_rid;
> > >  }; 
> > why would you want to keep your own slave_id and addr fields when they
> > are already provided in struct dma_slave_config.
> 
> Modifying the driver's API would break all its clients.
rightly so, they need to be moved too.

> 
> > Also while at it, what
> > would be the use of last tow fields, what do they describe?
> 
> They tell the driver how the channel has to be configured to support this 
> specific client. They are values of two specific registers. In fact, CHCR 
> means exactly that - CHannel Control Register.
what exactly does the channel control register do in shdma? Should shdma
driver deduce this value rather than client giving it?
Same question for mid_rid?


-- 
~Vinod

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