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

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Message-ID: <Pine.LNX.4.64.1207160832540.12302@axis700.grange>
Date:	Mon, 16 Jul 2012 08:37:28 +0200 (CEST)
From:	Guennadi Liakhovetski <g.liakhovetski@....de>
To:	Vinod Koul <vinod.koul@...ux.intel.com>
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, 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.

> 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.

> Would it be possible to get rid of this structure completely? At least
> first two fields should go away.

Migration has to be performed gradually. If this approach and patches are 
accepted, then all client drivers can be migrated, then thr legacy API can 
be dropped.

Thanks
Guennadi
---
Guennadi Liakhovetski, Ph.D.
Freelance Open-Source Software Developer
http://www.open-technology.de/
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