linux-kernel - Re: [PATCH 3/4] fsldma: remove DMA

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Message-ID: <20100929221931.GE20748@ovro.caltech.edu>
Date:	Wed, 29 Sep 2010 15:19:31 -0700
From:	"Ira W. Snyder" <iws@...o.caltech.edu>
To:	Dan Williams <dan.j.williams@...el.com>
Cc:	linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org
Subject: Re: [PATCH 3/4] fsldma: remove DMA_SLAVE support

On Wed, Sep 29, 2010 at 02:52:16PM -0700, Dan Williams wrote:
> On Mon, Sep 27, 2010 at 3:57 PM, Ira W. Snyder <iws@...o.caltech.edu> wrote:
> > Now that the generic DMAEngine API has support for scatterlist to
> > scatterlist copying, this implementation of the DMA_SLAVE API is no
> > longer necessary.
> >
> > In order to let device_control() continue to function, a stub
> > device_prep_slave_sg() function is provided. This allows custom device
> > configuration, such as enabling external control.
> >
> 
> > +       case DMA_SLAVE_CONFIG:
> > +
> > +               cfg = (struct fsldma_slave_config *)arg;
> 
> Now that I actually see someone trying to use the recommended
> extension model it comes across as unsafe, what guarantees that arg is
> pointing to a fsldma_slave_config.  At at minimum you could ensure
> that this channel has been claimed for private usage which loosely
> implies that the client knows that it is talking to an fsldma channel.
>  Even safer is to just assign you a one-off dma_ctrl_cmd
> (FSLDMA_EXTERNAL_START) for this purpose.  Otherwise this and the
> other patches look good.
> 

I agree, it is a very unsafe model.

I'll take your suggestion, and do that instead. A new patch will be
forthcoming shortly.

Thanks,
Ira
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