linux-kernel - Re: [PATCH 1/4 v2] dmaengine: add a tx_free method to struct dma_async_tx

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Date:	Thu, 11 Dec 2008 17:56:51 +0100 (CET)
From:	Guennadi Liakhovetski <g.liakhovetski@....de>
To:	Dan Williams <dan.j.williams@...el.com>
cc:	Guennadi Liakhovetski <g.liakhovetski@....de>,
	linux-kernel@...r.kernel.org,
	linux-fbdev-devel@...ts.sourceforge.net, adaplas@...il.com,
	Sascha Hauer <s.hauer@...gutronix.de>,
	linux-arm-kernel@...ts.arm.linux.org.uk
Subject: Re: [PATCH 1/4 v2] dmaengine: add a tx_free method to struct
 dma_async_tx_descriptor

On Thu, 11 Dec 2008, Dan Williams wrote:

> On Thu, Dec 11, 2008 at 8:55 AM, Guennadi Liakhovetski
> <g.liakhovetski@....de> wrote:
> >
> > Sorry, actually, it's not VIDIOC_DQBUF where we have to free buffer(s),
> > it's VIDIOC_STREAMOFF. And in a normal case there are no more completion
> > interrupts, no allocation requests, and noone is interested in
> > is_tx_complete. Normally you would just get a dma_release_channel after
> > that. Or, of course, the application may decide to restart capture, then
> > we get requests, completions, etc. again. So, yes, I could do this, it
> > just seems a bit unnatural to me.
> 
> Could the application tolerate another call to dma_request_channel
> when it restarts?  I.e. just call dma_release_channel from the ioctl
> to clean everything up and not worry about another free() mechanism?

For V4L - yes, I could do this. But is it a good idea to hard-code into a 
"generic" dma driver (or at least something that pretends to be a generic 
driver), that descriptors can only ever be freed by releasing the 
channel?...

Thanks
Guennadi
---
Guennadi Liakhovetski, Ph.D.
Freelance Open-Source Software Developer
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