linux-kernel - Re: [PATCHv8] dmaengine: Add support for BCM2835

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Date:	Tue, 3 Dec 2013 12:12:22 +0000
From:	Russell King - ARM Linux <linux@....linux.org.uk>
To:	Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc:	Florian Meier <florian.meier@...lo.de>,
	Stephen Warren <swarren@...dotorg.org>,
	Vinod Koul <vinod.koul@...el.com>,
	Dan Williams <dan.j.williams@...el.com>,
	devicetree <devicetree@...r.kernel.org>,
	"alsa-devel@...a-project.org" <alsa-devel@...a-project.org>,
	Mark Brown <broonie@...nel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	linux-rpi-kernel <linux-rpi-kernel@...ts.infradead.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	dmaengine <dmaengine@...r.kernel.org>
Subject: Re: [PATCHv8] dmaengine: Add support for BCM2835

On Tue, Dec 03, 2013 at 02:04:18PM +0200, Andy Shevchenko wrote:
> On Mon, 2013-12-02 at 20:12 +0100, Florian Meier wrote:
> > +static void bcm2835_dma_free(struct bcm2835_dmadev *od)
> > +{
> > +	while (!list_empty(&od->ddev.channels)) {
> > +		struct bcm2835_chan *c = list_first_entry(&od->ddev.channels,
> > +			struct bcm2835_chan, vc.chan.device_node);
> > +
> 
> list_for_each_entry_safe() suits well here.
> 
> > +		list_del(&c->vc.chan.device_node);
> > +		tasklet_kill(&c->vc.task);
> > +	}

For such a loop, where we're deleting all entries in a list,
list_for_each_entry_safe() is a little heavier than necessary.  This
is how the code would look:

static void bcm2835_dma_free(struct bcm2835_dmadev *od)
{
	struct bcm2835_chan *c, *next;

	list_for_each_entry_safe(c, next, &od->ddev.channels,
				 vc.chan.device_node) {
		list_del(&c->vc.chan.device_node);
		tasklet_kill(&c->vc.task);
	}

I see very little gain in this approach.
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