linux-kernel - Re: [PATCH 10/18] spi: s3c64xx: Do not require legacy DMA API in case of S3C64XX

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Date:	Tue, 13 Aug 2013 22:20:19 +0200
From:	Tomasz Figa <tomasz.figa@...il.com>
To:	Mark Brown <broonie@...nel.org>
Cc:	linux-samsung-soc@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, alsa-devel@...a-project.org,
	linux-kernel@...r.kernel.org, linux-spi@...r.kernel.org,
	Dan Williams <djbw@...com>, Jaroslav Kysela <perex@...ex.cz>,
	Kukjin Kim <kgene.kim@...sung.com>,
	Liam Girdwood <lgirdwood@...il.com>,
	Linus Walleij <linus.walleij@...aro.org>,
	Mike Turquette <mturquette@...aro.org>,
	Padmavathi Venna <padma.v@...sung.com>,
	Russell King <linux@....linux.org.uk>,
	Sangbeom Kim <sbkim73@...sung.com>,
	Takashi Iwai <tiwai@...e.de>, Vinod Koul <vinod.koul@...el.com>
Subject: Re: [PATCH 10/18] spi: s3c64xx: Do not require legacy DMA API in case of S3C64XX

On Tuesday 13 of August 2013 21:18:16 Mark Brown wrote:
> On Tue, Aug 13, 2013 at 07:55:47PM +0100, Mark Brown wrote:
> > I'm still debugging what's going on here - the basic refcounting all
> > looks OK in the SPI driver, I can see it requesting and releasing with
> > the refcounts all going back to zero in the DMA driver as expected but
> > when we come back to the device later on dmaengine is deciding the
> > device is unavailable quite early on in the process.
> 
> The failure is happening because this check is failing:
> 
> 	/* devices with multiple channels need special handling as we need 
to
> 	 * ensure that all channels are either private or public.
> 	 */
> 	if (dev->chancnt > 1 && !dma_has_cap(DMA_PRIVATE, dev->cap_mask))
> 		list_for_each_entry(chan, &dev->channels, device_node) {
> 			/* some channels are already publicly allocated */
> 			if (chan->client_count) {
> 
> which is happening because dma1chan0 (which is on the same DMA
> controller as the SPI controller) and in fact every other DMA channel
> had references grabbed by the network stack dmaengine helpers which I'd
> enabled in config.  The fact that they do that is unhelpful, it renders
> the API mostly useless, but is nothing to do with this series.
> 
> Having tweaked the config everything appears to work so:
> 
> Tested-by: Mark Brown <broonie@...aro.org>
> 
> though the whole thing with the filter function is as I say a bit fun
> from a code review point of view.

I believe you just found another brokenness of current DMA channel 
matching.

Thanks for testing.

Best regards,
Tomasz

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