linux-kernel - Re: [PATCH v1 1/5] dma: Add QorIQ qDMA engine driver support

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Message-ID: <20160818091603.GT1041@n2100.armlinux.org.uk>
Date:	Thu, 18 Aug 2016 10:16:03 +0100
From:	Russell King - ARM Linux <linux@...linux.org.uk>
To:	Yuan Yao <yao.yuan@...escale.com>
Cc:	vinod.koul@...el.com, robh+dt@...nel.org, dan.j.williams@...el.com,
	mark.rutland@....com, shawnguo@...nel.org, leoyang.li@....com,
	dmaengine@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, Yuan Yao <yao.yuan@....com>
Subject: Re: [PATCH v1 1/5] dma: Add QorIQ qDMA engine driver support

On Thu, Aug 18, 2016 at 02:38:44PM +0800, Yuan Yao wrote:
> +			spin_lock(&fsl_comp->qchan->vchan.lock);
> +			if (status == DMA_COMPLETE)
> +				vchan_cookie_complete(&fsl_comp->vdesc);
> +			fsl_comp->qchan->status = status;

This is buggy - if the DMA has finished processing it, even if it
finished in error, it must _complete_ the transaction.  Completion is
not the same as being successful - it means that the DMA is no longer
processing the cookie.

The issue here is that when the _following_ transaction completes
successfully, _this_ transaction will effectively be marked as complete
due to the way the cookie system works.

So... to get this straight - "completion" means "I have finished
processing this transaction".  It does not mean "I successfully
processed this transaction without any errors."

-- 
RMK's Patch system: http://www.armlinux.org.uk/developer/patches/
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