linux-kernel - RE: [RFC PATCH 0/2] dmaengine: at_hdmac: fix locking according to slave DMA requirements

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Date:	Fri, 31 Jan 2014 10:56:25 +0000
From:	Jouko Haapaluoma <jouko.haapaluoma@...ice.com>
To:	Nicolas Ferre <nicolas.ferre@...el.com>
CC:	Sami Pietikäinen <Sami.Pietikainen@...ice.com>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"dmaengine@...r.kernel.org" <dmaengine@...r.kernel.org>,
	"vinod.koul@...el.com" <vinod.koul@...el.com>
Subject: RE: [RFC PATCH 0/2] dmaengine: at_hdmac: fix locking according to
 slave DMA requirements

Hi

Thanks for the patches. We got the DMA working for now but the tasklet_disable() and tasklet_enable() had to be removed from atc_control().

If the device driver calls dmaengine_terminate_all() from the callback (like in our previous deadlock example), the tasklet_disable() will cause
another deadlock because the tasklet will then wait for itself to close.

The tasklet_disable() seems to be used to ensure that no tasklet is running when terminating the DMA transfers. This prevents the terminate_all from
happening in between the critical sections in the tasklet which are locked with atchan->lock. Maybe the tasklet needs to be implemented so that it can
detect and recover if the terminate_all was called in between the critical sections in the tasklet?

BR,
Jouko Haapaluoma
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