linux-kernel - Re: question about drivers/dma/dma-jz4780.c

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Message-ID: <20150723172110.GB29916@localhost>
Date:	Thu, 23 Jul 2015 22:51:10 +0530
From:	Vinod Koul <vinod.koul@...el.com>
To:	Alex Smith <alex.smith@...tec.com>
Cc:	Julia Lawall <julia.lawall@...6.fr>, Zubair.Kakakhel@...tec.com,
	dmaengine@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: question about drivers/dma/dma-jz4780.c

On Wed, Jul 22, 2015 at 03:26:01PM +0100, Alex Smith wrote:

> >>>I think the explicit devm_free_irq() here is unnecessary, as when remove is
> >>>called there should be no remaining users of the DMA controller and therefore
> >>>no chance of an IRQ occurring between the controller being unregistered and an
> >>>implicit IRQ release afterwards.
> >Are you ensuring that device can no longer sent interrupts and all instances
> >of tasklet running or either completed are terminated and no further tasklet
> >can be spawned?
> 
> Hi Vinod,
> 
> If I understand correctly, when remove() is called, there should be
> no more users of the DMA controller, enforced by the module
> reference count.
> 
> Wouldn't that guarantee that there are no more transactions running
> and therefore no chance of an interrupt from the controller or a
> tasklet still running?

That will only guarantee no new requests are recieved, but you may have
tasklet already scheduled or irq sent from HW how do you prevent that?

-- 
~Vinod

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