linux-kernel - Re: [PATCH v2 2/4] dmaengine: Add STM32 DMA driver

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Date:	Thu, 15 Oct 2015 09:37:08 +0530
From:	Vinod Koul <vinod.koul@...el.com>
To:	M'boumba Cedric Madianga <cedric.madianga@...il.com>
Cc:	Daniel Thompson <daniel.thompson@...aro.org>,
	Maxime Coquelin <mcoquelin.stm32@...il.com>,
	robh+dt@...nel.org, pawel.moll@....com,
	Mark Rutland <mark.rutland@....com>,
	ijc+devicetree@...lion.org.uk, Kumar Gala <galak@...eaurora.org>,
	linux@....linux.org.uk, linux-arm-kernel@...ts.infradead.org,
	devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
	dmaengine@...r.kernel.org
Subject: Re: [PATCH v2 2/4] dmaengine: Add STM32 DMA driver

On Wed, Oct 14, 2015 at 05:41:26PM +0200, M'boumba Cedric Madianga wrote:
> 2015-10-14 17:28 GMT+02:00 Daniel Thompson <daniel.thompson@...aro.org>:
> > On 14/10/15 16:26, M'boumba Cedric Madianga wrote:
> >>
> >> 2015-10-14 16:24 GMT+02:00 Daniel Thompson <daniel.thompson@...aro.org>:
> >>>
> >>>
> >>> Hmnnn...
> >>>
> >>> The dmaengine framework will WARN_ONCE() if an dmaengine is removed
> >>> whilst
> >>> it is active and also works hard to ensure dmaengine modules are not
> >>> removed
> >>> whilst there are active drivers using the framework.
> >>>
> >>> How do we get into this function whilst there is still an active DMA
> >>> channels?
> >>
> >>
> >> For example, when a user try "rmmod stm32-dma" in uart console.
> >> It will enter in stm32_dma_remove while there is potentially still active
> >> DMA.
> >
> >
> > Check dmaengine.c for yourself but I think in this case the dmaengine
> > framework will hold references to the module and prevent the remove from
> > taking place.
> 
> Yes I did it.
> As far I understand, the dmaengine framework will print a warning
> message but doesn't stop removing operation if there are some active
> clients.

we hold a ref, so removal wont work, see dma_chan_get()

-- 
~Vinod
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