From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <linux-kernel-owner@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
	id S1753830AbbJNN3W (ORCPT <rfc822;w@1wt.eu>);
	Wed, 14 Oct 2015 09:29:22 -0400
Received: from mail-wi0-f177.google.com ([209.85.212.177]:35727 "EHLO
	mail-wi0-f177.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
	with ESMTP id S1753698AbbJNN3U (ORCPT
	<rfc822;linux-kernel@vger.kernel.org>);
	Wed, 14 Oct 2015 09:29:20 -0400
Subject: Re: [PATCH v2 2/4] dmaengine: Add STM32 DMA driver
To: "M'boumba Cedric Madianga" <cedric.madianga@gmail.com>
References: <1444745127-1105-1-git-send-email-cedric.madianga@gmail.com>
 <1444745127-1105-3-git-send-email-cedric.madianga@gmail.com>
 <561D1689.90703@linaro.org>
 <CAOAejn1N=dFZ3nQ_hNznJQX1-fkP3r=vdYuWY4OMH65PrW3xVg@mail.gmail.com>
 <CAOAejn2pcFSn3Hf=j6zgg6Ui6GjJZrtRch6ywByHaVLsTLMk6A@mail.gmail.com>
Cc: Maxime Coquelin <mcoquelin.stm32@gmail.com>, robh+dt@kernel.org,
        pawel.moll@arm.com, Mark Rutland <mark.rutland@arm.com>,
        ijc+devicetree@hellion.org.uk, Kumar Gala <galak@codeaurora.org>,
        linux@arm.linux.org.uk, Vinod Koul <vinod.koul@intel.com>,
        linux-arm-kernel@lists.infradead.org, devicetree@vger.kernel.org,
        linux-kernel@vger.kernel.org, dmaengine@vger.kernel.org
From: Daniel Thompson <daniel.thompson@linaro.org>
Message-ID: <561E58AC.80207@linaro.org>
Date: Wed, 14 Oct 2015 14:29:16 +0100
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101
 Thunderbird/38.3.0
MIME-Version: 1.0
In-Reply-To: <CAOAejn2pcFSn3Hf=j6zgg6Ui6GjJZrtRch6ywByHaVLsTLMk6A@mail.gmail.com>
Content-Type: text/plain; charset=utf-8; format=flowed
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

On 14/10/15 14:17, M'boumba Cedric Madianga wrote:
> Hi Daniel,
>
>>>> +
>>>> +static int stm32_dma_remove(struct platform_device *pdev)
>>>> +{
>>>> +       struct stm32_dma_device *dmadev = platform_get_drvdata(pdev);
>>>> +
>>>> +       of_dma_controller_free(pdev->dev.of_node);
>>>> +
>>>> +       dma_async_device_unregister(&dmadev->ddev);
>>>> +
>>>> +       clk_disable_unprepare(dmadev->clk);
>>>
>>>
>>> What is the purpose of disabling/unpreparing the clock here?
>>> stm32_dma_alloc_chan_resources() and stm32_dma_free_chan_resources() should
>>> pair up and the clock should already be stopped.
>
> stm32_dma_remove() could be called during an on-going transfer during
> module unload.
> So in that case, it seems that disabling/unpreparing the clock is needed.

Really?

I think we need to be sure any on-going transfers are stopped.

There are multiple reasons for this, not least the risk of executing a 
callback that has been freed, but the one related to my point is that a 
single clk_disable_unprepare() will remain broken because if you don't 
know that the transfers have stopped then you don't know how many 
on-going transfers there are.


Daniel.