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

[Daniel Thompson]

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.
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