Re: [PATCH 2/2] chipidea: Use devm_request_irq()

From: Peter Chen
Date: Wed Jul 31 2013 - 21:33:52 EST

On Wed, Jul 31, 2013 at 10:15:12AM -0400, Tejun Heo wrote:
> hello,
> On Wed, Jul 31, 2013 at 09:55:26PM +0800, Peter Chen wrote:
> > I think the main point is we should allocate managed resource which is used
> > at interrupt handler before devm_request_irq, and all resources used
> > at interrupt
> > handler should be managed.
> >
> > If we use non-managed resource at interrupt handler, but using managed interrupt
> > handler, things still will go wrong if there is an odd (unexpected)
> > interrupt after
> > we finish deactivation at removal.
> In general, applying devm partially isn't a good idea. It's very easy
> to get into trouble thanks to release order dependency which isn't
> immediately noticeable and there have been actual bugs caused by that.
> The strategies which seem to work are either
> * Convert everything over to devm by wrapping deactivation in a devres
> callback too. As long as your init sequence is sane (ie. irq
> shouldn't be request before things used by irq are ready).
> * Allocate all resources using devres but shut down the execution
> engine in the remove_one(). Again, as all releases are controlled
> by devres, you won't have to worry about messing up the release
> sequencing.

thanks, Tejun. So, Alex and Fabio, this patch may not be suitable currently,
since many resources at both EHCI and device side are non-managed.

Best Regards,
Peter Chen

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