linux-kernel - Re: [PATCH 2/2] chipidea: Use devm_request

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Message-ID: <20130801013311.GH8540@nchen-desktop>
Date:	Thu, 1 Aug 2013 09:33:12 +0800
From:	Peter Chen <peter.chen@...escale.com>
To:	Alexander Shishkin <alexander.shishkin@...ux.intel.com>
CC:	Peter Chen <hzpeterchen@...il.com>,
	Mark Brown <broonie@...nel.org>,
	Uwe Kleine-König 
	<u.kleine-koenig@...gutronix.de>,
	Fabio Estevam <festevam@...il.com>,
	Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
	<kernel@...gutronix.de>, Tejun Heo <htejun@...il.com>,
	"linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
	Fabio Estevam <fabio.estevam@...escale.com>,
	Jeff Garzik <jeff@...zik.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	<linux-kernel@...r.kernel.org>,
	Mike Turquette <mturquette@...aro.org>,
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH 2/2] chipidea: Use devm_request_irq()

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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