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

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Message-ID: <20130731094434.GC1754@pengutronix.de>
Date:	Wed, 31 Jul 2013 11:44:34 +0200
From:	Uwe Kleine-König 
	<u.kleine-koenig@...gutronix.de>
To:	Mark Brown <broonie@...nel.org>
Cc:	Peter Chen <peter.chen@...escale.com>,
	Fabio Estevam <festevam@...il.com>,
	alexander.shishkin@...ux.intel.com, kernel@...gutronix.de,
	linux-usb@...r.kernel.org,
	Fabio Estevam <fabio.estevam@...escale.com>,
	Tejun Heo <htejun@...il.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()

[Expanded Cc: a bit]

Hello,

On Wed, Jul 31, 2013 at 10:05:12AM +0100, Mark Brown wrote:
> On Wed, Jul 31, 2013 at 10:46:45AM +0200, Uwe Kleine-König wrote:
We're discussing about devm_request_irq and wonder what happens at
remove time when the irq is still active.

> > OK, so the possible problem is that remove is called while the irq is
> > still active. That means you have to assert that all resources the irq
> > handler is using (e.g. ioremap, clk_prepare_enable) are only freed
> > *after* the irq is done. For ioremap that means it must be done using
> > devm_ioremap_resource. For a clock it's not that easy because the irq
> > handler has to assert that a used clk is kept prepared which can only be
> > done using clk_prepare which in turn is not allowed in an irq handler.
> 
> > Hmm. So the only possible fixes are
> > 	- devm* can be told to also care about clk_disable_unprepare
> > 	- after disabling irqs in the remove callback wait for all
> > 	  active irqs to be done. (i.e. call synchronize_irq(irq))
> > 	- don't use devm_request_irq
> 
> I'm not sure that devm_ guarantees any ordering in the cleanups it does
> so I'd not like to rely on the first option either, if there were some
> guarantee of that it'd help.  The nice thing about explicitly freeing
> the IRQ is that you can tell that all this stuff is safe by inspection.
devm_* at least uses list_for_each_entry_reverse
(drivers/base/devres.c:release_nodes()). Without this guarantee devm_
would not make much sense IMHO.

To also manage clks, we'd need something like:

	devm_clk_prepare(&dev, some_clk);

that makes devm_clk_release also call clk_unprepare the right number of
times. Maybe also the same for devm_clk_enable? Does this make sense?

Best regards
Uwe

-- 
Pengutronix e.K.                           | Uwe Kleine-König            |
Industrial Linux Solutions                 | http://www.pengutronix.de/  |
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