linux-kernel - Re: [PATCH 02/10] mfd: cros_ec: IRQs for cros

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Message-ID: <20140618164621.GB25353@lee--X1>
Date:	Wed, 18 Jun 2014 17:46:21 +0100
From:	Lee Jones <lee.jones@...aro.org>
To:	Doug Anderson <dianders@...omium.org>
Cc:	Andrew Bresticker <abrestic@...omium.org>,
	Stephen Warren <swarren@...dotorg.org>,
	Olof Johansson <olof@...om.net>,
	Sonny Rao <sonnyrao@...omium.org>,
	linux-samsung-soc <linux-samsung-soc@...r.kernel.org>,
	Javier Martinez Canillas <javier.martinez@...labora.co.uk>,
	Bill Richardson <wfrichar@...omium.org>,
	Simon Glass <sjg@...omium.org>,
	Wolfram Sang <wsa@...-dreams.de>,
	"broonie@...nel.org" <broonie@...nel.org>,
	Samuel Ortiz <sameo@...ux.intel.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 02/10] mfd: cros_ec: IRQs for cros_ec should be optional

On Wed, 18 Jun 2014, Doug Anderson wrote:

> Lee,
> 
> On Wed, Jun 18, 2014 at 12:55 AM, Lee Jones <lee.jones@...aro.org> wrote:
> > On Mon, 16 Jun 2014, Doug Anderson wrote:
> >
> >> From: Bill Richardson <wfrichar@...omium.org>
> >>
> >> Preparing the way for the LPC device, which is just a plaform_device without
> >> interrupts.
> >>
> >> Signed-off-by: Bill Richardson <wfrichar@...omium.org>
> >> Signed-off-by: Doug Anderson <dianders@...omium.org>
> >> ---
> >>  drivers/mfd/cros_ec.c | 26 +++++++++++++-------------
> >>  1 file changed, 13 insertions(+), 13 deletions(-)
> >>
> >> diff --git a/drivers/mfd/cros_ec.c b/drivers/mfd/cros_ec.c
> >> index 38fe9bf..bd6f936 100644
> >> --- a/drivers/mfd/cros_ec.c
> >> +++ b/drivers/mfd/cros_ec.c
> >> @@ -119,17 +119,15 @@ int cros_ec_register(struct cros_ec_device *ec_dev)
> >>                       return -ENOMEM;
> >>       }
> >>
> >> -     if (!ec_dev->irq) {
> >> -             dev_dbg(dev, "no valid IRQ: %d\n", ec_dev->irq);
> >> -             return err;
> >> -     }
> >> -
> >> -     err = request_threaded_irq(ec_dev->irq, NULL, ec_irq_thread,
> >> -                                IRQF_TRIGGER_LOW | IRQF_ONESHOT,
> >> -                                "chromeos-ec", ec_dev);
> >> -     if (err) {
> >> -             dev_err(dev, "request irq %d: error %d\n", ec_dev->irq, err);
> >> -             return err;
> >> +     if (ec_dev->irq) {
> >> +             err = request_threaded_irq(ec_dev->irq, NULL, ec_irq_thread,
> >> +                                     IRQF_TRIGGER_LOW | IRQF_ONESHOT,
> >> +                                     "chromeos-ec", ec_dev);
> >
> > Is there anything stopping you using the devm_* version?
> 
> I'm generally quite hesitant about using the devm_ IRQ functions.
> Requesting an IRQ enables the IRQ at the time of request and freeing
> it disables it, right?  Leaving it up to the the devm subsystem to
> disable your IRQ tends to be a race waiting to happen if an IRQ
> happens after you've freed all your memory / cleaned up all your
> state.
> 
> Looking at cros_ec in particular though:
> 
> * Right now the last thing done in cros_ec_remove() (which is the last
> thing in both cros_ec_i2c_remove and cros_ec_spi_remove) is to free
> the IRQ.  That means that you're right: we could switch to devm_ in
> this case and it wouldn't introduce any new bugs.
> 
> * ...but I'm not convinced that the location of the free_irq() today
> is quite right.  I couldn't actually get it to crash or hang, but
> there is a time period where we've called mfd_remove_devices() and the
> IRQ is still active.  That doesn't seem like a super great situation
> to be in.  I'll add a move of the irq_free to the patch series.

I guess if you're concerned about ordering you could always use
devm_free_irq() in the places where you think it should be freed
earlier than release.  I'm pretty sure that discludes the failure
patch in probe() though, so we'd still be able to rid a few lines.

-- 
Lee Jones
Linaro STMicroelectronics Landing Team Lead
Linaro.org │ Open source software for ARM SoCs
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