linux-kernel - Re: [PATCH] i2c: mv64xxx: Fix compilation breakage

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Date:	Sat, 22 Mar 2014 12:11:24 +0100
From:	Arnd Bergmann <arnd@...db.de>
To:	linux-arm-kernel@...ts.infradead.org
Cc:	Maxime Ripard <maxime.ripard@...e-electrons.com>,
	Paul Gortmaker <paul.gortmaker@...driver.com>,
	Russell King - ARM Linux <linux@....linux.org.uk>,
	Wolfram Sang <wsa@...-dreams.de>,
	LKML <linux-kernel@...r.kernel.org>,
	zhuzhenhua@...winnertech.com,
	"linux-next@...r.kernel.org" <linux-next@...r.kernel.org>,
	kevin.z.m.zh@...il.com, sunny@...winnertech.com,
	shuge@...winnertech.com, linux-i2c@...r.kernel.org
Subject: Re: [PATCH] i2c: mv64xxx: Fix compilation breakage

On Friday 21 March 2014 20:17:39 Maxime Ripard wrote:
> On Fri, Mar 21, 2014 at 11:49:59AM -0400, Paul Gortmaker wrote:
> > On Mon, Mar 10, 2014 at 7:29 AM, Russell King - ARM Linux
> > <linux@....linux.org.uk> wrote:
> > > On Mon, Mar 10, 2014 at 11:58:08AM +0100, Maxime Ripard wrote:
> > >> On Fri, Mar 07, 2014 at 04:08:36PM +0000, Russell King - ARM Linux wrote:
> > >> > On Fri, Mar 07, 2014 at 03:59:30PM +0100, Maxime Ripard wrote:
> > >> > > @@ -900,7 +902,8 @@ mv64xxx_i2c_probe(struct platform_device *pd)
> > >> > >  exit_free_irq:
> > >> > >   free_irq(drv_data->irq, drv_data);
> > >> > >  exit_reset:
> > >> > > - if (pd->dev.of_node && !IS_ERR(drv_data->rstc))
> > >> > > + if (pd->dev.of_node && IS_ENABLED(CONFIG_RESET_CONTROLLER) &&
> > >> > > +     !IS_ERR(drv_data->rstc))
> > >> > >           reset_control_assert(drv_data->rstc);
> > >> >
> > >> > Another question is... why do we need to check pd->dev.of_node here?
> > >> > If CONFIG_RESET_CONTROLLER is set, we always try to get the reset
> > >> > controller node, so drv_data->rstc is either going to be a valid
> > >> > pointer, or it's going to be an error pointer - neither
> > >> > reset_control_get() nor devm_reset_control_get return NULL.
> > >>
> > >> Following back on this as I was doing the patch, actually,
> > >> drv_data->rstc will be NULL if we're not probed by DT, and hence never
> > >> call reset_control_get, that would set an error pointer.
> > >>
> > >> But then, we can use IS_ERR_OR_NULL on drv_data->rstc.
> > >
> > > I think you can also move the devm_reset_control_get() into the main
> > > probe function: you're only checking for -EPROBE_DEFER from it to fail,
> > > allowing other errors to continue with the driver init.  This means
> > > that on non-OF, devm_reset_control_get() will fail with -ENOENT.
> > 
> > Looping linux-next into the CC since this is the cause of the failure
> > in orion5x_defconfig there, and no point in anyone else re-doing the
> > same bisect.
> 
> I sent a fix for this that hasn't been picked up yet:
> http://lists.infradead.org/pipermail/linux-arm-kernel/2014-March/239069.html
> 
> IIRC, Wolfram's away until Monday, so I guess it will be merged some
> time next week.

I think there is something wrong with an interface that makes you use
IS_ERR_OR_NULL(). If you are calling reset_control_get_optional(), that'
should not return an error when there is no reset controller listed
in the device tree. We should still have a way to propagate -EPROBE_DEFER,
or bail out if there is a reset controller but there is something wrong
with it, but otherwise I'd suggest just leaving NULL as a valid pointer
in drv_data->rstc and making sure that the reset controller functions
can just deal with a NULL argument, so you never have to check it again.

	Arnd
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