linux-kernel - Re: [PATCH v3] i2c: imx: make bus recovery through pinctrl optional

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Date:	Mon, 18 Jan 2016 09:37:04 +0100
From:	Uwe Kleine-König 
	<u.kleine-koenig@...gutronix.de>
To:	Li Yang <leoli@...escale.com>
Cc:	Gao Pan <pandy.gao@....com>, Wolfram Sang <wsa@...-dreams.de>,
	Linus Walleij <linus.walleij@...aro.org>,
	lkml <linux-kernel@...r.kernel.org>,
	Li Yang <leoyang.li@....com>, linux-gpio@...r.kernel.org,
	"linux-i2c@...r.kernel.org" <linux-i2c@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH v3] i2c: imx: make bus recovery through pinctrl optional

Hello Leo,

On Mon, Jan 18, 2016 at 04:22:51PM +0800, Li Yang wrote:
> On Fri, Jan 15, 2016 at 5:03 PM, Uwe Kleine-König
> <u.kleine-koenig@...gutronix.de> wrote:
> > On Fri, Jan 15, 2016 at 04:46:06PM +0800, Li Yang wrote:
> >> On Fri, Jan 15, 2016 at 3:53 PM, Uwe Kleine-König
> >> <u.kleine-koenig@...gutronix.de> wrote:
> >> >> -     i2c_imx_init_recovery_info(i2c_imx, pdev);
> >> >> +     if (IS_ERR_OR_NULL(i2c_imx->pinctrl))
> >> >
> >> > I'd prefer to set i2c_imx->pinctrl to NULL if it's not used and then use
> >> >
> >> >         if (!i2c_imx->pinctrl)
> >> >
> >> > here. (Or maybe make i2c_imx_init_recovery_info aware of this situation
> >> > to keep the caller simple?)
> >>
> >> Setting not used pointer to NULL might be a good coding practice
> >> generally.  But in this case neither the driver nor gpio framework
> >> checks if the pinctrl is NULL before accessing it.  We still need the
> >> driver to make sure pinctrl is not used in this situation.  The
> >> benefit of the proposed change seems to be pretty limited.  :)
> >
> > At least it gets rid of IS_ERR_OR_NULL which is used wrongly more often
> > than not.
> 
> It's true that this API is not used a lot.  Are you suggesting that it
> is poorly designed and probably should be removed?  But I still don't
> quite get the point why it tends to be wrongly used.  Do you consider
> the use in this patch a wrongly used case?

See http://permalink.gmane.org/gmane.linux.ports.arm.omap/97874 for an
earlier discussion. Having said that, I think at the moment there is no
such bug in this case, still I agree with Russell that IS_ERR_OR_NULL
isn't nice and so would prefer not to add new instances.

Best regards
Uwe


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