linux-kernel - Re: [RCF PATCH,v2,2/2] pwm: imx: Configure output to GPIO in disabled state

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Message-ID: <20181014202457.dohwgz3frgcpdpy6@pengutronix.de>
Date:   Sun, 14 Oct 2018 22:24:57 +0200
From:   Uwe Kleine-König 
        <u.kleine-koenig@...gutronix.de>
To:     Vokáč Michal <Michal.Vokac@...ft.com>
Cc:     Mark Rutland <mark.rutland@....com>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-pwm@...r.kernel.org" <linux-pwm@...r.kernel.org>,
        Lukasz Majewski <l.majewski@...ess.pl>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Thierry Reding <thierry.reding@...il.com>,
        "kernel@...gutronix.de" <kernel@...gutronix.de>,
        Fabio Estevam <fabio.estevam@....com>,
        Lothar Waßmann <LW@...o-electronics.de>
Subject: Re: [RCF PATCH,v2,2/2] pwm:
 imx: Configure output to GPIO in disabled state

Hello,

On Fri, Oct 12, 2018 at 06:08:54PM +0200, Uwe Kleine-König wrote:
> > >> +	if (PTR_ERR(imx_chip->pwm_gpiod) == -EPROBE_DEFER) {
> > > 
> > > You must not use PTR_ERR on a value that might not contain an error
> > > pointer.
> > 
> > OK, thank you for valuable info.
> > So it seems like the I2C folks are in troubles as well:
> > 
> > 	https://elixir.bootlin.com/linux/latest/source/drivers/i2c/busses/i2c-imx.c#L996
> 
> correct. I cannot find this documented though.

I found in LDD3[1], chapter 11 on page 295:

	If you need the actual error code, it can be extracted with:

		long PTR_ERR(const void *ptr);

	You should use PTR_ERR only on a value for which IS_ERR returns a true
	value; any other value is a valid pointer.

That is probably where I have my claim from. There is no further
explanation though, so I'll post a patch adding a comment to the
definition of PTR_ERR to find out if there is a relevant reason.

Best regards
Uwe

[1] https://lwn.net/Kernel/LDD3/

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