linux-kernel - Re: [PATCH] gpio MIPS/OCTEON: Add a driver for OCTEON's on-chip GPIO pins.

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Date:	Thu, 20 Jun 2013 11:43:32 -0700
From:	Joe Perches <joe@...ches.com>
To:	David Daney <ddaney.cavm@...il.com>
Cc:	Linus Walleij <linus.walleij@...aro.org>,
	linux-mips@...ux-mips.org, Ralf Baechle <ralf@...ux-mips.org>,
	Grant Likely <grant.likely@...aro.org>,
	Rob Herring <rob.herring@...xeda.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"devicetree-discuss@...ts.ozlabs.org" 
	<devicetree-discuss@...ts.ozlabs.org>,
	David Daney <david.daney@...ium.com>
Subject: Re: [PATCH] gpio MIPS/OCTEON: Add a driver for OCTEON's on-chip
 GPIO pins.

On Thu, 2013-06-20 at 11:27 -0700, David Daney wrote:
> On 06/20/2013 11:18 AM, Joe Perches wrote:
> > On Thu, 2013-06-20 at 11:10 -0700, David Daney wrote:
> >> Sorry for not responding earlier, but my e-mail system seems to have
> >> malfunctioned with respect to this message...
> > []
> >> On 06/17/2013 01:51 AM, Linus Walleij wrote:
> >>>> +static int octeon_gpio_get(struct gpio_chip *chip, unsigned offset)
> >>>> +{
> >>>> +       struct octeon_gpio *gpio = container_of(chip, struct octeon_gpio, chip);
> >>>> +       u64 read_bits = cvmx_read_csr(gpio->register_base + RX_DAT);
> >>>> +
> >>>> +       return ((1ull << offset) & read_bits) != 0;
> >>>
> >>> A common idiom we use for this is:
> >>>
> >>> return !!(read_bits & (1ull << offset));
> >>
> >> I hate that idiom, but if its use is a condition of accepting the patch,
> >> I will change it.
> >
> > Or use an even more common idiom and change the
> > function to return bool and let the compiler do it.
> >
> 
> ... but it is part of the gpiochip system interface, so it would have to 
> be done kernel wide.

Not really.  It's a local static function.

> Really I don't like the idea of GPIO lines having Boolean truth values 
> associated with them.  Some represent things that are active-high and 
> others active-low.  Converting the pin voltage being above or below a 
> given threshold to something other than zero or one would in my opinion 
> be confusing.

No worries, just offering options.  Your code, your choice.

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