Re: gpiolib and sleeping gpios

[Jani Nikula]

On Sat, 19 Jun 2010, ext David Brownell wrote:

> > The point I was trying to make is that there are lots of drivers which 
> > will not work with gpios on sleeping io expanders because they call the 
> > spinlock safe gpio calls.
>
> And they will trigger runtime warnings, and thus eventually get fixed. 
> The way to do that is to check if the GPIO needs the cansleep() call
>
> That's the first category above:  the driver should have used the 
> cansleep() variant, and sotriggers a runtime warning.

Hi David -

Part of the reason why such drivers haven't been fixed might be that the 
runtime warnings are only issued if DEBUG is defined in gpiolib.c:

/* When debugging, extend minimal trust to callers and platform code.
 * Also emit diagnostic messages that may help initial bringup, when
 * board setup or driver bugs are most common.
 *
 * Otherwise, minimize overhead in what may be bitbanging codepaths.
 */
#ifdef	DEBUG
#define	extra_checks	1
#else
#define	extra_checks	0
#endif

...

int __gpio_get_value(unsigned gpio)
{
	struct gpio_chip	*chip;

	chip = gpio_to_chip(gpio);
	WARN_ON(extra_checks && chip->can_sleep);
	return chip->get ? chip->get(chip, gpio - chip->base) : 0;
}

Do you think it would do more harm than good to unconditionally enable the 
extra checks? I do see the comment about overhead there, but having them 
enabled would probably aid driver developers in fixing existing code and 
choosing the correct calls in the future.


BR,
Jani.
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