linux-kernel - Re: [RFC 2.6.28 1/2] gpiolib: add set/get batch v4

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Date:	Mon, 19 Jan 2009 18:25:36 +0100
From:	Uwe Kleine-König 
	<u.kleine-koenig@...gutronix.de>
To:	Jaya Kumar <jayakumar.lkml@...il.com>
Cc:	David Brownell <david-b@...bell.net>,
	Eric Miao <eric.miao@...vell.com>,
	Paulius Zaleckas <paulius.zaleckas@...tonika.lt>,
	Geert Uytterhoeven <geert@...ux-m68k.org>,
	Sam Ravnborg <sam@...nborg.org>,
	linux-arm-kernel@...ts.arm.linux.org.uk,
	linux-fbdev-devel@...ts.sourceforge.net,
	linux-kernel@...r.kernel.org, linux-embedded@...r.kernel.org
Subject: Re: [RFC 2.6.28 1/2] gpiolib: add set/get batch v4

Hi Jaya,

> >> +[OPTIONAL] Spinlock-Safe GPIO Batch access
> > Is it really spinlock safe in general?  Or only if gpio_cansleep(gpio)
> > if false for each gpio to get or set?
> 
> You are correct to raise this issue. It is only spinlock safe if
> chip->cansleep is false. Initially, I wasn't sure what to do. The
> original gpio set/get_value() just does;
>         WARN_ON(extra_checks && chip->can_sleep);
> and it is documented as:
> 
> "
> Spinlock-Safe GPIO access
> -------------------------
> <snip>
> return zero.  Also, using these calls for GPIOs that can't safely be accessed
> without sleeping (see below) is an error.
> "
> 
> I will change this in the batch code to return an error if can_sleep
> is detected on any involved gpio_chip.
Wait, I got it wrong.  I thought gpio_set_value might sleep if
chip->cansleep is true, but there are extra API functions for
cansleep-chips.  So I'd do it the same way as for the non-batch
functions and just WARN_ON(extra_checks && chip->cansleep) for each
involved chip.

Later it might make sense to add the _cansleep variants.

Best regards
Uwe
-- 
Pengutronix e.K.                              | Uwe Kleine-König            |
Industrial Linux Solutions                    | http://www.pengutronix.de/  |
Peiner Strasse 6-8, 31137 Hildesheim, Germany | Phone: +49-5121-206917-0    |
Amtsgericht Hildesheim, HRA 2686              | Fax:   +49-5121-206917-5555 |
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