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Date: Fri, 18 Feb 2011 19:49:54 +0100
From: Uwe Kleine-König
<u.kleine-koenig@...gutronix.de>
To: Peter Tyser <ptyser@...-inc.com>
Cc: linux-kernel@...r.kernel.org, Alek Du <alek.du@...el.com>,
Samuel Ortiz <sameo@...ux.intel.com>,
David Brownell <dbrownell@...rs.sourceforge.net>,
Eric Miao <eric.y.miao@...il.com>,
Mark Brown <broonie@...nsource.wolfsonmicro.com>,
Joe Perches <joe@...ches.com>,
Alan Cox <alan@...rguk.ukuu.org.uk>,
Grant Likely <grant.likely@...retlab.ca>
Subject: Re: [PATCH v3 2/4] gpiolib: Add ability to get GPIO pin direction
Hello Peter,
On Fri, Feb 18, 2011 at 11:36:26AM -0600, Peter Tyser wrote:
> On Fri, 2011-02-18 at 09:57 +0100, Uwe Kleine-König wrote:
> > On Thu, Feb 17, 2011 at 05:03:17PM -0600, Peter Tyser wrote:
> > > Add a new get_direction() function to the gpio_chip structure. This is
> > > useful so that the direction of a pin can be determined when its
> > > initially exported. Previously, the direction defaulted to "unknown"
> > > regardless of the actual configuration of the GPIO pin.
> > >
> > > If a GPIO driver implements get_direction(), it is called in
> > > gpio_request() to set the initial direction of the pin accurately.
> > IMHO the commit log is conceptually wrong, because it talks about a
> > "pin". Better use gpio here.
>
> I don't follow. I used "pin" to make it clear that the get_direction()
> function operates on a pin-by-pin basis, and to help reduce any
> ambiguity about if a gpio chip or gpio pin is being referred to. Would
> you prefer that the "pin" references are clarified to be "GPIO pin"?
Maybe it's just that we use different terms. For me a "pin" is an
entry/exit point into/from a cpu or other chip. A gpio is (hmm, how
should I say) a concept how to drive a pin. A gpio might or might not
be "connected" to a pin at a given time.
> > > Cc: Alek Du <alek.du@...el.com>
> > > Cc: Samuel Ortiz <sameo@...ux.intel.com>
> > > Cc: David Brownell <dbrownell@...rs.sourceforge.net>
> > > Cc: Eric Miao <eric.y.miao@...il.com>
> > > Cc: Uwe Kleine-K?nig <u.kleine-koenig@...gutronix.de>
> > > Cc: Mark Brown <broonie@...nsource.wolfsonmicro.com>
> > > Cc: Joe Perches <joe@...ches.com>
> > > Cc: Alan Cox <alan@...rguk.ukuu.org.uk>
> > > Cc: Grant Likely <grant.likely@...retlab.ca>
> > > Signed-off-by: Peter Tyser <ptyser@...-inc.com>
> > > ---
> > > Changes since v1:
> > > - Add support for "unknown" direction
> > >
> > > Changes since v2:
> > > Based on Wolfram's feedback:
> > > - Use GPIOF_DIR_* flags as returns from get_direction()
> > > - Call spin_lock_irqsave() to before setting flags
> > >
> > > drivers/gpio/gpiolib.c | 23 +++++++++++++++++++++++
> > > include/asm-generic/gpio.h | 4 ++++
> > > 2 files changed, 27 insertions(+), 0 deletions(-)
> > >
> > > diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c
> > > index eb74311..a656a2c 100644
> > > --- a/drivers/gpio/gpiolib.c
> > > +++ b/drivers/gpio/gpiolib.c
> > > @@ -1174,6 +1174,7 @@ int gpio_request(unsigned gpio, const char *label)
> > > struct gpio_desc *desc;
> > > struct gpio_chip *chip;
> > > int status = -EINVAL;
> > > + int dir;
> > > unsigned long flags;
> > >
> > > spin_lock_irqsave(&gpio_lock, flags);
> > > @@ -1214,6 +1215,28 @@ int gpio_request(unsigned gpio, const char *label)
> > > }
> > > }
> > >
> > > + if (chip->get_direction) {
> > > + /* chip->get_direction may sleep */
> > > + spin_unlock_irqrestore(&gpio_lock, flags);
> > might_sleep_if(chip->can_sleep) ?
>
> Makes sense. I was following the lead of chip->request() in the same
> function, which doesn't use might_sleep_if(). I assume might_sleep_if()
> should be added to it as well in a separate patch?
I was there first :-)
http://mid.gmane.org/1297977533-17794-1-git-send-email-u.kleine-koenig@pengutronix.de
> > > + dir = chip->get_direction(chip, gpio - chip->base);
> > > + spin_lock_irqsave(&gpio_lock, flags);
> > > + switch (dir) {
> > > + case GPIOF_DIR_OUT:
> > > + set_bit(FLAG_DIR_OUT, &desc->flags);
> > > + clear_bit(FLAG_DIR_IN, &desc->flags);
> > > + break;
> > > + case GPIOF_DIR_IN:
> > > + set_bit(FLAG_DIR_IN, &desc->flags);
> > > + clear_bit(FLAG_DIR_OUT, &desc->flags);
> > > + break;
> > > + default:
> > > + /* Direction isn't known */
> > > + clear_bit(FLAG_DIR_OUT, &desc->flags);
> > > + clear_bit(FLAG_DIR_IN, &desc->flags);
> > > + break;
> > > + }
> > Alternatively to my suggestion for patch1:
> > } else {
> > clear_bit(FLAG_DIR_OUT, &desc->flags);
> > clear_bit(FLAG_DIR_IN, &desc->flags);
>
> I like this way better too. I'll initialize dir = -1 and pull the
> switch statement out of the conditional, like:
>
> if (chip->get_direction) {
> /* chip->get_direction may sleep */
> spin_unlock_irqrestore(&gpio_lock, flags);
> might_sleep_if(chip->can_sleep);
> dir = chip->get_direction(chip, gpio - chip->base);
> spin_lock_irqsave(&gpio_lock, flags);
> }
>
> switch (dir) {
> case GPIOF_DIR_OUT:
> set_bit(FLAG_DIR_OUT, &desc->flags);
> clear_bit(FLAG_DIR_IN, &desc->flags);
> break;
> case GPIOF_DIR_IN:
> set_bit(FLAG_DIR_IN, &desc->flags);
> clear_bit(FLAG_DIR_OUT, &desc->flags);
> break;
> default:
> /* Direction isn't known */
> clear_bit(FLAG_DIR_OUT, &desc->flags);
> clear_bit(FLAG_DIR_IN, &desc->flags);
> break;
> }
fine
Uwe
--
Pengutronix e.K. | Uwe Kleine-König |
Industrial Linux Solutions | http://www.pengutronix.de/ |
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