GPIO update to allow code to get at gpio_chip

GPIO update to allow code to get at gpio_chip

[Ben Dooks]

Allowing gpiolib implementations to get at the gpio_chip from the
gpio number is useful to allow gpiolib gpio numbering to be used
for other gpio purposes such as changing pin configuration.

The following patch exports this information. A patch showing the
reason for my wanting this can be supplied on request.

[PATCH] gpiolib: add gpio_lookup_chip() to get chip information for gpio

[Ben Dooks]

Add a call to get the 'struct gpio_chip' pointer for a given gpio, so
that core implementations which want to use gpiolib gpio numbering for
things like mux configuration can get back to the gpio_chip that they
registered without having to have their own list of gpio.

This is especially useful for the Samsung S3C64XX series where the GPIO
bank sizes can vary from 32 down to 3, making it difficult to store an
array to convert a number to chip.

Signed-off-by: Ben Dooks <ben-linux@fluff.org>
---
 drivers/gpio/gpiolib.c     |   26 ++++++++++++++++++++++++++
 include/asm-generic/gpio.h |    2 ++
 2 files changed, 28 insertions(+), 0 deletions(-)

diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c
index a25ad28..d748600 100644
--- a/drivers/gpio/gpiolib.c
+++ b/drivers/gpio/gpiolib.c
@@ -120,6 +120,32 @@ static inline struct gpio_chip *gpio_to_chip(unsigned gpio)
 	return gpio_desc[gpio].chip;
 }
 
+/**
+ * gpio_lookup_chip - return the chip for a given gpio
+ * @gpio: The GPIO number to lookup
+ *
+ * Returns NULL if the GPIO chip is not valid or there is no chip registered
+ * for that GPIO. This call is available for core code to turn a GPIO number
+ * into a chip so that further information can be looked up.
+ *
+ * This call makes no guarantees about the actuall gpio_chip's state, or
+ * whether the @gpio itself is requested.
+ */
+struct gpio_chip *gpio_lookup_chip(unsigned gpio)
+{
+	struct gpio_chip *chip;
+	unsigned long flags;
+
+	if (!gpio_is_valid(gpio))
+		return NULL;
+
+	spin_lock_irqsave(&gpio_lock, flags);
+	chip = gpio_to_chip(gpio);
+	spin_unlock_irqrestore(&gpio_lock, flags);
+
+	return chip;
+}
+
 /* dynamic allocation of GPIOs, e.g. on a hotplugged device */
 static int gpiochip_find_base(int ngpio)
 {
diff --git a/include/asm-generic/gpio.h b/include/asm-generic/gpio.h
index 485eeb6..34b3276 100644
--- a/include/asm-generic/gpio.h
+++ b/include/asm-generic/gpio.h
@@ -103,6 +103,8 @@ struct gpio_chip {
 	unsigned		exported:1;
 };
 
+extern struct gpio_chip *gpio_lookup_chip(unsigned gpio);
+
 extern const char *gpiochip_is_requested(struct gpio_chip *chip,
 			unsigned offset);
 extern int __must_check gpiochip_reserve(int start, int ngpio);
-- 
1.6.0.4

[PATCH] gpiolib: add gpio_lookup_chip() to get chip information for gpio

[Eric Miao]

On Fri, Jan 8, 2010 at 2:32 PM, Ben Dooks <ben-linux@fluff.org> wrote:
> Add a call to get the 'struct gpio_chip' pointer for a given gpio, so
> that core implementations which want to use gpiolib gpio numbering for
> things like mux configuration can get back to the gpio_chip that they
> registered without having to have their own list of gpio.
>
> This is especially useful for the Samsung S3C64XX series where the GPIO
> bank sizes can vary from 32 down to 3, making it difficult to store an
> array to convert a number to chip.
>

I think this is generally a good idea. Will most likely be useful to
pxa platforms as well. Not sure though if you want to export this
symbol as well since we do allow gpio chip drivers to be modules.

[PATCH] gpiolib: add gpio_lookup_chip() to get chip information for gpio

[Ben Dooks]

On Fri, Jan 08, 2010 at 03:30:36PM +0800, Eric Miao wrote:
> On Fri, Jan 8, 2010 at 2:32 PM, Ben Dooks <ben-linux@fluff.org> wrote:
> > Add a call to get the 'struct gpio_chip' pointer for a given gpio, so
> > that core implementations which want to use gpiolib gpio numbering for
> > things like mux configuration can get back to the gpio_chip that they
> > registered without having to have their own list of gpio.
> >
> > This is especially useful for the Samsung S3C64XX series where the GPIO
> > bank sizes can vary from 32 down to 3, making it difficult to store an
> > array to convert a number to chip.
> >
> 
> I think this is generally a good idea. Will most likely be useful to
> pxa platforms as well. Not sure though if you want to export this
> symbol as well since we do allow gpio chip drivers to be modules.

Probably not, since all the gpio call methods pass gpio_chip as their
first parameter. This is only in the case we want to use gpios for
something other than in/out/irq.

-- 
Ben

Q:      What's a light-year?
A:      One-third less calories than a regular year.

[PATCH] gpiolib: add gpio_lookup_chip() to get chip information for gpio

[Andrew Morton]

On Fri,  8 Jan 2010 06:32:28 +0000 Ben Dooks <ben-linux@fluff.org> wrote:

> Add a call to get the 'struct gpio_chip' pointer for a given gpio, so
> that core implementations which want to use gpiolib gpio numbering for
> things like mux configuration can get back to the gpio_chip that they
> registered without having to have their own list of gpio.
> 
> This is especially useful for the Samsung S3C64XX series where the GPIO
> bank sizes can vary from 32 down to 3, making it difficult to store an
> array to convert a number to chip.
> 
> ...
>  
> +/**
> + * gpio_lookup_chip - return the chip for a given gpio
> + * @gpio: The GPIO number to lookup
> + *
> + * Returns NULL if the GPIO chip is not valid or there is no chip registered
> + * for that GPIO. This call is available for core code to turn a GPIO number
> + * into a chip so that further information can be looked up.
> + *
> + * This call makes no guarantees about the actuall gpio_chip's state, or
> + * whether the @gpio itself is requested.
> + */
> +struct gpio_chip *gpio_lookup_chip(unsigned gpio)
> +{
> +	struct gpio_chip *chip;
> +	unsigned long flags;
> +
> +	if (!gpio_is_valid(gpio))
> +		return NULL;
> +
> +	spin_lock_irqsave(&gpio_lock, flags);
> +	chip = gpio_to_chip(gpio);
> +	spin_unlock_irqrestore(&gpio_lock, flags);
> +
> +	return chip;
> +}
> +

The locking looks fishy.  What's the point in locking the array lookup and
then returning the thing which was looked up after dropping the lock?

Should this function have been exported to modules?

Please cc myself and David Brownell on gpio patches.