GPIO update to allow code to get at gpio_chip
Subsystems (3)
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 1/1 gpiolib: add gpio_lookup_chip() to get chip information for gpio
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.
--- drivers/gpio/gpiolib.c | 26 ++++++++++++++++++++++++++ include/asm-generic/gpio.h | 2 ++ 2 files changed, 28 insertions(+), 0 deletions(-)
drivers/gpio/gpiolib.c +26 -0
@@ -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) {
include/asm-generic/gpio.h +2 -0
@@ -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);
Signature · 1 line
1.6.0.4
Re: [PATCH] gpiolib: add gpio_lookup_chip() to get chip information for gpio
Quoted 9 lines · 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 thegpio_chipthat 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.
Re: [PATCH] gpiolib: add gpio_lookup_chip() to get chip information for gpio
Quoted 6 lines · Eric Miao
Quoted 5 lines · 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 thegpio_chipthat they registered without having to have their own list of gpio.
Quoted 8 lines
Quoted 4 lines
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.
Signature · 4 lines
Ben Q: What's a light-year? A: One-third less calories than a regular year.
Re: [PATCH] gpiolib: add gpio_lookup_chip() to get chip information for gpio
In reply to Ben DooksQuoted 27 lines · On Fri, 8 Jan 2010 06:32:28 +0000 Ben Dooks <[email protected]> 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 thegpio_chipthat 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.
...
drivers/gpio/gpiolib.c +16
-0+/** +* 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; +
drivers/gpio/gpiolib.c static inline struct gpio_chip *gpio_to_chip(unsigned gpio) · line 148
Quoted 10 lines
drivers/gpio/gpiolib.c +10
-0+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.