Messages in this thread Patch in this message | | | From | David Brownell <> | Subject | [patch 2.6.29-rc3] gpio: gpio_{request,free}() now required (feature removal) | Date | Tue, 3 Feb 2009 14:35:22 -0800 |
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From: David Brownell <dbrownell@users.sourceforge.net>
We want to phase out the GPIO "autorequest" mechanism in gpiolib and require all callers to use gpio_request().
- Update feature-removal-schedule - Update the documentation now - Convert the relevant pr_warning() in gpiolib to a WARN() so folk using this mechanism get a noisy stack dump
Some drivers and board init code will probably need to change. Implementations not using gpiolib will still be fine; they are already required to implement gpio_{request,free}() stubs.
Signed-off-by: David Brownell <dbrownell@users.sourceforge.net> --- Documentation/feature-removal-schedule.txt | 12 ++++++++++++ Documentation/gpio.txt | 23 +++++++++-------------- drivers/gpio/gpiolib.c | 12 ++++++++---- 3 files changed, 29 insertions(+), 18 deletions(-)
--- a/Documentation/feature-removal-schedule.txt +++ b/Documentation/feature-removal-schedule.txt @@ -335,3 +335,15 @@ Why: In 2.6.18 the Secmark concept was i Secmark, it is time to deprecate the older mechanism and start the process of removing the old code. Who: Paul Moore <paul.moore@hp.com> + +--------------------------- + +What: GPIO autorequest on gpio_direction_{input,output}() in gpiolib +When: February 2010 +Why: All callers should use explicit gpio_request()/gpio_free(). + The autorequest mechanism in gpiolib was provided mostly as a + migration aid for legacy GPIO interfaces (for SOC based GPIOs). + Those users have now largely migrated. Platforms implementing + the GPIO interfaces without using gpiolib will see no changes. +Who: David Brownell <dbrownell@users.sourceforge.net> + --- a/Documentation/gpio.txt +++ b/Documentation/gpio.txt @@ -123,7 +123,10 @@ platform-specific implementation issue. Using GPIOs ----------- -One of the first things to do with a GPIO, often in board setup code when +The first thing a system should do with a GPIO is allocate it, using +the gpio_request() call; see later. + +One of the next things to do with a GPIO, often in board setup code when setting up a platform_device using the GPIO, is mark its direction: /* set as input or output, returning 0 or negative errno */ @@ -141,8 +144,8 @@ This helps avoid signal glitching during For compatibility with legacy interfaces to GPIOs, setting the direction of a GPIO implicitly requests that GPIO (see below) if it has not been -requested already. That compatibility may be removed in the future; -explicitly requesting GPIOs is strongly preferred. +requested already. That compatibility is being removed from the optional +gpiolib framework. Setting the direction can fail if the GPIO number is invalid, or when that particular GPIO can't be used in that mode. It's generally a bad @@ -195,7 +198,7 @@ This requires sleeping, which can't be d Platforms that support this type of GPIO distinguish them from other GPIOs by returning nonzero from this call (which requires a valid GPIO number, -either explicitly or implicitly requested): +which should have been previously allocated with gpio_request): int gpio_cansleep(unsigned gpio); @@ -212,10 +215,9 @@ for GPIOs that can't be accessed from IR same as the spinlock-safe calls. -Claiming and Releasing GPIOs (OPTIONAL) ---------------------------------------- +Claiming and Releasing GPIOs +---------------------------- To help catch system configuration errors, two calls are defined. -However, many platforms don't currently support this mechanism. /* request GPIO, returning 0 or negative errno. * non-null labels may be useful for diagnostics. @@ -244,13 +246,6 @@ Some platforms may also use knowledge ab power management, such as by powering down unused chip sectors and, more easily, gating off unused clocks. -These two calls are optional because not not all current Linux platforms -offer such functionality in their GPIO support; a valid implementation -could return success for all gpio_request() calls. Unlike the other calls, -the state they represent doesn't normally match anything from a hardware -register; it's just a software bitmap which clearly is not necessary for -correct operation of hardware or (bug free) drivers. - Note that requesting a GPIO does NOT cause it to be configured in any way; it just marks that GPIO as in use. Separate code must handle any pin setup (e.g. controlling which pin the GPIO uses, pullup/pulldown). --- a/drivers/gpio/gpiolib.c +++ b/drivers/gpio/gpiolib.c @@ -69,20 +69,24 @@ static inline void desc_set_label(struct * those calls have no teeth) we can't avoid autorequesting. This nag * message should motivate switching to explicit requests... so should * the weaker cleanup after faults, compared to gpio_request(). + * + * NOTE: the autorequest mechanism is going away; at this point it's + * only "legal" in the sense that (old) code using it won't break yet, + * but instead only triggers a WARN() stack dump. */ static int gpio_ensure_requested(struct gpio_desc *desc, unsigned offset) { - if (test_and_set_bit(FLAG_REQUESTED, &desc->flags) == 0) { - struct gpio_chip *chip = desc->chip; - int gpio = chip->base + offset; + const struct gpio_chip *chip = desc->chip; + const int gpio = chip->base + offset; + if (WARN(test_and_set_bit(FLAG_REQUESTED, &desc->flags) == 0, + "autorequest GPIO-%d\n", gpio)) { if (!try_module_get(chip->owner)) { pr_err("GPIO-%d: module can't be gotten \n", gpio); clear_bit(FLAG_REQUESTED, &desc->flags); /* lose */ return -EIO; } - pr_warning("GPIO-%d autorequested\n", gpio); desc_set_label(desc, "[auto]"); /* caller must chip->request() w/o spinlock */ if (chip->request)
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