diff options
Diffstat (limited to 'Documentation')
| -rw-r--r-- | Documentation/DocBook/kernel-locking.tmpl | 6 | ||||
| -rw-r--r-- | Documentation/gpio.txt | 22 | ||||
| -rw-r--r-- | Documentation/mutex-design.txt | 3 |
3 files changed, 22 insertions, 9 deletions
diff --git a/Documentation/DocBook/kernel-locking.tmpl b/Documentation/DocBook/kernel-locking.tmpl index 0b1a3f9..a0d479d 100644 --- a/Documentation/DocBook/kernel-locking.tmpl +++ b/Documentation/DocBook/kernel-locking.tmpl @@ -1961,6 +1961,12 @@ machines due to caching. </sect1> </chapter> + <chapter id="apiref"> + <title>Mutex API reference</title> +!Iinclude/linux/mutex.h +!Ekernel/mutex.c + </chapter> + <chapter id="references"> <title>Further reading</title> diff --git a/Documentation/gpio.txt b/Documentation/gpio.txt index d96a6db..9633da0 100644 --- a/Documentation/gpio.txt +++ b/Documentation/gpio.txt @@ -109,17 +109,19 @@ use numbers 2000-2063 to identify GPIOs in a bank of I2C GPIO expanders. If you want to initialize a structure with an invalid GPIO number, use some negative number (perhaps "-EINVAL"); that will never be valid. To -test if a number could reference a GPIO, you may use this predicate: +test if such number from such a structure could reference a GPIO, you +may use this predicate: int gpio_is_valid(int number); A number that's not valid will be rejected by calls which may request or free GPIOs (see below). Other numbers may also be rejected; for -example, a number might be valid but unused on a given board. - -Whether a platform supports multiple GPIO controllers is currently a -platform-specific implementation issue. +example, a number might be valid but temporarily unused on a given board. +Whether a platform supports multiple GPIO controllers is a platform-specific +implementation issue, as are whether that support can leave "holes" in the space +of GPIO numbers, and whether new controllers can be added at runtime. Such issues +can affect things including whether adjacent GPIO numbers are both valid. Using GPIOs ----------- @@ -480,12 +482,16 @@ To support this framework, a platform's Kconfig will "select" either ARCH_REQUIRE_GPIOLIB or ARCH_WANT_OPTIONAL_GPIOLIB and arrange that its <asm/gpio.h> includes <asm-generic/gpio.h> and defines three functions: gpio_get_value(), gpio_set_value(), and gpio_cansleep(). -They may also want to provide a custom value for ARCH_NR_GPIOS. -ARCH_REQUIRE_GPIOLIB means that the gpio-lib code will always get compiled +It may also provide a custom value for ARCH_NR_GPIOS, so that it better +reflects the number of GPIOs in actual use on that platform, without +wasting static table space. (It should count both built-in/SoC GPIOs and +also ones on GPIO expanders. + +ARCH_REQUIRE_GPIOLIB means that the gpiolib code will always get compiled into the kernel on that architecture. -ARCH_WANT_OPTIONAL_GPIOLIB means the gpio-lib code defaults to off and the user +ARCH_WANT_OPTIONAL_GPIOLIB means the gpiolib code defaults to off and the user can enable it and build it into the kernel optionally. If neither of these options are selected, the platform does not support diff --git a/Documentation/mutex-design.txt b/Documentation/mutex-design.txt index c91ccc0..38c10fd 100644 --- a/Documentation/mutex-design.txt +++ b/Documentation/mutex-design.txt @@ -9,7 +9,7 @@ firstly, there's nothing wrong with semaphores. But if the simpler mutex semantics are sufficient for your code, then there are a couple of advantages of mutexes: - - 'struct mutex' is smaller on most architectures: .e.g on x86, + - 'struct mutex' is smaller on most architectures: E.g. on x86, 'struct semaphore' is 20 bytes, 'struct mutex' is 16 bytes. A smaller structure size means less RAM footprint, and better CPU-cache utilization. @@ -136,3 +136,4 @@ the APIs of 'struct mutex' have been streamlined: void mutex_lock_nested(struct mutex *lock, unsigned int subclass); int mutex_lock_interruptible_nested(struct mutex *lock, unsigned int subclass); + int atomic_dec_and_mutex_lock(atomic_t *cnt, struct mutex *lock); |
