diff options
Diffstat (limited to 'Documentation/driver-api/gpio/driver.rst')
| -rw-r--r-- | Documentation/driver-api/gpio/driver.rst | 43 |
1 files changed, 21 insertions, 22 deletions
diff --git a/Documentation/driver-api/gpio/driver.rst b/Documentation/driver-api/gpio/driver.rst index 6baaeab79534..85d86f92c41b 100644 --- a/Documentation/driver-api/gpio/driver.rst +++ b/Documentation/driver-api/gpio/driver.rst @@ -7,7 +7,7 @@ This document serves as a guide for writers of GPIO chip drivers. Each GPIO controller driver needs to include the following header, which defines the structures used to define a GPIO driver:: - #include <linux/gpio/driver.h> + #include <linux/gpio/driver.h> Internal Representation of GPIOs @@ -69,9 +69,8 @@ driver code: The code implementing a gpio_chip should support multiple instances of the controller, preferably using the driver model. That code will configure each -gpio_chip and issue gpiochip_add(), gpiochip_add_data(), or -devm_gpiochip_add_data(). Removing a GPIO controller should be rare; use -gpiochip_remove() when it is unavoidable. +gpio_chip and issue gpiochip_add_data() or devm_gpiochip_add_data(). Removing +a GPIO controller should be rare; use gpiochip_remove() when it is unavoidable. Often a gpio_chip is part of an instance-specific structure with states not exposed by the GPIO interfaces, such as addressing, power management, and more. @@ -144,7 +143,7 @@ is not open, it will present a high-impedance (tristate) to the external rail:: in ----|| |/ ||--+ in ----| | |\ - GND GND + GND GND This configuration is normally used as a way to achieve one of two things: @@ -218,10 +217,10 @@ not support open drain/open source in hardware, the GPIO library will instead use a trick: when a line is set as output, if the line is flagged as open drain, and the IN output value is low, it will be driven low as usual. But if the IN output value is set to high, it will instead *NOT* be driven high, -instead it will be switched to input, as input mode is high impedance, thus -achieving an "open drain emulation" of sorts: electrically the behaviour will -be identical, with the exception of possible hardware glitches when switching -the mode of the line. +instead it will be switched to input, as input mode is an equivalent to +high impedance, thus achieving an "open drain emulation" of sorts: electrically +the behaviour will be identical, with the exception of possible hardware glitches +when switching the mode of the line. For open source configuration the same principle is used, just that instead of actively driving the line low, it is set to input. @@ -550,10 +549,10 @@ the interrupt separately and go with it: struct my_gpio *g; struct gpio_irq_chip *girq; - ret = devm_request_threaded_irq(dev, irq, NULL, - irq_thread_fn, IRQF_ONESHOT, "my-chip", g); + ret = devm_request_threaded_irq(dev, irq, NULL, irq_thread_fn, + IRQF_ONESHOT, "my-chip", g); if (ret < 0) - return ret; + return ret; /* Get a pointer to the gpio_irq_chip */ girq = &g->gc.irq; @@ -681,12 +680,12 @@ certain operations and keep track of usage inside of the gpiolib subsystem. Input GPIOs can be used as IRQ signals. When this happens, a driver is requested to mark the GPIO as being used as an IRQ:: - int gpiochip_lock_as_irq(struct gpio_chip *chip, unsigned int offset) + int gpiochip_lock_as_irq(struct gpio_chip *chip, unsigned int offset) This will prevent the use of non-irq related GPIO APIs until the GPIO IRQ lock is released:: - void gpiochip_unlock_as_irq(struct gpio_chip *chip, unsigned int offset) + void gpiochip_unlock_as_irq(struct gpio_chip *chip, unsigned int offset) When implementing an irqchip inside a GPIO driver, these two functions should typically be called in the .startup() and .shutdown() callbacks from the @@ -708,12 +707,12 @@ When a GPIO is used as an IRQ signal, then gpiolib also needs to know if the IRQ is enabled or disabled. In order to inform gpiolib about this, the irqchip driver should call:: - void gpiochip_disable_irq(struct gpio_chip *chip, unsigned int offset) + void gpiochip_disable_irq(struct gpio_chip *chip, unsigned int offset) This allows drivers to drive the GPIO as an output while the IRQ is disabled. When the IRQ is enabled again, a driver should call:: - void gpiochip_enable_irq(struct gpio_chip *chip, unsigned int offset) + void gpiochip_enable_irq(struct gpio_chip *chip, unsigned int offset) When implementing an irqchip inside a GPIO driver, these two functions should typically be called in the .irq_disable() and .irq_enable() callbacks from the @@ -751,7 +750,7 @@ compliance: - Test your driver with the appropriate in-kernel real-time test cases for both level and edge IRQs -* [1] http://www.spinics.net/lists/linux-omap/msg120425.html +* [1] https://lore.kernel.org/r/1437496011-11486-1-git-send-email-bigeasy@linutronix.de/ * [2] https://lore.kernel.org/r/1443209283-20781-2-git-send-email-grygorii.strashko@ti.com * [3] https://lore.kernel.org/r/1443209283-20781-3-git-send-email-grygorii.strashko@ti.com @@ -763,12 +762,12 @@ Sometimes it is useful to allow a GPIO chip driver to request its own GPIO descriptors through the gpiolib API. A GPIO driver can use the following functions to request and free descriptors:: - struct gpio_desc *gpiochip_request_own_desc(struct gpio_desc *desc, - u16 hwnum, - const char *label, - enum gpiod_flags flags) + struct gpio_desc *gpiochip_request_own_desc(struct gpio_desc *desc, + u16 hwnum, + const char *label, + enum gpiod_flags flags) - void gpiochip_free_own_desc(struct gpio_desc *desc) + void gpiochip_free_own_desc(struct gpio_desc *desc) Descriptors requested with gpiochip_request_own_desc() must be released with gpiochip_free_own_desc(). |