diff options
Diffstat (limited to 'Documentation/driver-api/gpio')
| -rw-r--r-- | Documentation/driver-api/gpio/board.rst | 38 | ||||
| -rw-r--r-- | Documentation/driver-api/gpio/consumer.rst | 57 | ||||
| -rw-r--r-- | Documentation/driver-api/gpio/driver.rst | 272 | ||||
| -rw-r--r-- | Documentation/driver-api/gpio/drivers-on-gpio.rst | 21 | ||||
| -rw-r--r-- | Documentation/driver-api/gpio/index.rst | 1 | ||||
| -rw-r--r-- | Documentation/driver-api/gpio/intro.rst | 16 | ||||
| -rw-r--r-- | Documentation/driver-api/gpio/legacy.rst | 78 | ||||
| -rw-r--r-- | Documentation/driver-api/gpio/using-gpio.rst | 50 |
8 files changed, 334 insertions, 199 deletions
diff --git a/Documentation/driver-api/gpio/board.rst b/Documentation/driver-api/gpio/board.rst index ce91518bf9f4..b33aa04f213f 100644 --- a/Documentation/driver-api/gpio/board.rst +++ b/Documentation/driver-api/gpio/board.rst @@ -6,7 +6,7 @@ This document explains how GPIOs can be assigned to given devices and functions. Note that it only applies to the new descriptor-based interface. For a description of the deprecated integer-based GPIO interface please refer to -gpio-legacy.txt (actually, there is no real mapping possible with the old +legacy.rst (actually, there is no real mapping possible with the old interface; you just fetch an integer from somewhere and request the corresponding GPIO). @@ -71,14 +71,14 @@ with the help of _DSD (Device Specific Data), introduced in ACPI 5.1:: Device (FOO) { Name (_CRS, ResourceTemplate () { - GpioIo (Exclusive, ..., IoRestrictionOutputOnly, - "\\_SB.GPI0") {15} // red - GpioIo (Exclusive, ..., IoRestrictionOutputOnly, - "\\_SB.GPI0") {16} // green - GpioIo (Exclusive, ..., IoRestrictionOutputOnly, - "\\_SB.GPI0") {17} // blue - GpioIo (Exclusive, ..., IoRestrictionOutputOnly, - "\\_SB.GPI0") {1} // power + GpioIo (Exclusive, PullUp, 0, 0, IoRestrictionOutputOnly, + "\\_SB.GPI0", 0, ResourceConsumer) { 15 } // red + GpioIo (Exclusive, PullUp, 0, 0, IoRestrictionOutputOnly, + "\\_SB.GPI0", 0, ResourceConsumer) { 16 } // green + GpioIo (Exclusive, PullUp, 0, 0, IoRestrictionOutputOnly, + "\\_SB.GPI0", 0, ResourceConsumer) { 17 } // blue + GpioIo (Exclusive, PullNone, 0, 0, IoRestrictionOutputOnly, + "\\_SB.GPI0", 0, ResourceConsumer) { 1 } // power }) Name (_DSD, Package () { @@ -92,10 +92,7 @@ with the help of _DSD (Device Specific Data), introduced in ACPI 5.1:: ^FOO, 2, 0, 1, } }, - Package () { - "power-gpios", - Package () {^FOO, 3, 0, 0}, - }, + Package () { "power-gpios", Package () { ^FOO, 3, 0, 0 } }, } }) } @@ -113,13 +110,15 @@ files that desire to do so need to include the following header:: GPIOs are mapped by the means of tables of lookups, containing instances of the gpiod_lookup structure. Two macros are defined to help declaring such mappings:: - GPIO_LOOKUP(chip_label, chip_hwnum, con_id, flags) - GPIO_LOOKUP_IDX(chip_label, chip_hwnum, con_id, idx, flags) + GPIO_LOOKUP(key, chip_hwnum, con_id, flags) + GPIO_LOOKUP_IDX(key, chip_hwnum, con_id, idx, flags) where - - chip_label is the label of the gpiod_chip instance providing the GPIO - - chip_hwnum is the hardware number of the GPIO within the chip + - key is either the label of the gpiod_chip instance providing the GPIO, or + the GPIO line name + - chip_hwnum is the hardware number of the GPIO within the chip, or U16_MAX + to indicate that key is a GPIO line name - con_id is the name of the GPIO function from the device point of view. It can be NULL, in which case it will match any function. - idx is the index of the GPIO within the function. @@ -135,7 +134,10 @@ where In the future, these flags might be extended to support more properties. -Note that GPIO_LOOKUP() is just a shortcut to GPIO_LOOKUP_IDX() where idx = 0. +Note that: + 1. GPIO line names are not guaranteed to be globally unique, so the first + match found will be used. + 2. GPIO_LOOKUP() is just a shortcut to GPIO_LOOKUP_IDX() where idx = 0. A lookup table can then be defined as follows, with an empty entry defining its end. The 'dev_id' field of the table is the identifier of the device that will diff --git a/Documentation/driver-api/gpio/consumer.rst b/Documentation/driver-api/gpio/consumer.rst index 423492d125b9..ab56ab0dd7a6 100644 --- a/Documentation/driver-api/gpio/consumer.rst +++ b/Documentation/driver-api/gpio/consumer.rst @@ -4,7 +4,7 @@ GPIO Descriptor Consumer Interface This document describes the consumer interface of the GPIO framework. Note that it describes the new descriptor-based interface. For a description of the -deprecated integer-based GPIO interface please refer to gpio-legacy.txt. +deprecated integer-based GPIO interface please refer to legacy.rst. Guidelines for GPIOs consumers @@ -12,7 +12,7 @@ Guidelines for GPIOs consumers Drivers that can't work without standard GPIO calls should have Kconfig entries that depend on GPIOLIB or select GPIOLIB. The functions that allow a driver to -obtain and use GPIOs are available by including the following file: +obtain and use GPIOs are available by including the following file:: #include <linux/gpio/consumer.h> @@ -29,6 +29,10 @@ warnings. These stubs are used for two use cases: will use it under other compile-time configurations. In this case the consumer must make sure not to call into these functions, or the user will be met with console warnings that may be perceived as intimidating. + Combining truly optional GPIOLIB usage with calls to + ``[devm_]gpiod_get_optional()`` is a *bad idea*, and will result in weird + error messages. Use the ordinary getter functions with optional GPIOLIB: + some open coding of error handling should be expected when you do this. All the functions that work with the descriptor-based GPIO interface are prefixed with ``gpiod_``. The ``gpio_`` prefix is used for the legacy @@ -72,9 +76,13 @@ for the GPIO. Values can be: * GPIOD_OUT_HIGH_OPEN_DRAIN same as GPIOD_OUT_HIGH but also enforce the line to be electrically used with open drain. +Note that the initial value is *logical* and the physical line level depends on +whether the line is configured active high or active low (see +:ref:`active_low_semantics`). + The two last flags are used for use cases where open drain is mandatory, such as I2C: if the line is not already configured as open drain in the mappings -(see board.txt), then open drain will be enforced anyway and a warning will be +(see board.rst), then open drain will be enforced anyway and a warning will be printed that the board configuration needs to be updated to match the use case. Both functions return either a valid GPIO descriptor, or an error code checkable @@ -110,7 +118,7 @@ For a function using multiple GPIOs all of those can be obtained with one call:: This function returns a struct gpio_descs which contains an array of descriptors. It also contains a pointer to a gpiolib private structure which, -if passed back to get/set array functions, may speed up I/O proocessing:: +if passed back to get/set array functions, may speed up I/O processing:: struct gpio_descs { struct gpio_array *info; @@ -214,9 +222,9 @@ Use the following calls to access GPIOs from an atomic context:: int gpiod_get_value(const struct gpio_desc *desc); void gpiod_set_value(struct gpio_desc *desc, int value); -The values are boolean, zero for low, nonzero for high. When reading the value -of an output pin, the value returned should be what's seen on the pin. That -won't always match the specified output value, because of issues including +The values are boolean, zero for inactive, nonzero for active. When reading the +value of an output pin, the value returned should be what's seen on the pin. +That won't always match the specified output value, because of issues including open-drain signaling and output latencies. The get/set calls do not return errors because "invalid GPIO" should have been @@ -252,6 +260,8 @@ that can't be accessed from hardIRQ handlers, these calls act the same as the spinlock-safe calls. +.. _active_low_semantics: + The active low and open drain semantics --------------------------------------- As a consumer should not have to care about the physical line level, all of the @@ -264,14 +274,14 @@ driven. The same is applicable for open drain or open source output lines: those do not actively drive their output high (open drain) or low (open source), they just switch their output to a high impedance value. The consumer should not need to -care. (For details read about open drain in driver.txt.) +care. (For details read about open drain in driver.rst.) With this, all the gpiod_set_(array)_value_xxx() functions interpret the -parameter "value" as "asserted" ("1") or "de-asserted" ("0"). The physical line +parameter "value" as "active" ("1") or "inactive" ("0"). The physical line level will be driven accordingly. As an example, if the active low property for a dedicated GPIO is set, and the -gpiod_set_(array)_value_xxx() passes "asserted" ("1"), the physical line level +gpiod_set_(array)_value_xxx() passes "active" ("1"), the physical line level will be driven low. To summarize:: @@ -309,9 +319,11 @@ work on the raw line value:: void gpiod_set_raw_value_cansleep(struct gpio_desc *desc, int value) int gpiod_direction_output_raw(struct gpio_desc *desc, int value) -The active low state of a GPIO can also be queried using the following call:: +The active low state of a GPIO can also be queried and toggled using the +following calls:: int gpiod_is_active_low(const struct gpio_desc *desc) + void gpiod_toggle_active_low(struct gpio_desc *desc) Note that these functions should only be used with great moderation; a driver should not have to care about the physical line level or open drain semantics. @@ -361,12 +373,13 @@ corresponding chip driver. In that case a significantly improved performance can be expected. If simultaneous access is not possible the GPIOs will be accessed sequentially. -The functions take three arguments: +The functions take four arguments: + * array_size - the number of array elements * desc_array - an array of GPIO descriptors * array_info - optional information obtained from gpiod_get_array() * value_bitmap - a bitmap to store the GPIOs' values (get) or - a bitmap of values to assign to the GPIOs (set) + a bitmap of values to assign to the GPIOs (set) The descriptor array can be obtained using the gpiod_get_array() function or one of its variants. If the group of descriptors returned by that function @@ -440,18 +453,20 @@ For details refer to Documentation/firmware-guide/acpi/gpio-properties.rst Interacting With the Legacy GPIO Subsystem ========================================== -Many kernel subsystems still handle GPIOs using the legacy integer-based -interface. Although it is strongly encouraged to upgrade them to the safer -descriptor-based API, the following two functions allow you to convert a GPIO -descriptor into the GPIO integer namespace and vice-versa:: +Many kernel subsystems and drivers still handle GPIOs using the legacy +integer-based interface. It is strongly recommended to update these to the new +gpiod interface. For cases where both interfaces need to be used, the following +two functions allow to convert a GPIO descriptor into the GPIO integer namespace +and vice-versa:: int desc_to_gpio(const struct gpio_desc *desc) struct gpio_desc *gpio_to_desc(unsigned gpio) -The GPIO number returned by desc_to_gpio() can be safely used as long as the -GPIO descriptor has not been freed. All the same, a GPIO number passed to -gpio_to_desc() must have been properly acquired, and usage of the returned GPIO -descriptor is only possible after the GPIO number has been released. +The GPIO number returned by desc_to_gpio() can safely be used as a parameter of +the gpio\_*() functions for as long as the GPIO descriptor `desc` is not freed. +All the same, a GPIO number passed to gpio_to_desc() must first be properly +acquired using e.g. gpio_request_one(), and the returned GPIO descriptor is only +considered valid until that GPIO number is released using gpio_free(). Freeing a GPIO obtained by one API with the other API is forbidden and an unchecked error. diff --git a/Documentation/driver-api/gpio/driver.rst b/Documentation/driver-api/gpio/driver.rst index 2ff743105927..bf6319cc531b 100644 --- a/Documentation/driver-api/gpio/driver.rst +++ b/Documentation/driver-api/gpio/driver.rst @@ -119,7 +119,7 @@ GPIO lines with debounce support Debouncing is a configuration set to a pin indicating that it is connected to a mechanical switch or button, or similar that may bounce. Bouncing means the line is pulled high/low quickly at very short intervals for mechanical -reasons. This can result in the value being unstable or irqs fireing repeatedly +reasons. This can result in the value being unstable or irqs firing repeatedly unless the line is debounced. Debouncing in practice involves setting up a timer when something happens on @@ -218,10 +218,10 @@ 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 -achieveing 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. @@ -342,12 +342,12 @@ Cascaded GPIO irqchips usually fall in one of three categories: forced to a thread. The "fake?" raw lock can be used to work around this problem:: - raw_spinlock_t wa_lock; - static irqreturn_t omap_gpio_irq_handler(int irq, void *gpiobank) - unsigned long wa_lock_flags; - raw_spin_lock_irqsave(&bank->wa_lock, wa_lock_flags); - generic_handle_irq(irq_find_mapping(bank->chip.irq.domain, bit)); - raw_spin_unlock_irqrestore(&bank->wa_lock, wa_lock_flags); + raw_spinlock_t wa_lock; + static irqreturn_t omap_gpio_irq_handler(int irq, void *gpiobank) + unsigned long wa_lock_flags; + raw_spin_lock_irqsave(&bank->wa_lock, wa_lock_flags); + generic_handle_irq(irq_find_mapping(bank->chip.irq.domain, bit)); + raw_spin_unlock_irqrestore(&bank->wa_lock, wa_lock_flags); - GENERIC CHAINED GPIO IRQCHIPS: these are the same as "CHAINED GPIO irqchips", but chained IRQ handlers are not used. Instead GPIO IRQs dispatching is @@ -416,30 +416,69 @@ The preferred way to set up the helpers is to fill in the struct gpio_irq_chip inside struct gpio_chip before adding the gpio_chip. If you do this, the additional irq_chip will be set up by gpiolib at the same time as setting up the rest of the GPIO functionality. The following -is a typical example of a cascaded interrupt handler using gpio_irq_chip:: +is a typical example of a chained cascaded interrupt handler using +the gpio_irq_chip. Note how the mask/unmask (or disable/enable) functions +call into the core gpiolib code: .. code-block:: c - /* Typical state container with dynamic irqchip */ + /* Typical state container */ struct my_gpio { struct gpio_chip gc; - struct irq_chip irq; + }; + + static void my_gpio_mask_irq(struct irq_data *d) + { + struct gpio_chip *gc = irq_data_get_irq_chip_data(d); + irq_hw_number_t hwirq = irqd_to_hwirq(d); + + /* + * Perform any necessary action to mask the interrupt, + * and then call into the core code to synchronise the + * state. + */ + + gpiochip_disable_irq(gc, hwirq); + } + + static void my_gpio_unmask_irq(struct irq_data *d) + { + struct gpio_chip *gc = irq_data_get_irq_chip_data(d); + irq_hw_number_t hwirq = irqd_to_hwirq(d); + + gpiochip_enable_irq(gc, hwirq); + + /* + * Perform any necessary action to unmask the interrupt, + * after having called into the core code to synchronise + * the state. + */ + } + + /* + * Statically populate the irqchip. Note that it is made const + * (further indicated by the IRQCHIP_IMMUTABLE flag), and that + * the GPIOCHIP_IRQ_RESOURCE_HELPER macro adds some extra + * callbacks to the structure. + */ + static const struct irq_chip my_gpio_irq_chip = { + .name = "my_gpio_irq", + .irq_ack = my_gpio_ack_irq, + .irq_mask = my_gpio_mask_irq, + .irq_unmask = my_gpio_unmask_irq, + .irq_set_type = my_gpio_set_irq_type, + .flags = IRQCHIP_IMMUTABLE, + /* Provide the gpio resource callbacks */ + GPIOCHIP_IRQ_RESOURCE_HELPERS, }; int irq; /* from platform etc */ struct my_gpio *g; struct gpio_irq_chip *girq; - /* Set up the irqchip dynamically */ - g->irq.name = "my_gpio_irq"; - g->irq.irq_ack = my_gpio_ack_irq; - g->irq.irq_mask = my_gpio_mask_irq; - g->irq.irq_unmask = my_gpio_unmask_irq; - g->irq.irq_set_type = my_gpio_set_irq_type; - /* Get a pointer to the gpio_irq_chip */ girq = &g->gc.irq; - girq->chip = &g->irq; + gpio_irq_chip_set_chip(girq, &my_gpio_irq_chip); girq->parent_handler = ftgpio_gpio_irq_handler; girq->num_parents = 1; girq->parents = devm_kcalloc(dev, 1, sizeof(*girq->parents), @@ -452,32 +491,147 @@ is a typical example of a cascaded interrupt handler using gpio_irq_chip:: return devm_gpiochip_add_data(dev, &g->gc, g); -The helper support using hierarchical interrupt controllers as well. -In this case the typical set-up will look like this:: +The helper supports using threaded interrupts as well. Then you just request +the interrupt separately and go with it: .. code-block:: c - /* Typical state container with dynamic irqchip */ + /* Typical state container */ struct my_gpio { struct gpio_chip gc; - struct irq_chip irq; - struct fwnode_handle *fwnode; + }; + + static void my_gpio_mask_irq(struct irq_data *d) + { + struct gpio_chip *gc = irq_data_get_irq_chip_data(d); + irq_hw_number_t hwirq = irqd_to_hwirq(d); + + /* + * Perform any necessary action to mask the interrupt, + * and then call into the core code to synchronise the + * state. + */ + + gpiochip_disable_irq(gc, hwirq); + } + + static void my_gpio_unmask_irq(struct irq_data *d) + { + struct gpio_chip *gc = irq_data_get_irq_chip_data(d); + irq_hw_number_t hwirq = irqd_to_hwirq(d); + + gpiochip_enable_irq(gc, hwirq); + + /* + * Perform any necessary action to unmask the interrupt, + * after having called into the core code to synchronise + * the state. + */ + } + + /* + * Statically populate the irqchip. Note that it is made const + * (further indicated by the IRQCHIP_IMMUTABLE flag), and that + * the GPIOCHIP_IRQ_RESOURCE_HELPER macro adds some extra + * callbacks to the structure. + */ + static const struct irq_chip my_gpio_irq_chip = { + .name = "my_gpio_irq", + .irq_ack = my_gpio_ack_irq, + .irq_mask = my_gpio_mask_irq, + .irq_unmask = my_gpio_unmask_irq, + .irq_set_type = my_gpio_set_irq_type, + .flags = IRQCHIP_IMMUTABLE, + /* Provide the gpio resource callbacks */ + GPIOCHIP_IRQ_RESOURCE_HELPERS, }; int irq; /* from platform etc */ struct my_gpio *g; struct gpio_irq_chip *girq; - /* Set up the irqchip dynamically */ - g->irq.name = "my_gpio_irq"; - g->irq.irq_ack = my_gpio_ack_irq; - g->irq.irq_mask = my_gpio_mask_irq; - g->irq.irq_unmask = my_gpio_unmask_irq; - g->irq.irq_set_type = my_gpio_set_irq_type; + ret = devm_request_threaded_irq(dev, irq, NULL, + irq_thread_fn, IRQF_ONESHOT, "my-chip", g); + if (ret < 0) + return ret; + + /* Get a pointer to the gpio_irq_chip */ + girq = &g->gc.irq; + gpio_irq_chip_set_chip(girq, &my_gpio_irq_chip); + /* This will let us handle the parent IRQ in the driver */ + girq->parent_handler = NULL; + girq->num_parents = 0; + girq->parents = NULL; + girq->default_type = IRQ_TYPE_NONE; + girq->handler = handle_bad_irq; + + return devm_gpiochip_add_data(dev, &g->gc, g); + +The helper supports using hierarchical interrupt controllers as well. +In this case the typical set-up will look like this: + +.. code-block:: c + + /* Typical state container with dynamic irqchip */ + struct my_gpio { + struct gpio_chip gc; + struct fwnode_handle *fwnode; + }; + + static void my_gpio_mask_irq(struct irq_data *d) + { + struct gpio_chip *gc = irq_data_get_irq_chip_data(d); + irq_hw_number_t hwirq = irqd_to_hwirq(d); + + /* + * Perform any necessary action to mask the interrupt, + * and then call into the core code to synchronise the + * state. + */ + + gpiochip_disable_irq(gc, hwirq); + irq_mask_mask_parent(d); + } + + static void my_gpio_unmask_irq(struct irq_data *d) + { + struct gpio_chip *gc = irq_data_get_irq_chip_data(d); + irq_hw_number_t hwirq = irqd_to_hwirq(d); + + gpiochip_enable_irq(gc, hwirq); + + /* + * Perform any necessary action to unmask the interrupt, + * after having called into the core code to synchronise + * the state. + */ + + irq_mask_unmask_parent(d); + } + + /* + * Statically populate the irqchip. Note that it is made const + * (further indicated by the IRQCHIP_IMMUTABLE flag), and that + * the GPIOCHIP_IRQ_RESOURCE_HELPER macro adds some extra + * callbacks to the structure. + */ + static const struct irq_chip my_gpio_irq_chip = { + .name = "my_gpio_irq", + .irq_ack = my_gpio_ack_irq, + .irq_mask = my_gpio_mask_irq, + .irq_unmask = my_gpio_unmask_irq, + .irq_set_type = my_gpio_set_irq_type, + .flags = IRQCHIP_IMMUTABLE, + /* Provide the gpio resource callbacks */ + GPIOCHIP_IRQ_RESOURCE_HELPERS, + }; + + struct my_gpio *g; + struct gpio_irq_chip *girq; /* Get a pointer to the gpio_irq_chip */ girq = &g->gc.irq; - girq->chip = &g->irq; + gpio_irq_chip_set_chip(girq, &my_gpio_irq_chip); girq->default_type = IRQ_TYPE_NONE; girq->handler = handle_bad_irq; girq->fwnode = g->fwnode; @@ -488,42 +642,18 @@ In this case the typical set-up will look like this:: As you can see pretty similar, but you do not supply a parent handler for the IRQ, instead a parent irqdomain, an fwnode for the hardware and -a funcion .child_to_parent_hwirq() that has the purpose of looking up +a function .child_to_parent_hwirq() that has the purpose of looking up the parent hardware irq from a child (i.e. this gpio chip) hardware irq. As always it is good to look at examples in the kernel tree for advice on how to find the required pieces. -The old way of adding irqchips to gpiochips after registration is also still -available but we try to move away from this: - -- DEPRECATED: gpiochip_irqchip_add(): adds a chained cascaded irqchip to a - gpiochip. It will pass the struct gpio_chip* for the chip to all IRQ - callbacks, so the callbacks need to embed the gpio_chip in its state - container and obtain a pointer to the container using container_of(). - (See Documentation/driver-api/driver-model/design-patterns.rst) - -- gpiochip_irqchip_add_nested(): adds a nested cascaded irqchip to a gpiochip, - as discussed above regarding different types of cascaded irqchips. The - cascaded irq has to be handled by a threaded interrupt handler. - Apart from that it works exactly like the chained irqchip. - -- DEPRECATED: gpiochip_set_chained_irqchip(): sets up a chained cascaded irq - handler for a gpio_chip from a parent IRQ and passes the struct gpio_chip* - as handler data. Notice that we pass is as the handler data, since the - irqchip data is likely used by the parent irqchip. - -- gpiochip_set_nested_irqchip(): sets up a nested cascaded irq handler for a - gpio_chip from a parent IRQ. As the parent IRQ has usually been - explicitly requested by the driver, this does very little more than - mark all the child IRQs as having the other IRQ as parent. - If there is a need to exclude certain GPIO lines from the IRQ domain handled by these helpers, we can set .irq.need_valid_mask of the gpiochip before devm_gpiochip_add_data() or gpiochip_add_data() is called. This allocates an .irq.valid_mask with as many bits set as there are GPIO lines in the chip, each bit representing line 0..n-1. Drivers can exclude GPIO lines by clearing bits -from this mask. The mask must be filled in before gpiochip_irqchip_add() or -gpiochip_irqchip_add_nested() is called. +from this mask. The mask can be filled in the init_valid_mask() callback +that is part of the struct gpio_irq_chip. To use the helpers please keep the following in mind: @@ -531,13 +661,10 @@ To use the helpers please keep the following in mind: the irqchip can initialize. E.g. .dev and .can_sleep shall be set up properly. -- Nominally set all handlers to handle_bad_irq() in the setup call and pass - handle_bad_irq() as flow handler parameter in gpiochip_irqchip_add() if it is - expected for GPIO driver that irqchip .set_type() callback will be called - before using/enabling each GPIO IRQ. Then set the handler to - handle_level_irq() and/or handle_edge_irq() in the irqchip .set_type() - callback depending on what your controller supports and what is requested - by the consumer. +- Nominally set gpio_irq_chip.handler to handle_bad_irq. Then, if your irqchip + is cascaded, set the handler to handle_level_irq() and/or handle_edge_irq() + in the irqchip .set_type() callback depending on what your controller + supports and what is requested by the consumer. Locking IRQ usage @@ -592,8 +719,9 @@ 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 irqchip. -When using the gpiolib irqchip helpers, these callbacks are automatically -assigned. +When IRQCHIP_IMMUTABLE is not advertised by the irqchip, these callbacks +are automatically assigned. This behaviour is deprecated and on its way +to be removed from the kernel. Real-Time compliance for GPIO IRQ chips @@ -624,8 +752,8 @@ compliance: level and edge IRQs * [1] http://www.spinics.net/lists/linux-omap/msg120425.html -* [2] https://lkml.org/lkml/2015/9/25/494 -* [3] https://lkml.org/lkml/2015/9/25/495 +* [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 Requesting self-owned GPIO pins diff --git a/Documentation/driver-api/gpio/drivers-on-gpio.rst b/Documentation/driver-api/gpio/drivers-on-gpio.rst index f3a189320e11..af632d764ac6 100644 --- a/Documentation/driver-api/gpio/drivers-on-gpio.rst +++ b/Documentation/driver-api/gpio/drivers-on-gpio.rst @@ -89,13 +89,26 @@ hardware descriptions such as device tree or ACPI: Consumer Electronics Control bus using only GPIO. It is used to communicate with devices on the HDMI bus. +- gpio-charger: drivers/power/supply/gpio-charger.c is used if you need to do + battery charging and all you have to go by to check the presence of the + AC charger or more complex tasks such as indicating charging status using + nothing but GPIO lines, this driver provides that and also a clearly defined + way to pass the charging parameters from hardware descriptions such as the + device tree. + +- gpio-mux: drivers/mux/gpio.c is used for controlling a multiplexer using + n GPIO lines such that you can mux in 2^n different devices by activating + different GPIO lines. Often the GPIOs are on a SoC and the devices are + some SoC-external entities, such as different components on a PCB that + can be selectively enabled. + Apart from this there are special GPIO drivers in subsystems like MMC/SD to read card detect and write protect GPIO lines, and in the TTY serial subsystem to emulate MCTRL (modem control) signals CTS/RTS by using two GPIO lines. The MTD NOR flash has add-ons for extra GPIO lines too, though the address bus is usually connected directly to the flash. -Use those instead of talking directly to the GPIOs using sysfs; they integrate -with kernel frameworks better than your userspace code could. Needless to say, -just using the appropriate kernel drivers will simplify and speed up your -embedded hacking in particular by providing ready-made components. +Use those instead of talking directly to the GPIOs from userspace; they +integrate with kernel frameworks better than your userspace code could. +Needless to say, just using the appropriate kernel drivers will simplify and +speed up your embedded hacking in particular by providing ready-made components. diff --git a/Documentation/driver-api/gpio/index.rst b/Documentation/driver-api/gpio/index.rst index 5b61032aa4ea..1d48fe248f05 100644 --- a/Documentation/driver-api/gpio/index.rst +++ b/Documentation/driver-api/gpio/index.rst @@ -8,6 +8,7 @@ Contents: :maxdepth: 2 intro + using-gpio driver consumer board diff --git a/Documentation/driver-api/gpio/intro.rst b/Documentation/driver-api/gpio/intro.rst index 74591489d0b5..c9c19243b97f 100644 --- a/Documentation/driver-api/gpio/intro.rst +++ b/Documentation/driver-api/gpio/intro.rst @@ -14,12 +14,12 @@ Due to the history of GPIO interfaces in the kernel, there are two different ways to obtain and use GPIOs: - The descriptor-based interface is the preferred way to manipulate GPIOs, - and is described by all the files in this directory excepted gpio-legacy.txt. + and is described by all the files in this directory excepted legacy.rst. - The legacy integer-based interface which is considered deprecated (but still - usable for compatibility reasons) is documented in gpio-legacy.txt. + usable for compatibility reasons) is documented in legacy.rst. The remainder of this document applies to the new descriptor-based interface. -gpio-legacy.txt contains the same information applied to the legacy +legacy.rst contains the same information applied to the legacy integer-based interface. @@ -27,7 +27,7 @@ What is a GPIO? =============== A "General Purpose Input/Output" (GPIO) is a flexible software-controlled -digital signal. They are provided from many kinds of chip, and are familiar +digital signal. They are provided from many kinds of chips, and are familiar to Linux developers working with embedded and custom hardware. Each GPIO represents a bit connected to a particular pin, or "ball" on Ball Grid Array (BGA) packages. Board schematics show which external hardware connects to @@ -106,11 +106,11 @@ don't. When you need open drain signaling but your hardware doesn't directly support it, there's a common idiom you can use to emulate it with any GPIO pin that can be used as either an input or an output: - LOW: gpiod_direction_output(gpio, 0) ... this drives the signal and overrides - the pullup. + **LOW**: ``gpiod_direction_output(gpio, 0)`` ... this drives the signal and + overrides the pullup. - HIGH: gpiod_direction_input(gpio) ... this turns off the output, so the pullup - (or some other device) controls the signal. + **HIGH**: ``gpiod_direction_input(gpio)`` ... this turns off the output, so + the pullup (or some other device) controls the signal. The same logic can be applied to emulate open source signaling, by driving the high signal and configuring the GPIO as input for low. This open drain/open diff --git a/Documentation/driver-api/gpio/legacy.rst b/Documentation/driver-api/gpio/legacy.rst index 9bc34ba697d9..b6505914791c 100644 --- a/Documentation/driver-api/gpio/legacy.rst +++ b/Documentation/driver-api/gpio/legacy.rst @@ -165,8 +165,7 @@ Most GPIO controllers can be accessed with memory read/write instructions. Those don't need to sleep, and can safely be done from inside hard (nonthreaded) IRQ handlers and similar contexts. -Use the following calls to access such GPIOs, -for which gpio_cansleep() will always return false (see below):: +Use the following calls to access such GPIOs:: /* GPIO INPUT: return zero or nonzero */ int gpio_get_value(unsigned gpio); @@ -200,13 +199,6 @@ Some GPIO controllers must be accessed using message based busses like I2C or SPI. Commands to read or write those GPIO values require waiting to get to the head of a queue to transmit a command and get its response. This requires sleeping, which can't be done from inside IRQ handlers. - -Platforms that support this type of GPIO distinguish them from other GPIOs -by returning nonzero from this call (which requires a valid GPIO number, -which should have been previously allocated with gpio_request):: - - int gpio_cansleep(unsigned gpio); - To access such GPIOs, a different set of accessors is defined:: /* GPIO INPUT: return zero or nonzero, might sleep */ @@ -215,7 +207,6 @@ To access such GPIOs, a different set of accessors is defined:: /* GPIO OUTPUT, might sleep */ void gpio_set_value_cansleep(unsigned gpio, int value); - Accessing such GPIOs requires a context which may sleep, for example a threaded IRQ handler, and those accessors must be used instead of spinlock-safe accessors without the cansleep() name suffix. @@ -238,8 +229,6 @@ setup or driver probe/teardown code, so this is an easy constraint.):: ## gpio_free_array() gpio_free() - gpio_set_debounce() - Claiming and Releasing GPIOs @@ -321,11 +310,6 @@ where 'flags' is currently defined to specify the following properties: * GPIOF_INIT_LOW - as output, set initial level to LOW * GPIOF_INIT_HIGH - as output, set initial level to HIGH - * GPIOF_OPEN_DRAIN - gpio pin is open drain type. - * GPIOF_OPEN_SOURCE - gpio pin is open source type. - - * GPIOF_EXPORT_DIR_FIXED - export gpio to sysfs, keep direction - * GPIOF_EXPORT_DIR_CHANGEABLE - also export, allow changing direction since GPIOF_INIT_* are only valid when configured as output, so group valid combinations as: @@ -334,20 +318,6 @@ combinations as: * GPIOF_OUT_INIT_LOW - configured as output, initial level LOW * GPIOF_OUT_INIT_HIGH - configured as output, initial level HIGH -When setting the flag as GPIOF_OPEN_DRAIN then it will assume that pins is -open drain type. Such pins will not be driven to 1 in output mode. It is -require to connect pull-up on such pins. By enabling this flag, gpio lib will -make the direction to input when it is asked to set value of 1 in output mode -to make the pin HIGH. The pin is make to LOW by driving value 0 in output mode. - -When setting the flag as GPIOF_OPEN_SOURCE then it will assume that pins is -open source type. Such pins will not be driven to 0 in output mode. It is -require to connect pull-down on such pin. By enabling this flag, gpio lib will -make the direction to input when it is asked to set value of 0 in output mode -to make the pin LOW. The pin is make to HIGH by driving value 1 in output mode. - -In the future, these flags can be extended to support more properties. - Further more, to ease the claim/release of multiple GPIOs, 'struct gpio' is introduced to encapsulate all three fields as:: @@ -387,9 +357,6 @@ map between them using calls like:: /* map GPIO numbers to IRQ numbers */ int gpio_to_irq(unsigned gpio); - /* map IRQ numbers to GPIO numbers (avoid using this) */ - int irq_to_gpio(unsigned irq); - Those return either the corresponding number in the other namespace, or else a negative errno code if the mapping can't be done. (For example, some GPIOs can't be used as IRQs.) It is an unchecked error to use a GPIO @@ -405,11 +372,6 @@ devices, by the board-specific initialization code. Note that IRQ trigger options are part of the IRQ interface, e.g. IRQF_TRIGGER_FALLING, as are system wakeup capabilities. -Non-error values returned from irq_to_gpio() would most commonly be used -with gpio_get_value(), for example to initialize or update driver state -when the IRQ is edge-triggered. Note that some platforms don't support -this reverse mapping, so you should avoid using it. - Emulating Open Drain Signals ---------------------------- @@ -461,7 +423,7 @@ pin controller? This is done by registering "ranges" of pins, which are essentially cross-reference tables. These are described in -Documentation/driver-api/pinctl.rst +Documentation/driver-api/pin-control.rst While the pin allocation is totally managed by the pinctrl subsystem, gpio (under gpiolib) is still maintained by gpio drivers. It may happen @@ -558,11 +520,6 @@ Platform Support To force-enable this framework, a platform's Kconfig will "select" GPIOLIB, else it is up to the user to configure support for GPIO. -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. - If neither of these options are selected, the platform does not support GPIOs through GPIO-lib and the code cannot be enabled by the user. @@ -571,7 +528,6 @@ code, which always dispatches through the gpio_chip:: #define gpio_get_value __gpio_get_value #define gpio_set_value __gpio_set_value - #define gpio_cansleep __gpio_cansleep Fancier implementations could instead define those as inline functions with logic optimizing access to specific SOC-based GPIOs. For example, if the @@ -729,36 +685,6 @@ gpiochip nodes (possibly in conjunction with schematics) to determine the correct GPIO number to use for a given signal. -Exporting from Kernel code --------------------------- -Kernel code can explicitly manage exports of GPIOs which have already been -requested using gpio_request():: - - /* export the GPIO to userspace */ - int gpio_export(unsigned gpio, bool direction_may_change); - - /* reverse gpio_export() */ - void gpio_unexport(); - - /* create a sysfs link to an exported GPIO node */ - int gpio_export_link(struct device *dev, const char *name, - unsigned gpio) - -After a kernel driver requests a GPIO, it may only be made available in -the sysfs interface by gpio_export(). The driver can control whether the -signal direction may change. This helps drivers prevent userspace code -from accidentally clobbering important system state. - -This explicit exporting can help with debugging (by making some kinds -of experiments easier), or can provide an always-there interface that's -suitable for documenting as part of a board support package. - -After the GPIO has been exported, gpio_export_link() allows creating -symlinks from elsewhere in sysfs to the GPIO sysfs node. Drivers can -use this to provide the interface under their own device in sysfs with -a descriptive name. - - API Reference ============= diff --git a/Documentation/driver-api/gpio/using-gpio.rst b/Documentation/driver-api/gpio/using-gpio.rst new file mode 100644 index 000000000000..894d88855d73 --- /dev/null +++ b/Documentation/driver-api/gpio/using-gpio.rst @@ -0,0 +1,50 @@ +========================= +Using GPIO Lines in Linux +========================= + +The Linux kernel exists to abstract and present hardware to users. GPIO lines +as such are normally not user facing abstractions. The most obvious, natural +and preferred way to use GPIO lines is to let kernel hardware drivers deal +with them. + +For examples of already existing generic drivers that will also be good +examples for any other kernel drivers you want to author, refer to +Documentation/driver-api/gpio/drivers-on-gpio.rst + +For any kind of mass produced system you want to support, such as servers, +laptops, phones, tablets, routers, and any consumer or office or business goods +using appropriate kernel drivers is paramount. Submit your code for inclusion +in the upstream Linux kernel when you feel it is mature enough and you will get +help to refine it, see Documentation/process/submitting-patches.rst. + +In Linux GPIO lines also have a userspace ABI. + +The userspace ABI is intended for one-off deployments. Examples are prototypes, +factory lines, maker community projects, workshop specimen, production tools, +industrial automation, PLC-type use cases, door controllers, in short a piece +of specialized equipment that is not produced by the numbers, requiring +operators to have a deep knowledge of the equipment and knows about the +software-hardware interface to be set up. They should not have a natural fit +to any existing kernel subsystem and not be a good fit for an operating system, +because of not being reusable or abstract enough, or involving a lot of non +computer hardware related policy. + +Applications that have a good reason to use the industrial I/O (IIO) subsystem +from userspace will likely be a good fit for using GPIO lines from userspace as +well. + +Do not under any circumstances abuse the GPIO userspace ABI to cut corners in +any product development projects. If you use it for prototyping, then do not +productify the prototype: rewrite it using proper kernel drivers. Do not under +any circumstances deploy any uniform products using GPIO from userspace. + +The userspace ABI is a character device for each GPIO hardware unit (GPIO chip). +These devices will appear on the system as ``/dev/gpiochip0`` thru +``/dev/gpiochipN``. Examples of how to directly use the userspace ABI can be +found in the kernel tree ``tools/gpio`` subdirectory. + +For structured and managed applications, we recommend that you make use of the +libgpiod_ library. This provides helper abstractions, command line utilities +and arbitration for multiple simultaneous consumers on the same GPIO chip. + +.. _libgpiod: https://git.kernel.org/pub/scm/libs/libgpiod/libgpiod.git/ |