diff options
Diffstat (limited to 'kernel/Documentation/gpio')
| -rw-r--r-- | kernel/Documentation/gpio/00-INDEX | 3 | ||||
| -rw-r--r-- | kernel/Documentation/gpio/board.txt | 38 | ||||
| -rw-r--r-- | kernel/Documentation/gpio/consumer.txt | 66 | ||||
| -rw-r--r-- | kernel/Documentation/gpio/driver.txt | 80 | ||||
| -rw-r--r-- | kernel/Documentation/gpio/drivers-on-gpio.txt | 95 | ||||
| -rw-r--r-- | kernel/Documentation/gpio/gpio-legacy.txt | 9 | ||||
| -rw-r--r-- | kernel/Documentation/gpio/sysfs.txt | 21 |
7 files changed, 261 insertions, 51 deletions
diff --git a/kernel/Documentation/gpio/00-INDEX b/kernel/Documentation/gpio/00-INDEX index 1de43ae46..179beb234 100644 --- a/kernel/Documentation/gpio/00-INDEX +++ b/kernel/Documentation/gpio/00-INDEX @@ -6,6 +6,9 @@ consumer.txt - How to obtain and use GPIOs in a driver driver.txt - How to write a GPIO driver +drivers-on-gpio.txt: + - Drivers in other subsystems that can use GPIO to provide more + complex functionality. board.txt - How to assign GPIOs to a consumer device and a function sysfs.txt diff --git a/kernel/Documentation/gpio/board.txt b/kernel/Documentation/gpio/board.txt index b80606de5..309217862 100644 --- a/kernel/Documentation/gpio/board.txt +++ b/kernel/Documentation/gpio/board.txt @@ -34,20 +34,33 @@ through gpiod_get(). For example: power-gpios = <&gpio 1 GPIO_ACTIVE_LOW>; }; +Properties named <function>-gpio are also considered valid and old bindings use +it but are only supported for compatibility reasons and should not be used for +newer bindings since it has been deprecated. + This property will make GPIOs 15, 16 and 17 available to the driver under the "led" function, and GPIO 1 as the "power" GPIO: struct gpio_desc *red, *green, *blue, *power; - red = gpiod_get_index(dev, "led", 0); - green = gpiod_get_index(dev, "led", 1); - blue = gpiod_get_index(dev, "led", 2); + red = gpiod_get_index(dev, "led", 0, GPIOD_OUT_HIGH); + green = gpiod_get_index(dev, "led", 1, GPIOD_OUT_HIGH); + blue = gpiod_get_index(dev, "led", 2, GPIOD_OUT_HIGH); - power = gpiod_get(dev, "power"); + power = gpiod_get(dev, "power", GPIOD_OUT_HIGH); The led GPIOs will be active-high, while the power GPIO will be active-low (i.e. gpiod_is_active_low(power) will be true). +The second parameter of the gpiod_get() functions, the con_id string, has to be +the <function>-prefix of the GPIO suffixes ("gpios" or "gpio", automatically +looked up by the gpiod functions internally) used in the device tree. With above +"led-gpios" example, use the prefix without the "-" as con_id parameter: "led". + +Internally, the GPIO subsystem prefixes the GPIO suffix ("gpios" or "gpio") +with the string passed in con_id to get the resulting string +(snprintf(... "%s-%s", con_id, gpio_suffixes[]). + ACPI ---- ACPI also supports function names for GPIOs in a similar fashion to DT. @@ -142,13 +155,14 @@ The driver controlling "foo.0" will then be able to obtain its GPIOs as follows: struct gpio_desc *red, *green, *blue, *power; - red = gpiod_get_index(dev, "led", 0); - green = gpiod_get_index(dev, "led", 1); - blue = gpiod_get_index(dev, "led", 2); + red = gpiod_get_index(dev, "led", 0, GPIOD_OUT_HIGH); + green = gpiod_get_index(dev, "led", 1, GPIOD_OUT_HIGH); + blue = gpiod_get_index(dev, "led", 2, GPIOD_OUT_HIGH); - power = gpiod_get(dev, "power"); - gpiod_direction_output(power, 1); + power = gpiod_get(dev, "power", GPIOD_OUT_HIGH); -Since the "power" GPIO is mapped as active-low, its actual signal will be 0 -after this code. Contrary to the legacy integer GPIO interface, the active-low -property is handled during mapping and is thus transparent to GPIO consumers. +Since the "led" GPIOs are mapped as active-high, this example will switch their +signals to 1, i.e. enabling the LEDs. And for the "power" GPIO, which is mapped +as active-low, its actual signal will be 0 after this code. Contrary to the legacy +integer GPIO interface, the active-low property is handled during mapping and is +thus transparent to GPIO consumers. diff --git a/kernel/Documentation/gpio/consumer.txt b/kernel/Documentation/gpio/consumer.txt index c21c1313f..e000502fd 100644 --- a/kernel/Documentation/gpio/consumer.txt +++ b/kernel/Documentation/gpio/consumer.txt @@ -39,6 +39,9 @@ device that displays digits), an additional index argument can be specified: const char *con_id, unsigned int idx, enum gpiod_flags flags) +For a more detailed description of the con_id parameter in the DeviceTree case +see Documentation/gpio/board.txt + The flags parameter is used to optionally specify a direction and initial value for the GPIO. Values can be: @@ -237,22 +240,55 @@ Note that these functions should only be used with great moderation ; a driver should not have to care about the physical line level. +The active-low property +----------------------- + +As a driver should not have to care about the physical line level, all of the +gpiod_set_value_xxx() or gpiod_set_array_value_xxx() functions operate with +the *logical* value. With this they take the active-low property into account. +This means that they check whether the GPIO is configured to be active-low, +and if so, they manipulate the passed value before the physical line level is +driven. + +With this, all the gpiod_set_(array)_value_xxx() functions interpret the +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 "active" ("1"), the physical line level +will be driven low. + +To summarize: + +Function (example) active-low proporty physical line +gpiod_set_raw_value(desc, 0); don't care low +gpiod_set_raw_value(desc, 1); don't care high +gpiod_set_value(desc, 0); default (active-high) low +gpiod_set_value(desc, 1); default (active-high) high +gpiod_set_value(desc, 0); active-low high +gpiod_set_value(desc, 1); active-low low + +Please note again that the set_raw/get_raw functions should be avoided as much +as possible, especially by drivers which should not care about the actual +physical line level and worry about the logical value instead. + + Set multiple GPIO outputs with a single function call ----------------------------------------------------- The following functions set the output values of an array of GPIOs: - void gpiod_set_array(unsigned int array_size, - struct gpio_desc **desc_array, - int *value_array) - void gpiod_set_raw_array(unsigned int array_size, - struct gpio_desc **desc_array, - int *value_array) - void gpiod_set_array_cansleep(unsigned int array_size, - struct gpio_desc **desc_array, - int *value_array) - void gpiod_set_raw_array_cansleep(unsigned int array_size, - struct gpio_desc **desc_array, - int *value_array) + void gpiod_set_array_value(unsigned int array_size, + struct gpio_desc **desc_array, + int *value_array) + void gpiod_set_raw_array_value(unsigned int array_size, + struct gpio_desc **desc_array, + int *value_array) + void gpiod_set_array_value_cansleep(unsigned int array_size, + struct gpio_desc **desc_array, + int *value_array) + void gpiod_set_raw_array_value_cansleep(unsigned int array_size, + struct gpio_desc **desc_array, + int *value_array) The array can be an arbitrary set of GPIOs. The functions will try to set GPIOs belonging to the same bank or chip simultaneously if supported by the @@ -271,8 +307,8 @@ matches the desired group of GPIOs, those GPIOs can be set by simply using the struct gpio_descs returned by gpiod_get_array(): struct gpio_descs *my_gpio_descs = gpiod_get_array(...); - gpiod_set_array(my_gpio_descs->ndescs, my_gpio_descs->desc, - my_gpio_values); + gpiod_set_array_value(my_gpio_descs->ndescs, my_gpio_descs->desc, + my_gpio_values); It is also possible to set a completely arbitrary array of descriptors. The descriptors may be obtained using any combination of gpiod_get() and @@ -290,7 +326,7 @@ corresponding to a given GPIO using the following call: int gpiod_to_irq(const struct gpio_desc *desc) -It will return an IRQ number, or an negative errno code if the mapping can't be +It will return an IRQ number, or a negative errno code if the mapping can't be done (most likely because that particular GPIO cannot be used as IRQ). It is an unchecked error to use a GPIO that wasn't set up as an input using gpiod_direction_input(), or to use an IRQ number that didn't originally come diff --git a/kernel/Documentation/gpio/driver.txt b/kernel/Documentation/gpio/driver.txt index 90d0f6aba..12a61948e 100644 --- a/kernel/Documentation/gpio/driver.txt +++ b/kernel/Documentation/gpio/driver.txt @@ -62,6 +62,11 @@ Any debugfs dump method should normally ignore signals which haven't been requested as GPIOs. They can use gpiochip_is_requested(), which returns either NULL or the label associated with that GPIO when it was requested. +RT_FULL: GPIO driver should not use spinlock_t or any sleepable APIs +(like PM runtime) in its gpio_chip implementation (.get/.set and direction +control callbacks) if it is expected to call GPIO APIs from atomic context +on -RT (inside hard IRQ handlers and similar contexts). Normally this should +not be required. GPIO drivers providing IRQs --------------------------- @@ -73,6 +78,13 @@ The IRQ portions of the GPIO block are implemented using an irqchip, using the header <linux/irq.h>. So basically such a driver is utilizing two sub- systems simultaneously: gpio and irq. +RT_FULL: GPIO driver should not use spinlock_t or any sleepable APIs +(like PM runtime) as part of its irq_chip implementation on -RT. +- spinlock_t should be replaced with raw_spinlock_t [1]. +- If sleepable APIs have to be used, these can be done from the .irq_bus_lock() + and .irq_bus_unlock() callbacks, as these are the only slowpath callbacks + on an irqchip. Create the callbacks if needed [2]. + GPIO irqchips usually fall in one of two categories: * CHAINED GPIO irqchips: these are usually the type that is embedded on @@ -93,6 +105,38 @@ GPIO irqchips usually fall in one of two categories: Chained GPIO irqchips typically can NOT set the .can_sleep flag on struct gpio_chip, as everything happens directly in the callbacks. + RT_FULL: Note, chained IRQ handlers will not be forced threaded on -RT. + As result, spinlock_t or any sleepable APIs (like PM runtime) can't be used + in chained IRQ handler. + if required (and if it can't be converted to the nested threaded GPIO irqchip) + - chained IRQ handler can be converted to generic irq handler and this way + it will be threaded IRQ handler on -RT and hard IRQ handler on non-RT + (for example, see [3]). + Know W/A: The generic_handle_irq() is expected to be called with IRQ disabled, + so IRQ core will complain if it will be called from IRQ handler wich is forced + thread. The "fake?" raw lock can be used to W/A 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.irqdomain, 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 + performed by generic IRQ handler which is configured using request_irq(). + The GPIO irqchip will then end up calling something like this sequence in + its interrupt handler: + + static irqreturn_t gpio_rcar_irq_handler(int irq, void *dev_id) + for each detected GPIO IRQ + generic_handle_irq(...); + + RT_FULL: Such kind of handlers will be forced threaded on -RT, as result IRQ + core will complain that generic_handle_irq() is called with IRQ enabled and + the same W/A as for "CHAINED GPIO irqchips" can be applied. + * NESTED THREADED GPIO irqchips: these are off-chip GPIO expanders and any other GPIO irqchip residing on the other side of a sleeping bus. Of course such drivers that need slow bus traffic to read out IRQ status and similar, @@ -133,6 +177,13 @@ 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 have to be called + before using/enabling 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. + It is legal for any IRQ consumer to request an IRQ from any irqchip no matter if that is a combined GPIO+IRQ driver. The basic premise is that gpio_chip and irq_chip are orthogonal, and offering their services independent of each @@ -169,6 +220,31 @@ When implementing an irqchip inside a GPIO driver, these two functions should typically be called in the .startup() and .shutdown() callbacks from the irqchip. +Real-Time compliance for GPIO IRQ chips +--------------------------------------- + +Any provider of irqchips needs to be carefully tailored to support Real Time +preemption. It is desireable that all irqchips in the GPIO subsystem keep this +in mind and does the proper testing to assure they are real time-enabled. +So, pay attention on above " RT_FULL:" notes, please. +The following is a checklist to follow when preparing a driver for real +time-compliance: + +- ensure spinlock_t is not used as part irq_chip implementation; +- ensure that sleepable APIs are not used as part irq_chip implementation. + If sleepable APIs have to be used, these can be done from the .irq_bus_lock() + and .irq_bus_unlock() callbacks; +- Chained GPIO irqchips: ensure spinlock_t or any sleepable APIs are not used + from chained IRQ handler; +- Generic chained GPIO irqchips: take care about generic_handle_irq() calls and + apply corresponding W/A; +- Chained GPIO irqchips: get rid of chained IRQ handler and use generic irq + handler if possible :) +- regmap_mmio: Sry, but you are in trouble :( if MMIO regmap is used as for + GPIO IRQ chip implementation; +- Test your driver with the appropriate in-kernel real time test cases for both + level and edge IRQs. + Requesting self-owned GPIO pins ------------------------------- @@ -190,3 +266,7 @@ gpiochip_free_own_desc(). These functions must be used with care since they do not affect module use count. Do not use the functions to request gpio descriptors not owned by the calling driver. + +[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 diff --git a/kernel/Documentation/gpio/drivers-on-gpio.txt b/kernel/Documentation/gpio/drivers-on-gpio.txt new file mode 100644 index 000000000..f61213286 --- /dev/null +++ b/kernel/Documentation/gpio/drivers-on-gpio.txt @@ -0,0 +1,95 @@ +Subsystem drivers using GPIO +============================ + +Note that standard kernel drivers exist for common GPIO tasks and will provide +the right in-kernel and userspace APIs/ABIs for the job, and that these +drivers can quite easily interconnect with other kernel subsystems using +hardware descriptions such as device tree or ACPI: + +- leds-gpio: drivers/leds/leds-gpio.c will handle LEDs connected to GPIO + lines, giving you the LED sysfs interface + +- ledtrig-gpio: drivers/leds/trigger/ledtrig-gpio.c will provide a LED trigger, + i.e. a LED will turn on/off in response to a GPIO line going high or low + (and that LED may in turn use the leds-gpio as per above). + +- gpio-keys: drivers/input/keyboard/gpio_keys.c is used when your GPIO line + can generate interrupts in response to a key press. Also supports debounce. + +- gpio-keys-polled: drivers/input/keyboard/gpio_keys_polled.c is used when your + GPIO line cannot generate interrupts, so it needs to be periodically polled + by a timer. + +- gpio_mouse: drivers/input/mouse/gpio_mouse.c is used to provide a mouse with + up to three buttons by simply using GPIOs and no mouse port. You can cut the + mouse cable and connect the wires to GPIO lines or solder a mouse connector + to the lines for a more permanent solution of this type. + +- gpio-beeper: drivers/input/misc/gpio-beeper.c is used to provide a beep from + an external speaker connected to a GPIO line. + +- gpio-tilt-polled: drivers/input/misc/gpio_tilt_polled.c provides tilt + detection switches using GPIO, which is useful for your homebrewn pinball + machine if for nothing else. It can detect different tilt angles of the + monitored object. + +- extcon-gpio: drivers/extcon/extcon-gpio.c is used when you need to read an + external connector status, such as a headset line for an audio driver or an + HDMI connector. It will provide a better userspace sysfs interface than GPIO. + +- restart-gpio: drivers/power/gpio-restart.c is used to restart/reboot the + system by pulling a GPIO line and will register a restart handler so + userspace can issue the right system call to restart the system. + +- poweroff-gpio: drivers/power/gpio-poweroff.c is used to power the system down + by pulling a GPIO line and will register a pm_power_off() callback so that + userspace can issue the right system call to power down the system. + +- gpio-gate-clock: drivers/clk/clk-gpio-gate.c is used to control a gated clock + (off/on) that uses a GPIO, and integrated with the clock subsystem. + +- i2c-gpio: drivers/i2c/busses/i2c-gpio.c is used to drive an I2C bus + (two wires, SDA and SCL lines) by hammering (bitbang) two GPIO lines. It will + appear as any other I2C bus to the system and makes it possible to connect + drivers for the I2C devices on the bus like any other I2C bus driver. + +- spi_gpio: drivers/spi/spi-gpio.c is used to drive an SPI bus (variable number + of wires, atleast SCK and optionally MISO, MOSI and chip select lines) using + GPIO hammering (bitbang). It will appear as any other SPI bus on the system + and makes it possible to connect drivers for SPI devices on the bus like + any other SPI bus driver. For example any MMC/SD card can then be connected + to this SPI by using the mmc_spi host from the MMC/SD card subsystem. + +- w1-gpio: drivers/w1/masters/w1-gpio.c is used to drive a one-wire bus using + a GPIO line, integrating with the W1 subsystem and handling devices on + the bus like any other W1 device. + +- gpio-fan: drivers/hwmon/gpio-fan.c is used to control a fan for cooling the + system, connected to a GPIO line (and optionally a GPIO alarm line), + presenting all the right in-kernel and sysfs interfaces to make your system + not overheat. + +- gpio-regulator: drivers/regulator/gpio-regulator.c is used to control a + regulator providing a certain voltage by pulling a GPIO line, integrating + with the regulator subsystem and giving you all the right interfaces. + +- gpio-wdt: drivers/watchdog/gpio_wdt.c is used to provide a watchdog timer + that will periodically "ping" a hardware connected to a GPIO line by toggling + it from 1-to-0-to-1. If that hardware does not recieve its "ping" + periodically, it will reset the system. + +- gpio-nand: drivers/mtd/nand/gpio.c is used to connect a NAND flash chip to + a set of simple GPIO lines: RDY, NCE, ALE, CLE, NWP. It interacts with the + NAND flash MTD subsystem and provides chip access and partition parsing like + any other NAND driving hardware. + +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 apropriate kernel drivers will simplify and speed up your +embedded hacking in particular by providing ready-made components. diff --git a/kernel/Documentation/gpio/gpio-legacy.txt b/kernel/Documentation/gpio/gpio-legacy.txt index 6f83fa965..79ab5648d 100644 --- a/kernel/Documentation/gpio/gpio-legacy.txt +++ b/kernel/Documentation/gpio/gpio-legacy.txt @@ -751,9 +751,6 @@ requested using gpio_request(): int gpio_export_link(struct device *dev, const char *name, unsigned gpio) - /* change the polarity of a GPIO node in sysfs */ - int gpio_sysfs_set_active_low(unsigned gpio, int value); - 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 @@ -767,9 +764,3 @@ 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. - -Drivers can use gpio_sysfs_set_active_low() to hide GPIO line polarity -differences between boards from user space. This only affects the -sysfs interface. Polarity change can be done both before and after -gpio_export(), and previously enabled poll(2) support for either -rising or falling edge will be reconfigured to follow this setting. diff --git a/kernel/Documentation/gpio/sysfs.txt b/kernel/Documentation/gpio/sysfs.txt index c2c3a97f8..aeab01aa4 100644 --- a/kernel/Documentation/gpio/sysfs.txt +++ b/kernel/Documentation/gpio/sysfs.txt @@ -20,15 +20,14 @@ userspace GPIO can be used to determine system configuration data that standard kernels won't know about. And for some tasks, simple userspace GPIO drivers could be all that the system really needs. -Note that standard kernel drivers exist for common "LEDs and Buttons" -GPIO tasks: "leds-gpio" and "gpio_keys", respectively. Use those -instead of talking directly to the GPIOs; they integrate with kernel -frameworks better than your userspace code could. - +DO NOT ABUSE SYSFS TO CONTROL HARDWARE THAT HAS PROPER KERNEL DRIVERS. +PLEASE READ THE DOCUMENT NAMED "drivers-on-gpio.txt" IN THIS DOCUMENTATION +DIRECTORY TO AVOID REINVENTING KERNEL WHEELS IN USERSPACE. I MEAN IT. +REALLY. Paths in Sysfs -------------- -There are three kinds of entry in /sys/class/gpio: +There are three kinds of entries in /sys/class/gpio: - Control interfaces used to get userspace control over GPIOs; @@ -107,7 +106,7 @@ read-only attributes: "label" ... provided for diagnostics (not always unique) - "ngpio" ... how many GPIOs this manges (N to N + ngpio - 1) + "ngpio" ... how many GPIOs this manages (N to N + ngpio - 1) Board documentation should in most cases cover what GPIOs are used for what purposes. However, those numbers are not always stable; GPIOs on @@ -132,9 +131,6 @@ requested using gpio_request(): int gpiod_export_link(struct device *dev, const char *name, struct gpio_desc *desc); - /* change the polarity of a GPIO node in sysfs */ - int gpiod_sysfs_set_active_low(struct gpio_desc *desc, int value); - After a kernel driver requests a GPIO, it may only be made available in the sysfs interface by gpiod_export(). The driver can control whether the signal direction may change. This helps drivers prevent userspace code @@ -148,8 +144,3 @@ After the GPIO has been exported, gpiod_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. - -Drivers can use gpiod_sysfs_set_active_low() to hide GPIO line polarity -differences between boards from user space. Polarity change can be done both -before and after gpiod_export(), and previously enabled poll(2) support for -either rising or falling edge will be reconfigured to follow this setting. |