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-rw-r--r--Documentation/gpio/driver.txt62
1 files changed, 36 insertions, 26 deletions
diff --git a/Documentation/gpio/driver.txt b/Documentation/gpio/driver.txt
index 368d5a294d89..747c721776ed 100644
--- a/Documentation/gpio/driver.txt
+++ b/Documentation/gpio/driver.txt
@@ -175,8 +175,8 @@ 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.
+RT_FULL: a realtime compliant GPIO driver should not use spinlock_t or any
+sleepable APIs (like PM runtime) as part of its irq_chip implementation.
- 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
@@ -185,33 +185,32 @@ RT_FULL: GPIO driver should not use spinlock_t or any sleepable APIs
GPIO irqchips usually fall in one of two categories:
* CHAINED GPIO irqchips: these are usually the type that is embedded on
- an SoC. This means that there is a fast IRQ handler for the GPIOs that
+ an SoC. This means that there is a fast IRQ flow handler for the GPIOs that
gets called in a chain from the parent IRQ handler, most typically the
- system interrupt controller. This means the GPIO irqchip is registered
- using irq_set_chained_handler() or the corresponding
- gpiochip_set_chained_irqchip() helper function, and the GPIO irqchip
- handler will be called immediately from the parent irqchip, while
- holding the IRQs disabled. The GPIO irqchip will then end up calling
- something like this sequence in its interrupt handler:
-
- static irqreturn_t tc3589x_gpio_irq(int irq, void *data)
+ system interrupt controller. This means that the GPIO irqchip handler will
+ be called immediately from the parent irqchip, while holding the IRQs
+ disabled. The GPIO irqchip will then end up calling something like this
+ sequence in its interrupt handler:
+
+ static irqreturn_t foo_gpio_irq(int irq, void *data)
chained_irq_enter(...);
generic_handle_irq(...);
chained_irq_exit(...);
Chained GPIO irqchips typically can NOT set the .can_sleep flag on
- struct gpio_chip, as everything happens directly in the callbacks.
+ struct gpio_chip, as everything happens directly in the callbacks: no
+ slow bus traffic like I2C can be used.
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
+ If required (and if it can't be converted to the nested threaded GPIO irqchip)
+ a chained IRQ handler can be converted to generic irq handler and this way
+ it will be a threaded IRQ handler on -RT and a 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 which is
- forced thread. The "fake?" raw lock can be used to W/A this problem:
+ so the IRQ core will complain if it is called from an IRQ handler which is
+ forced to a 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)
@@ -243,7 +242,7 @@ GPIO irqchips usually fall in one of two categories:
by the driver. The hallmark of this driver is to call something like
this in its interrupt handler:
- static irqreturn_t tc3589x_gpio_irq(int irq, void *data)
+ static irqreturn_t foo_gpio_irq(int irq, void *data)
...
handle_nested_irq(irq);
@@ -256,23 +255,31 @@ associated irqdomain and resource allocation callbacks, the gpiolib has
some helpers that can be enabled by selecting the GPIOLIB_IRQCHIP Kconfig
symbol:
-* gpiochip_irqchip_add(): adds an irqchip to a gpiochip. It will pass
+* gpiochip_irqchip_add(): adds a chained 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-model/design-patterns.txt)
- If there is a need to exclude certain GPIOs from the IRQ domain, one can
- set .irq_need_valid_mask of the gpiochip before gpiochip_add_data() is
- called. This allocates .irq_valid_mask with as many bits set as there are
- GPIOs in the chip. Drivers can exclude GPIOs by clearing bits from this
- mask. The mask must be filled in before gpiochip_irqchip_add() is called.
+* gpiochip_irqchip_add_nested(): adds a nested irqchip to a gpiochip.
+ Apart from that it works exactly like the chained irqchip.
* gpiochip_set_chained_irqchip(): sets up a chained irq handler for a
gpio_chip from a parent IRQ and passes the struct gpio_chip* as handler
data. (Notice handler data, since the irqchip data is likely used by the
- parent irqchip!) This is for the chained type of chip. This is also used
- to set up a nested irqchip if NULL is passed as handler.
+ parent irqchip!).
+
+* gpiochip_set_nested_irqchip(): sets up a nested 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 GPIOs from the IRQ domain, you can
+set .irq_need_valid_mask of the gpiochip before gpiochip_add_data() is
+called. This allocates an .irq_valid_mask with as many bits set as there
+are GPIOs in the chip. Drivers can exclude GPIOs by clearing bits from this
+mask. The mask must be filled in before gpiochip_irqchip_add() or
+gpiochip_irqchip_add_nested() is called.
To use the helpers please keep the following in mind:
@@ -323,6 +330,9 @@ When implementing an irqchip inside a GPIO driver, these two functions should
typically be called in the .startup() and .shutdown() callbacks from the
irqchip.
+When using the gpiolib irqchip helpers, these callback are automatically
+assigned.
+
Real-Time compliance for GPIO IRQ chips
---------------------------------------