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-rw-r--r--Documentation/gpio/driver.txt72
1 files changed, 12 insertions, 60 deletions
diff --git a/Documentation/gpio/driver.txt b/Documentation/gpio/driver.txt
index 9d7985171f07..90d0f6aba7a6 100644
--- a/Documentation/gpio/driver.txt
+++ b/Documentation/gpio/driver.txt
@@ -93,37 +93,22 @@ 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.
- NOTE: chained IRQ handlers are usually not good for real time. If you
- are submitting a new driver or refactoring a driver for real time compliance,
- consider using creating a nested/threaded irqchip instead, see below.
-
-* NESTED THREADED GPIO irqchips: these are traditionally 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, traffic which may in turn incur other IRQs to
- happen, cannot be handled in a quick IRQ handler with IRQs disabled.
-
- With the introduction of real time support in the Linux kernel, also other
- GPIO irqchips are encouraged to use a nested and threaded IRQ handler.
- Doing so makes the interrupts naturally preemptible on a real time
- setup, which means the system can easily be configured for real time with
- a (usually negligable) performance loss.
-
- These drivers spawn a thread and then mask the parent IRQ line until the
- interrupt is handled by the driver. The hallmark of this driver is to call
- something like this in its interrupt handler:
+* 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,
+ traffic which may in turn incur other IRQs to happen, cannot be handled
+ in a quick IRQ handler with IRQs disabled. Instead they need to spawn a
+ thread and then mask the parent IRQ line until the interrupt is handled
+ 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)
...
handle_nested_irq(irq);
- OR
- generic_handle_irq(irq);
- Threaded GPIO irqchips should set the .can_sleep flag on struct gpio_chip
- to true if they are e.g. accessing the chip over I2C or SPI, indicating that
- this chip may sleep when accessing the GPIOs. irqchips that are just made
- threaded to be preemptible and thus real time compliant need not do this:
- preemption is not sleeping.
+ The hallmark of threaded GPIO irqchips is that they set the .can_sleep
+ flag on struct gpio_chip to true, indicating that this chip may sleep
+ when accessing the GPIOs.
To help out in handling the set-up and management of GPIO irqchips and the
associated irqdomain and resource allocation callbacks, the gpiolib has
@@ -140,7 +125,7 @@ symbol:
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 threaded/nested irqchip if NULL is passed as handler.
+ to set up a nested irqchip if NULL is passed as handler.
To use the helpers please keep the following in mind:
@@ -185,39 +170,6 @@ 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. The
-following is a checklist to follow when preparing a driver for real
-time-compliance:
-
-- Nominally use raw_spinlock_t in the IRQ context path of the IRQ handler as
- we do not want these sections to be preempted.
-
-- Do NOT use chained_irq_enter() or chained_irq_exit() in the IRQ handler,
- as we want the hotpath to be preemptible.
-
-- Instead use nested IRQs and generic handlers such as handle_bad_irq(),
- handle_level_irq() and handle_edge_irq(). Consequentally the handler
- argument of gpiochip_set_chained_irqchip() should be NULL when using the
- gpiolib irqchip helpers.
-
-- Nominally set all handlers to handle_bad_irq() in the setup call, 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.
-
-- If you need to use the pm_runtime_get*()/pm_runtime_put*() callbacks in some
- of the irqchip callbacks, these should be moved to the .irq_bus_lock()
- and .irq_bus_unlock() callbacks respectively, as these are the only
- slowpath callbacks on an irqchip. Create the callbacks if need be.
-
-- Test your driver with the apropriate in-kernel real time test cases for both
- level and edge IRQs.
-
-
Requesting self-owned GPIO pins
-------------------------------