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jservBob Mottram
jserv
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Bob Mottram
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Provide a tasklet-free example
Co-authored-by: Bob Mottram <[email protected]>
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‎.ci/non-working

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@@ -1,3 +1,4 @@
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bottomhalf
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bh_threaded
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intrpt
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vkbd

‎examples/Makefile

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@@ -26,6 +26,7 @@ obj-m += example_rwlock.o
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obj-m += example_atomic.o
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obj-m += example_mutex.o
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obj-m += bottomhalf.o
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obj-m += bh_threaded.o
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obj-m += ioctl.o
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obj-m += vinput.o
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obj-m += vkbd.o

‎examples/bh_threaded.c

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/*
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* bh_thread.c - Top and bottom half interrupt handling
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*
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* Based upon the RPi example by Stefan Wendler ([email protected])
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* from:
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* https://github.com/wendlers/rpi-kmod-samples
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*
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* Press one button to turn on a LED and another to turn it off
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*/
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#include <linux/module.h>
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#include <linux/kernel.h>
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#include <linux/gpio.h>
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#include <linux/delay.h>
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#include <linux/interrupt.h>
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static int button_irqs[] = { -1, -1 };
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/* Define GPIOs for LEDs.
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* FIXME: Change the numbers for the GPIO on your board.
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*/
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static struct gpio leds[] = { { 4, GPIOF_OUT_INIT_LOW, "LED 1" } };
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/* Define GPIOs for BUTTONS
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* FIXME: Change the numbers for the GPIO on your board.
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*/
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static struct gpio buttons[] = {
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{ 17, GPIOF_IN, "LED 1 ON BUTTON" },
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{ 18, GPIOF_IN, "LED 1 OFF BUTTON" },
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};
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/* This happens immediately, when the IRQ is triggered */
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static irqreturn_t button_top_half(int irq, void *ident)
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{
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return IRQ_WAKE_THREAD;
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}
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/* This can happen at leisure, freeing up IRQs for other high priority task */
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static irqreturn_t button_bottom_half(int irq, void *ident)
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{
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pr_info("Bottom half task starts\n");
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mdelay(500); /* do something which takes a while */
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pr_info("Bottom half task ends\n");
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return IRQ_HANDLED;
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}
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static int __init bottomhalf_init(void)
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{
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int ret = 0;
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pr_info("%s\n", __func__);
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/* register LED gpios */
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ret = gpio_request_array(leds, ARRAY_SIZE(leds));
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if (ret) {
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pr_err("Unable to request GPIOs for LEDs: %d\n", ret);
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return ret;
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}
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/* register BUTTON gpios */
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ret = gpio_request_array(buttons, ARRAY_SIZE(buttons));
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if (ret) {
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pr_err("Unable to request GPIOs for BUTTONs: %d\n", ret);
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goto fail1;
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}
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pr_info("Current button1 value: %d\n", gpio_get_value(buttons[0].gpio));
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ret = gpio_to_irq(buttons[0].gpio);
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if (ret < 0) {
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pr_err("Unable to request IRQ: %d\n", ret);
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goto fail2;
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}
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button_irqs[0] = ret;
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pr_info("Successfully requested BUTTON1 IRQ # %d\n", button_irqs[0]);
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ret = request_threaded_irq(
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gpio_to_irq(button_irqs[0]), button_top_half, button_bottom_half,
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IRQF_TRIGGER_RISING | IRQF_TRIGGER_FALLING, "gpiomod#button1", NULL);
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if (ret) {
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pr_err("Unable to request IRQ: %d\n", ret);
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goto fail2;
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}
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ret = gpio_to_irq(buttons[1].gpio);
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if (ret < 0) {
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pr_err("Unable to request IRQ: %d\n", ret);
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goto fail2;
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}
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button_irqs[1] = ret;
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pr_info("Successfully requested BUTTON2 IRQ # %d\n", button_irqs[1]);
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ret = request_threaded_irq(
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gpio_to_irq(button_irqs[1]), button_top_half, button_bottom_half,
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IRQF_TRIGGER_RISING | IRQF_TRIGGER_FALLING, "gpiomod#button2", NULL);
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if (ret) {
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pr_err("Unable to request IRQ: %d\n", ret);
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goto fail3;
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}
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return 0;
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/* cleanup what has been setup so far */
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fail3:
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free_irq(button_irqs[0], NULL);
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fail2:
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gpio_free_array(buttons, ARRAY_SIZE(leds));
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fail1:
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gpio_free_array(leds, ARRAY_SIZE(leds));
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return ret;
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}
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static void __exit bottomhalf_exit(void)
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{
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int i;
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pr_info("%s\n", __func__);
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/* free irqs */
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free_irq(button_irqs[0], NULL);
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free_irq(button_irqs[1], NULL);
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/* turn all LEDs off */
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for (i = 0; i < ARRAY_SIZE(leds); i++)
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gpio_set_value(leds[i].gpio, 0);
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/* unregister */
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gpio_free_array(leds, ARRAY_SIZE(leds));
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gpio_free_array(buttons, ARRAY_SIZE(buttons));
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}
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module_init(bottomhalf_init);
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module_exit(bottomhalf_exit);
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MODULE_LICENSE("GPL");
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MODULE_DESCRIPTION("Interrupt with top and bottom half");

‎lkmpg.tex

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@@ -1818,6 +1818,10 @@ \section{Scheduling Tasks}
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Tasklets are a quick and easy way of scheduling a single function to be run.
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For example, when triggered from an interrupt, whereas work queues are more complicated but also better suited to running multiple things in a sequence.
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It is possible that in future tasklets may be replaced by \textit{threaded irqs}.
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However, discussion about that has been ongoing since 2007 (\href{https://lwn.net/Articles/239633}{Eliminating tasklets}), so do not hold your breath.
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See the section \ref{sec:irq} if you wish to avoid the tasklet debate.
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\subsection{Tasklets}
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\label{sec:tasklet}
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Here is an example tasklet module.
@@ -1925,6 +1929,37 @@ \subsection{Bottom Half}
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\samplec{examples/bottomhalf.c}
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\subsection{Threaded IRQ}
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Threaded IRQ is a mechanism to handle both top-half and bottom-half of an IRQ at once.
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A threaded IRQ splits one handler into two: one for the top-half, the other for the bottom-half.
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Those two handlers are registered at once by \cpp|request_threaded_irq()|.
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The top-half handler runs in interrupt context.
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It's the equivalence of the handler passed to the \cpp|request_irq()|.
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The bottom-half handler on the other hand runs in its own thread.
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This thread is created on registration of a threaded IRQ. Its sole purpose is to run this bottom-half handler.
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This is where a threaded IRQ is ``threaded''.
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Whether the bottom-half handler will be invoked is determined by the return value of the top-half handler.
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If \cpp|IRQ_WAKE_THREAD| is returned, that bottom-half serving thread will wake up.
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The thread then runs the bottom-half handler.
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Here is an example of how to do the same thing as before, with top and bottom halves, but using threads.
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\samplec{examples/bh_threaded.c}
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\cpp|request_threaded_irq()| only takes one additional parameter than the \cpp|request_irq()| -- the bottom-half handling function that runs in its own thread.
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In this example it is the \cpp|button_bottom_half()|.
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Usage of other parameters are the same as \cpp|request_irq()|.
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Presence of both handlers is not mandatory.
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If either of them is not needed, pass the \cpp|NULL| instead.
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A \cpp|NULL| top-half handler implicitly means doing nothing but waking up the bottom-half serving thread; A \cpp|NULL| bottom-half handler will have the same effect as \cpp|request_irq()|.
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In fact, this is how \cpp|request_irq()| is implemented.
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Note that passing \cpp|NULL| as both handlers is considered an error and will make registration fail.
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\section{Virtual Input Device Driver}
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\label{sec:vinput}
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The input device driver is a module that provides a way to communicate with the interaction device via the event.

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