Interrupt handling. Interrupt handling. Deferred work. Interrupt handling. Remove an interrupt handler. 1. Link a struct work to a function

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1 Interrupt handling Interrupt handling error = request_irq(irq_number, interrupt_service_routine, flags, module_name, (void*)dataptr); error: == 0 OK!= 0 FAILED interrupt_service_routine: irqreturn_t interrupt_service_routine(int irq_number, void *dataptr); flags one or more: IRQF_SHARED IRQF_TRIGGER_RISING IRQF_TRIGGER_FALLING interrupt_service_routine: irqreturn_t interrupt_service_routine(int irq_number, void *dataptr); No process context No current No copy_from_user or copy_to_user No sleeping No semaphores or mutexes No kmalloc(, GFP_KERNEL) No msleep or ssleep Shared interrupt: check if it is your interrupt (use dataptr) Be fast (defer work if needed) Return IRQ_NONE or IRQ_HANDLED Interrupt handling Deferred work Remove an interrupt handler free_irq(irq_number, dataptr); 1. Link a struct work to a function INIT_WORK(&userdata->work, workfunction); 2a. Create a queue of works (struct workqueue_struct) qptr = create_workqueue("workqueue name"); qptr = create_singlethread_workqueue("workqueue name"); 3a. Add the work to the queue queue_work(qptr, &userdata->work); queue_delayed_work(qptr, &userdata->work, delay); 2b. Add the work to a shared queue schedule_work(&userdata->work);

2 Deferred work Deferred work Safely remove a private workqueue destroy_workqueue(device.wq); Safely remove a work from shared queue cancel_work_sync(&device.work); #include <linux/workqueue.h> /* struct to keep user data and work info */ struct mystruct struct work_struct work; userdata; void workfunction(struct work_struct *work) /* deferred work function */ INIT_WORK(&userdata->work, workfunction); wq = create_singlethread_workqueue("workqueue_name");. queue_work(wq, &userdata.work); /* use a private workqueue */ Deferred work Delay (long) #include <linux/workqueue.h> /* struct to keep user data and work info */ struct mystruct struct work_struct work; userdata; delay = delay_seconds*hz; wait_queue_head_t waitq; init_waitqueue_head(&waitq); wait_event_interruptible_timeout(waitq, 0, delay); /* wait until timeout or somebody calls wake_up on waitq return value: 0 => timeout expired > 0 => remaining delay */ void workfunction(struct work_struct *work) /* deferred work function */ INIT_WORK(&userdata->work, workfunction); schedule_work(&userdata->work); /* use a default (shared) workqueue */ delay = delay_seconds*hz; set_current_state(task_interruptible); schedule_timeout(delay); /* return value: 0 => timeout expired > 0 => remaining delay */

3 Delay (short) Timers /* scheduled wait */ msleep(delay_in_ms); msleep_interruptible(delay_in_ms); ssleep(delay_in_s); /* busy wait */ ndelay(delay_in_ns); udelay(delay_in_us); mdelay(delay_in_ms); void timer_function(unsigned long timerdata) /* will run at interrupt time (on the same CPU which registered it) no access at user space current is meaningless no sleeping no kmalloc(, GFP_KERNEL) no semaphores no schedule() no wait_event */ add_timer(); // if needed struct timer_list T = TIMER_INITIALIZER(timer_function, jiffies+delay, timerdata); add_timer(&t); /* others; int timer_pending(const struct timer_list * timer); int mod_timer(struct timer_list *timer, unsigned long new_expires); int del_timer(struct timer_list * timer); int del_timer_sync(struct timer_list * timer); (may sleep) */ GPIO functions int gpio_is_valid(int pin_idx);!= 0 : pin is valid == 0 : pin is not valid int gpio_request(int pin_idx, char *pin_label /* optional */); < 0 : error void gpio_free(int pin_idx); int gpio_cansleep(int pin_idx);!= 0 : access to pin can sleep int gpio_direction_input(int pin_idx); < 0 : error Use a pushbutton to pulse a led (if not already pulsing) Button press irq deferred scheduling of a pulsing function Write: change the number of pulses and activate pulsing (if not already active) Read: get the number of pulses (default or last written) int gpio_direction_output(int pin_idx, int pin_value); < 0 : error void gpio_set_value(int pin_idx, int pin_value); int gpio_get_value(int pin_idx); int gpio_to_irq(int pin_idx); < 0 : error >= 0 irq related to pin Keep track of: Total number of pulses performed Total number of IRQs received Total number of IRQs actually handled

4 Module initialization Register a major number Reserve needed GPIOs Request an IRQ Connect to interrupt service routine Prepare deferred work Create an entry in /proc/driver Module cleanup Free the /proc/driver entry Free the IRQ Free GPIOs Remove deferred work #ifndef _IRQCE2_H_INCLUDED #define _IRQCE2_H_INCLUDED #define LINE_IN 7 #define LINE_OUT 139 #ifdef CONFIG_MACH_OMAP3_BEAGLE #define LED_OUT 149 #else #define LED_OUT 0 #endif #define PULSE_DELAY_MS 300 #define DEFAULT_NPULSES 3 #define MAX_NPULSES 10 #define MODNAME "irqce2" On beagleboard: 7: GPIO connected to a pushbutton 139: GPIO connected to expansion header 149: GPIO connected to a board led We pulse on line_out and on led_out There is no warranty we are really writing on a led. To be safe: - use a fixed value for LED_OUT (no module parameter); - ensure we are running on a beagleboard by checking the macro CONFIG_MACH_OMAP3_BEAGLE) irq_ce2.h typedef struct struct cdev cdev; /* char device structure */ struct semaphore sem; /* synchronization */ unsigned npulses; /* pulses to do each time */ unsigned long pulses_done; /* overall pulses performed */ int irq; /* irq reserved for device */ unsigned long irq_received; unsigned long irq_handled; int pulsing; /* currently pulsing */ spinlock_t pulsing_lock; /* setting pulsing must be atomic */ int last_input; /* last value read on input pin */ int last_output; /* last value written on input pin */ int can_read; /* only one read */ int can_write; /* only one write */ extern struct file_operations irqce2_funcs; int irqce2_init_module(void); void irqce2_cleanup_module(void); irqreturn_t irqce2_isr(int irq, void *dev_id); void pulsefunction(struct work_struct *work); int read_procmem(char *buf, char **start, off_t offset, int count, int *eof, void *data); #endif /* _IRQCE2_H_INCLUDED */ struct work_struct work; /* for deferred work */ struct workqueue_struct *wq; irqce2_device_descr; irq_ce2.h irq_ce2.h

5 #include <linux/module.h> #include <linux/moduleparam.h> #include <linux/init.h> #include <linux/kernel.h> #include <linux/fs.h> #include <linux/errno.h> #include <linux/slab.h> #include <linux/types.h> #include <asm/system.h> #include <asm/uaccess.h> #include <linux/fcntl.h> #include <linux/proc_fs.h> #include <linux/seq_file.h> #include <linux/cdev.h> #include <linux/interrupt.h> #include <linux/sched.h> #include <linux/delay.h> #include <linux/gpio.h> #include "irq_ce2.h" MODULE_AUTHOR("Calcolatori Elettronici 2 (uniud)"); MODULE_DESCRIPTION("Example for irq and deferred work"); MODULE_VERSION("0:1.0"); MODULE_LICENSE("Dual BSD/GPL"); /* parameters */ int line_in = LINE_IN; int line_out = LINE_OUT; Default values int pulsems = PULSE_DELAY_MS; /* permission flag: S_IRUSR / S_IWUSR / S_IXUSR : read / write / exec for user (owner) S_IRWXU: read-write-exec for user S_IRGRP, S_IWGRP, S_IXGRP, S_IRWXG: permissions for group S_IROTH, S_IWOTH, S_IXOTH, S_IRWXO: permissions for others S_IRUGO / S_IWUGO / S_IXUGO: read / write / exec for all S_IRWXUGO: read-write-exec for all */ module_param(line_in, int, S_IRUGO); module_param(line_out, int, S_IRUGO); Default values can be overridden at load time module_param(pulsems, int, S_IRUGO); (we use 0 for line_in or line_out to not use such pins) /* globals */ irqce2_device_descr device; int major = 0; int minor = 0; /* allocate gpio pins line_in and line_out */ int allocate_pins(void) int ret; if ( (line_in &&!gpio_is_valid(line_in)) (line_out &&!gpio_is_valid(line_out)) ) if (line_in) ret = gpio_request(line_in, "v"); if (ret < 0) ret = gpio_direction_input(line_in); if (ret < 0) goto fail1; Ensure we are using valid GPIOs Require the input pin if (line_out) ret = gpio_request(line_out, "^"); if (ret < 0) goto fail1; ret = gpio_direction_output(line_out, 0); if (ret < 0) goto fail2; if ( (line_in && gpio_cansleep(line_in)) (line_out && gpio_cansleep(line_out)) ) goto fail2; if ( LED_OUT && gpio_cansleep(led_out) ) goto fail2; return 1; /* OK */ Require the output pin (led is already allocated) We need non-sleeping GPIOs

6 fail2: if (line_out) gpio_free(line_out); fail1: if (line_in) gpio_free(line_in); /* FAIL */ /* release gpio pins line_in and line_out */ void free_pins(void) if (line_out) gpio_free(line_out); if (line_in) gpio_free(line_in); /* allocate irq for line_in */ int allocate_irq(void) int irq; int error; if (!line_in) return 1; irq = gpio_to_irq(line_in); if (irq < 0) error = irq; printk(kern_info MODNAME ": Unable to get irq: error %d\n", error); error = request_irq(irq, irqce2_isr, IRQF_SHARED IRQF_TRIGGER_RISING IRQF_TRIGGER_FALLING, MODNAME, (void*)&device); Shared IRQ, triggered by both rising and falling signal edge (actually falling edge is not used in isr) if (error) printk(kern_info MODNAME ": Unable to claim irq %d; error %d\n", irq, error); device.irq = irq; return 1;

7 /* release irq for line_in */ void release_irq(void) if (!line_in) return; free_irq(device.irq, &device); or: free_irq(gpio_to_irq(line_in), &device); /* write on pin line_out and on led LED_OUT */ void writeoutpin(int v) if (line_out) gpio_set_value(line_out, v); if (LED_OUT) gpio_set_value(led_out, v); device.last_output = v; /* read from pin line_in */ int readinpin(void) if (line_in) return gpio_get_value(line_in); else /* driver interrupt handler */ irqreturn_t irqce2_isr(int irq, void *dev_id) irqce2_device_descr *d = dev_id; int lineval; unsigned long irqflags; d->irq_received++; lineval = readinpin(); if ( lineval == d->last_input ) return IRQ_NONE; /* not on my line */ else d->last_input = lineval; d->irq_handled++; Shared IRQ: test if this is for me if ( d->last_input == 1 ) /* critical section: Rising edge: button is pressed 1. no semaphores in interrupt handlers 2. for lock used within interrupt handlers the safe version (spin_lock_irqsave and spin_unlock_irqrestore) must be used */ spin_lock_irqsave(&device.pulsing_lock, irqflags); if (! d->pulsing ) /* activate pulses on output */ d->pulsing = 1; #ifdef USE_SHARED_QUEUE schedule_work(&device.work); #else queue_work(device.wq, &device.work); #endif spin_unlock_irqrestore(&device.pulsing_lock, irqflags); Access to pulsing and deferred work scheduling must be exclusive return IRQ_HANDLED;

8 /* driver interface functions */ /* Module init */ int init irqce2_init_module(void) dev_t dev = 0; int err, devno; err = alloc_chrdev_region(&dev, minor, 1, MODNAME); major = MAJOR(dev); if (err < 0) printk(kern_warning MODNAME ": can't get major %d\n", major); return err; devno = MKDEV(major, 0); memset(&device, 0, sizeof(irqce2_device_descr)); if (!allocate_pins() ) printk(kern_info MODNAME ": Failed to allocate pins\n"); err = -ENOSR; goto fail1; if ( line_in &&!allocate_irq() ) printk(kern_info MODNAME ": Failed to allocate irq\n"); err = -ENOSR; goto fail2; sema_init(&device.sem, 1); cdev_init(&device.cdev, &irqce2_funcs); device.cdev.owner = THIS_MODULE; device.cdev.ops = &irqce2_funcs; device.npulses = DEFAULT_NPULSES; device.can_read = 1; device.can_write = 1; device.pulsing_lock = SPIN_LOCK_UNLOCKED; INIT_WORK(&device.work, pulsefunction); #ifndef USE_SHARED_QUEUE /* pulsefunction will sleep hence use a private workqueue */ device.wq = create_singlethread_workqueue(modname "WQ"); #endif err = cdev_add (&device.cdev, devno, 1); /* device is live now */ if (err) /* registration failed */ printk(kern_notice MODNAME ": Error %d adding device\n", err); goto fail3; create_proc_read_entry("driver/" MODNAME, /* name */ 0, /* mode (0:default) */ NULL, /* parent dir */ read_procmem, NULL /* client data */); /* OK */ fail3: if (line_in) release_irq(); fail2: free_pins(); fail1: unregister_chrdev_region(devno, 1); return err; /* FAIL */ /* Module cleanup */ void exit irqce2_cleanup_module(void) int devno; remove_proc_entry("driver/" MODNAME, NULL); if (line_in) release_irq(); free_pins(); cdev_del(&device.cdev); devno = MKDEV(major, minor); unregister_chrdev_region(devno, 1); #ifdef USE_SHARED_QUEUE cancel_work_sync(&device.work); #else destroy_workqueue(device.wq); #endif

9 /* Device open */ int irqce2_open(struct inode *inode, struct file *file) irqce2_device_descr *dev; dev = container_of(inode->i_cdev, irqce2_device_descr, cdev); file->private_data = dev; dev->can_read = 1; dev->can_write = 1; /* Device close */ int irqce2_release(struct inode *inode, struct file *file) /* Read */ ssize_t irqce2_read(struct file *file, char *buffer, size_t count, loff_t *offset) irqce2_device_descr *d = file->private_data; char buff[80]; ssize_t ret = 0; int datalen; if (down_interruptible(&d->sem)) return -ERESTARTSYS; if ( d->can_read ) sprintf(buff, "npulses: %d\n", d->npulses); datalen = strlen(buff); if ( copy_to_user(buffer, buff, datalen) ) ret = -EFAULT; else *offset += datalen; ret = datalen; d->can_read = 0; else ret = 0; up(&d->sem); return ret; /* Write */ ssize_t irqce2_write(struct file *file, const char *buffer, size_t count, loff_t *offset) irqce2_device_descr *d = file->private_data; unsigned long irqflags; char buff[80]; ssize_t ret = 0; int npulses; if (down_interruptible(&d->sem)) return -ERESTARTSYS; if ( d->can_write &! d->pulsing ) if (count >= sizeof(buff)) count = sizeof(buff)-1; if (copy_from_user(buff, buffer, count)) ret = -EFAULT; else buff[sizeof(buff)-1] = 0; if (! sscanf(buff, "%d", &npulses) ) /* invalid input */ ret = 0; else if (npulses > MAX_NPULSES) npulses = MAX_NPULSES; ret = count;

10 spin_lock_irqsave(&device.pulsing_lock, irqflags); if (! d->pulsing ) d->npulses = npulses; *offset += count; ret = count; d->can_write = 0; d->pulsing = 1; #ifdef USE_SHARED_QUEUE schedule_work(&d->work); #else queue_work(d->wq, &d->work); #endif else ret = 0; spin_unlock_irqrestore(&device.pulsing_lock, irqflags); else ret = 0; up(&d->sem); return count; Access to pulsing and deferred work scheduling must be exclusive /* Deferred work */ void pulsefunction(struct work_struct *work) irqce2_device_descr *d = container_of(work, irqce2_device_descr, work); unsigned long irqflags; int i; for (i=0 ; i<d->npulses ; i++) writeoutpin(1); msleep(pulsems); writeoutpin(0); d->pulses_done++; if (i<d->npulses) msleep(pulsems); spin_lock_irqsave(&device.pulsing_lock, irqflags); d->pulsing = 0; spin_unlock_irqrestore(&device.pulsing_lock, irqflags); /* Proc file function */ int read_procmem(char *buf, char **start, off_t offset, int count, int *eof, void *data) const char formatstr[] = "IRQ is %d, npulses is %d\n" "Received %ld irqs, %ld handled\n" "Generated %ld pulses\n"; char str[sizeof(formatstr)+5*9*2]; struct file_operations irqce2_funcs = owner: THIS_MODULE, open: irqce2_open, release: irqce2_release, read: irqce2_read, write: irqce2_write, ; sprintf(str, formatstr, device.irq, device.npulses, device.irq_received, device.irq_handled, device.pulses_done); strncpy(buf, str, count-1); buf[count-1] = 0; *eof = 1; return strlen(buf); module_init(irqce2_init_module); module_exit(irqce2_cleanup_module);

11 # If KERNELRELEASE is defined, we've been invoked from the # kernel build system and can use its language. ifneq ($(KERNELRELEASE),) obj-m := irq_ce2.o # Otherwise we were called directly from the command # line; invoke the kernel build system. else KERNELDIR?= /lib/modules/$(shell uname -r)/build PWD := $(shell pwd) default: $(MAKE) -C $(KERNELDIR) M=$(PWD) modules endif $ insmod./irq_ce2.ko $ lsmod $ ls /sys/module/irq_ce2/parameters/ $ cat /sys/module/irq_ce2/parameters/pulsems $ cat /proc/kallsyms grep irqce2 $ cat /proc/interrupts $ cat /proc/devices grep irqce2 $ mknod e c press the pushbutton (and see the led pulsing) $ echo 5 > e Test 1 (shared workqueue) Build with: make \ KERNELDIR=<binary_kernel_dir> \ ARCH=arm \ CROSS_COMPILE=arm-none-linux-gnueabi- \ EXTRA_CFLAGS=-DUSE_SHARED_QUEUE $ echo 5 > e ; while true ; do echo -n "a " ; sleep 1 ; done $ cat /proc/driver/irqce2 Makefile $ cat e $ rmmod irq_ce2 Test 2 (private workqueue) Build with: make \ KERNELDIR=<binary_kernel_dir> \ ARCH=arm \ CROSS_COMPILE=arm-none-linux-gnueabi- After module rebuilding, perform previous test again

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