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    SubjectRe: [PATCH 5/8] RTC subsystem, dev interface
    Date
    On Sunday 08 January 2006 18:12, Alessandro Zummo wrote:
    > +
    > +static int rtc_dev_open(struct inode *inode, struct file *file)
    > +{
    > + int err;
    > + struct rtc_device *rtc = container_of(inode->i_cdev,
    > + struct rtc_device, char_dev);
    > + struct rtc_class_ops *ops = rtc->ops;
    > +
    > + /* We keep the lock as long as the device is in use
    > + * and return immediately if busy
    > + */
    > + if (down_trylock(&rtc->char_sem))
    > + return -EBUSY;
    > +

    Does the device have to be opened for exclusively? Can it support
    concurrent reads?


    > + file->private_data = &rtc->class_dev;
    > +
    > + err = ops->open ? ops->open(rtc->class_dev.dev) : 0;
    > + if (err == 0) {
    > +
    > + spin_lock_irq(&rtc->irq_lock);
    > + rtc->irq_data = 0;
    > + spin_unlock_irq(&rtc->irq_lock);
    > +
    > + return 0;
    > + }
    > +
    > + /* something has gone wrong, release the lock */
    > + up(&rtc->char_sem);
    > + return err;
    > +}
    > +
    > +
    > +static ssize_t
    > +rtc_dev_read(struct file *file, char __user *buf, size_t count, loff_t *ppos)
    > +{
    > + struct rtc_device *rtc = to_rtc_device(file->private_data);
    > +
    > + DECLARE_WAITQUEUE(wait, current);
    > + unsigned long data;
    > + ssize_t ret;
    > +
    > + if (count < sizeof(unsigned long))
    > + return -EINVAL;
    > +
    > + add_wait_queue(&rtc->irq_queue, &wait);
    > + do {
    > + __set_current_state(TASK_INTERRUPTIBLE);
    > +
    > + spin_lock_irq(&rtc->irq_lock);
    > + data = rtc->irq_data;
    > + rtc->irq_data = 0;
    > + spin_unlock_irq(&rtc->irq_lock);
    > +
    > + if (data != 0) {
    > + ret = 0;
    > + break;
    > + }
    > + if (file->f_flags & O_NONBLOCK) {
    > + ret = -EAGAIN;
    > + break;
    > + }
    > + if (signal_pending(current)) {
    > + ret = -ERESTARTSYS;
    > + break;
    > + }
    > + schedule();
    > + } while (1);
    > + set_current_state(TASK_RUNNING);
    > + remove_wait_queue(&rtc->irq_queue, &wait);
    > +


    The above looks very much like open-coded wait_event_interruptible();

    > + if (ret == 0) {
    > + ret = put_user(data, (unsigned long __user *)buf);
    > + if (ret == 0)
    > + ret = sizeof(unsigned long);
    > + }
    > + return ret;
    > +}
    > +
    > +static unsigned int rtc_dev_poll(struct file *file, poll_table *wait)
    > +{
    > + struct rtc_device *rtc = to_rtc_device(file->private_data);
    > + unsigned long data;
    > +
    > + poll_wait(file, &rtc->irq_queue, wait);
    > +
    > + spin_lock_irq(&rtc->irq_lock);
    > + data = rtc->irq_data;
    > + spin_unlock_irq(&rtc->irq_lock);
    > +
    > + return data != 0 ? POLLIN | POLLRDNORM : 0;
    > +}

    What does the lock above protect? Once it is released rtc->irq_data may
    change so reader that was woken up may not see any data anyway.

    > +static int rtc_dev_ioctl(struct inode *inode, struct file *file, unsigned int cmd,
    > + unsigned long arg)
    > +{
    > + int err = 0;
    > + struct class_device *class_dev = file->private_data;
    > + struct rtc_device *rtc = to_rtc_device(class_dev);
    > + struct rtc_class_ops *ops = rtc->ops;
    > + struct rtc_time tm;
    > + struct rtc_wkalrm alarm;
    > + void __user *uarg = (void __user *) arg;
    > +
    > + /* avoid conflicting IRQ users */
    > + if (cmd == RTC_PIE_ON || cmd == RTC_PIE_OFF || cmd == RTC_IRQP_SET) {
    > + spin_lock(&rtc->irq_task_lock);
    > + if (rtc->irq_task)
    > + err = -EBUSY;
    > + spin_unlock(&rtc->irq_task_lock);
    > +
    > + if (err < 0)
    > + return err;
    > + }
    > +
    > + /* try the driver's ioctl interface */
    > + if (ops->ioctl) {
    > + err = ops->ioctl(class_dev->dev, cmd, arg);
    > + if (err < 0 && err != -EINVAL)
    > + return err;
    > + }
    > +
    > + /* if the driver does not provide the ioctl interface
    > + * or if that particular ioctl was not implemented
    > + * (-EINVAL), we will try to emulate here.
    > + */
    > +
    > + switch (cmd) {
    > + case RTC_ALM_READ:
    > + if ((err = rtc_read_alarm(class_dev, &alarm)) < 0)
    > + return err;
    > +
    > + if ((err = copy_to_user(uarg, &alarm.time, sizeof(tm))))
    > + return -EFAULT;
    > + break;
    > +
    > + case RTC_ALM_SET:
    > + if ((err = copy_from_user(&alarm.time, uarg, sizeof(tm))))
    > + return -EFAULT;
    > +
    > + alarm.enabled = 0;
    > + alarm.pending = 0;
    > + alarm.time.tm_mday = -1;
    > + alarm.time.tm_mon = -1;
    > + alarm.time.tm_year = -1;
    > + alarm.time.tm_wday = -1;
    > + alarm.time.tm_yday = -1;
    > + alarm.time.tm_isdst = -1;
    > + err = rtc_set_alarm(class_dev, &alarm);
    > + break;
    > +
    > + case RTC_RD_TIME:
    > + if ((err = rtc_read_time(class_dev, &tm)) < 0)
    > + return err;
    > +
    > + if ((err = copy_to_user(uarg, &tm, sizeof(tm))))
    > + return -EFAULT;
    > + break;
    > +
    > + case RTC_SET_TIME:
    > + if (!capable(CAP_SYS_TIME))
    > + return -EACCES;
    > +
    > + if ((err = copy_from_user(&tm, uarg, sizeof(tm))))
    > + return -EFAULT;
    > +
    > + err = rtc_set_time(class_dev, &tm);
    > + break;
    > +#if 0
    > + case RTC_EPOCH_SET:
    > +#ifndef rtc_epoch
    > + /*
    > + * There were no RTC clocks before 1900.
    > + */
    > + if (arg < 1900) {
    > + err = -EINVAL;
    > + break;
    > + }
    > + if (!capable(CAP_SYS_TIME)) {
    > + err = -EACCES;
    > + break;
    > + }
    > + rtc_epoch = arg;
    > + err = 0;
    > +#endif
    > + break;
    > +
    > + case RTC_EPOCH_READ:
    > + err = put_user(rtc_epoch, (unsigned long __user *)uarg);
    > + break;
    > +#endif
    > + case RTC_WKALM_SET:
    > + if ((err = copy_from_user(&alarm, uarg, sizeof(alarm))))
    > + return -EFAULT;
    > +
    > + err = rtc_set_alarm(class_dev, &alarm);
    > + break;
    > +
    > + case RTC_WKALM_RD:
    > + if ((err = rtc_read_alarm(class_dev, &alarm)) < 0)
    > + return err;
    > +
    > + if ((err = copy_to_user(uarg, &alarm, sizeof(alarm))))
    > + return -EFAULT;
    > + break;
    > +
    > + default:
    > + err = -EINVAL;
    > + break;
    > + }
    > +
    > + return err;
    > +}
    > +
    > +static int rtc_dev_release(struct inode *inode, struct file *file)
    > +{
    > + struct rtc_device *rtc = to_rtc_device(file->private_data);
    > +
    > + if (rtc->ops->release)
    > + rtc->ops->release(rtc->class_dev.dev);
    > +
    > + spin_lock_irq(&rtc->irq_lock);
    > + rtc->irq_data = 0;
    > + spin_unlock_irq(&rtc->irq_lock);
    > +

    Why is the above needed?

    > + up(&rtc->char_sem);
    > + return 0;
    > +}
    > +
    > +static int rtc_dev_fasync(int fd, struct file *file, int on)
    > +{
    > + struct rtc_device *rtc = to_rtc_device(file->private_data);
    > + return fasync_helper(fd, file, on, &rtc->async_queue);
    > +}
    > +
    > +static struct file_operations rtc_dev_fops = {
    > + .owner = THIS_MODULE,
    > + .llseek = no_llseek,
    > + .read = rtc_dev_read,
    > + .poll = rtc_dev_poll,
    > + .ioctl = rtc_dev_ioctl,
    > + .open = rtc_dev_open,
    > + .release = rtc_dev_release,
    > + .fasync = rtc_dev_fasync,
    > +};
    > +
    > +static ssize_t rtc_dev_show_dev(struct class_device *class_dev, char *buf)
    > +{
    > + return print_dev_t(buf, class_dev->devt);
    > +}
    > +static CLASS_DEVICE_ATTR(dev, S_IRUGO, rtc_dev_show_dev, NULL);
    > +
    > +/* insertion/removal hooks */
    > +
    > +static int rtc_dev_add_device(struct class_device *class_dev,
    > + struct class_interface *class_intf)
    > +{
    > + struct rtc_device *rtc = to_rtc_device(class_dev);
    > +
    > + if (rtc->id >= RTC_DEV_MAX) {
    > + dev_err(class_dev->dev, "too many RTCs\n");
    > + return -EINVAL;
    > + }
    > +
    > + init_MUTEX(&rtc->char_sem);
    > + spin_lock_init(&rtc->irq_lock);
    > + init_waitqueue_head(&rtc->irq_queue);
    > +
    > + cdev_init(&rtc->char_dev, &rtc_dev_fops);
    > + rtc->char_dev.owner = rtc->owner;
    > + class_dev->devt = MKDEV(MAJOR(rtc_devt), rtc->id);
    > +
    > + if (cdev_add(&rtc->char_dev, class_dev->devt, 1)) {
    > + cdev_del(&rtc->char_dev);
    > +
    > + dev_err(class_dev->dev,
    > + "failed to add char device %d:%d\n",
    > + MAJOR(class_dev->devt),
    > + MINOR(class_dev->devt));
    > +
    > + class_dev->devt = MKDEV(0, 0);
    > + return -ENODEV;
    > + }
    > +
    > + class_device_create_file(class_dev, &class_device_attr_dev);
    > +
    > + dev_info(class_dev->dev, "rtc intf: dev (%d:%d)\n",
    > + MAJOR(class_dev->devt),
    > + MINOR(class_dev->devt));
    > +
    > + kobject_hotplug(&class_dev->kobj, KOBJ_ADD);
    > +

    This is kobject_hotplug abuse; you are not adding a new object here.

    > + return 0;
    > +}
    > +
    > +static void rtc_dev_remove_device(struct class_device *class_dev,
    > + struct class_interface *class_intf)
    > +{
    > + struct rtc_device *rtc = to_rtc_device(class_dev);
    > +
    > + class_device_remove_file(class_dev, &class_device_attr_dev);
    > +
    > + if (MAJOR(class_dev->devt)) {
    > + dev_dbg(class_dev->dev, "removing char %d:%d\n",
    > + MAJOR(class_dev->devt),
    > + MINOR(class_dev->devt));
    > + cdev_del(&rtc->char_dev);
    > +
    > + kobject_hotplug(&class_dev->kobj, KOBJ_REMOVE);
    > +

    Same here...

    > + class_dev->devt = MKDEV(0, 0);
    > + }
    > +}
    > +
    > +/* interface registration */
    > +
    > +struct class_interface rtc_dev_interface = {
    > + .add = &rtc_dev_add_device,
    > + .remove = &rtc_dev_remove_device,
    > +};
    > +

    I wonder if doing rtc dev as a class device interface is a good idea.
    It may be cleaner to fold it into the core.

    > +static int __init rtc_dev_init(void)
    > +{
    > + int err;
    > +
    > + if ((err = alloc_chrdev_region(&rtc_devt, 0, RTC_DEV_MAX, "rtc")) < 0) {
    > + printk(KERN_ERR "%s: failed to allocate char dev region\n",
    > + __FILE__);
    > + return err;
    > + }
    > +
    > + if ((err = rtc_interface_register(&rtc_dev_interface)) < 0) {
    > + printk(KERN_ERR "%s: failed to register the interface\n",
    > + __FILE__);
    > + unregister_chrdev_region(rtc_devt, RTC_DEV_MAX);
    > + return err;
    > + }
    > +
    > + return 0;
    > +}
    > +
    > +static void __exit rtc_dev_exit(void)
    > +{
    > + class_interface_unregister(&rtc_dev_interface);
    > +
    > + unregister_chrdev_region(rtc_devt, RTC_DEV_MAX);
    > +}
    > +
    > +module_init(rtc_dev_init);
    > +module_exit(rtc_dev_exit);
    > +
    > +MODULE_AUTHOR("Alessandro Zummo <a.zummo@towertech.it>");
    > +MODULE_DESCRIPTION("RTC class dev interface");
    > +MODULE_LICENSE("GPL");
    > --- linux-nslu2.orig/drivers/rtc/Kconfig 2006-01-04 01:27:14.000000000 +0100
    > +++ linux-nslu2/drivers/rtc/Kconfig 2006-01-04 01:27:15.000000000 +0100
    > @@ -41,6 +41,17 @@ config RTC_INTF_PROC
    > This driver can also be built as a module. If so, the module
    > will be called rtc-proc.
    >
    > +config RTC_INTF_DEV
    > + tristate "dev"
    > + depends on RTC_CLASS
    > + default RTC_CLASS
    > + help
    > + Say yes here if you want to use your RTC using the dev
    > + interface, /dev/rtc .
    > +
    > + This driver can also be built as a module. If so, the module
    > + will be called rtc-dev.
    > +
    > comment "RTC drivers"
    > depends on RTC_CLASS
    >
    > --- linux-nslu2.orig/drivers/rtc/Makefile 2006-01-04 01:27:14.000000000 +0100
    > +++ linux-nslu2/drivers/rtc/Makefile 2006-01-04 01:27:15.000000000 +0100
    > @@ -7,3 +7,4 @@ obj-$(CONFIG_RTC_CLASS) += rtc-core.o
    > rtc-core-y := class.o interface.o
    > obj-$(CONFIG_RTC_INTF_SYSFS) += rtc-sysfs.o
    > obj-$(CONFIG_RTC_INTF_PROC) += rtc-proc.o
    > +obj-$(CONFIG_RTC_INTF_DEV) += rtc-dev.o
    >
    > --
    > -
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    >

    --
    Dmitry
    -
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