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    SubjectRe: [RFC][PATCH 4/7] Input / PM: Add ioctl to block suspend while event queue is not empty
    Date
    On Friday, February 24, 2012, Matt Helsley wrote:
    > On Wed, Feb 22, 2012 at 12:34:58AM +0100, Rafael J. Wysocki wrote:
    > > From: Arve Hjønnevåg <arve@android.com>
    > >
    > > Add a new ioctl, EVIOCSWAKEUPSRC, to attach a wakeup source object to
    > > an evdev client event queue, such that it will be active whenever the
    > > queue is not empty. Then, all events in the queue will be regarded
    > > as wakeup events in progress and pm_get_wakeup_count() will block (or
    > > return false if woken up by a signal) until they are removed from the
    > > queue. In consequence, if the checking of wakeup events is enabled
    > > (e.g. throught the /sys/power/wakeup_count interface), the system
    > > won't be able to go into a sleep state until the queue is empty.
    > >
    > > This allows user space processes to handle situations in which they
    > > want to do a select() on an evdev descriptor, so they go to sleep
    > > until there are some events to read from the device's queue, and then
    > > they don't want the system to go into a sleep state until all the
    > > events are read (presumably for further processing). Of course, if
    > > they don't want the system to go into a sleep state _after_ all the
    > > events have been read from the queue, they have to use a separate
    > > mechanism that will prevent the system from doing that and it has
    > > to be activated before reading the first event (that also may be the
    > > last one).
    >
    > I haven't seen this idea mentioned before but I must admit I haven't
    > been following this thread too closely so apologies (and don't bother
    > rehashing) if it has:
    >
    > Could you just add this to epoll so that any fd userspace chooses would be
    > capable of doing this without introducing potentially ecclectic ioctl
    > interfaces?
    >
    > struct epoll_event ev;
    >
    > epfd = epoll_create1(EPOLL_STAY_AWAKE_SET);
    > ev.data.ptr = foo;
    > epoll_ctl(epfd, EPOLL_CTL_ADD, fd, &ev);
    >
    > Which could be useful because you can put one epollfd in another's epoll
    > set. Or maybe as an EPOLLKEEPAWAKE flag in the event struct sort of like
    > EPOLLET:
    >
    > epfd = epoll_create1(0);
    > ev.events = EPOLLIN|EPOLLKEEPAWAKE;
    > epoll_ctl(epfd, EPOLL_CTL_ADD, fd, &ev);

    Do you mean something like the patch below, or something different?

    Rafael

    ---
    drivers/input/evdev.c | 55 ++++++++++++++++++++++++++++++++++++++++++++++
    fs/eventpoll.c | 15 +++++++++++-
    include/linux/eventpoll.h | 6 +++++
    include/linux/fs.h | 1
    4 files changed, 76 insertions(+), 1 deletion(-)

    Index: linux/include/linux/fs.h
    ===================================================================
    --- linux.orig/include/linux/fs.h
    +++ linux/include/linux/fs.h
    @@ -1604,6 +1604,7 @@ struct file_operations {
    ssize_t (*aio_write) (struct kiocb *, const struct iovec *, unsigned long, loff_t);
    int (*readdir) (struct file *, void *, filldir_t);
    unsigned int (*poll) (struct file *, struct poll_table_struct *);
    + void (*epoll_ctl) (struct file *, int, unsigned int);
    long (*unlocked_ioctl) (struct file *, unsigned int, unsigned long);
    long (*compat_ioctl) (struct file *, unsigned int, unsigned long);
    int (*mmap) (struct file *, struct vm_area_struct *);
    Index: linux/fs/eventpoll.c
    ===================================================================
    --- linux.orig/fs/eventpoll.c
    +++ linux/fs/eventpoll.c
    @@ -609,6 +609,10 @@ static int ep_remove(struct eventpoll *e
    unsigned long flags;
    struct file *file = epi->ffd.file;

    + /* Notify the underlying driver that the polling has completed */
    + if (file->f_op->epoll_ctl)
    + file->f_op->epoll_ctl(file, EPOLL_CTL_DEL, epi->event.events);
    +
    /*
    * Removes poll wait queue hooks. We _have_ to do this without holding
    * the "ep->lock" otherwise a deadlock might occur. This because of the
    @@ -1094,6 +1098,10 @@ static int ep_insert(struct eventpoll *e
    epq.epi = epi;
    init_poll_funcptr(&epq.pt, ep_ptable_queue_proc);

    + /* Notify the underlying driver that we want to poll it */
    + if (tfile->f_op->epoll_ctl)
    + tfile->f_op->epoll_ctl(tfile, EPOLL_CTL_ADD, event->events);
    +
    /*
    * Attach the item to the poll hooks and get current event bits.
    * We can safely use the file* here because its usage count has
    @@ -1185,6 +1193,7 @@ error_unregister:
    */
    static int ep_modify(struct eventpoll *ep, struct epitem *epi, struct epoll_event *event)
    {
    + struct file *file = epi->ffd.file;
    int pwake = 0;
    unsigned int revents;

    @@ -1196,11 +1205,15 @@ static int ep_modify(struct eventpoll *e
    epi->event.events = event->events;
    epi->event.data = event->data; /* protected by mtx */

    + /* Notify the underlying driver of the change */
    + if (file->f_op->epoll_ctl)
    + file->f_op->epoll_ctl(file, EPOLL_CTL_MOD, event->events);
    +
    /*
    * Get current event bits. We can safely use the file* here because
    * its usage count has been increased by the caller of this function.
    */
    - revents = epi->ffd.file->f_op->poll(epi->ffd.file, NULL);
    + revents = file->f_op->poll(file, NULL);

    /*
    * If the item is "hot" and it is not registered inside the ready
    Index: linux/drivers/input/evdev.c
    ===================================================================
    --- linux.orig/drivers/input/evdev.c
    +++ linux/drivers/input/evdev.c
    @@ -16,6 +16,7 @@
    #define EVDEV_BUF_PACKETS 8

    #include <linux/poll.h>
    +#include <linux/eventpoll.h>
    #include <linux/sched.h>
    #include <linux/slab.h>
    #include <linux/module.h>
    @@ -43,6 +44,7 @@ struct evdev_client {
    unsigned int tail;
    unsigned int packet_head; /* [future] position of the first element of next packet */
    spinlock_t buffer_lock; /* protects access to buffer, head and tail */
    + struct wakeup_source *wakeup_source;
    struct fasync_struct *fasync;
    struct evdev *evdev;
    struct list_head node;
    @@ -75,10 +77,12 @@ static void evdev_pass_event(struct evde
    client->buffer[client->tail].value = 0;

    client->packet_head = client->tail;
    + __pm_relax(client->wakeup_source);
    }

    if (event->type == EV_SYN && event->code == SYN_REPORT) {
    client->packet_head = client->head;
    + __pm_stay_awake(client->wakeup_source);
    kill_fasync(&client->fasync, SIGIO, POLL_IN);
    }

    @@ -255,6 +259,8 @@ static int evdev_release(struct inode *i
    mutex_unlock(&evdev->mutex);

    evdev_detach_client(evdev, client);
    + wakeup_source_unregister(client->wakeup_source);
    +
    kfree(client);

    evdev_close_device(evdev);
    @@ -373,6 +379,8 @@ static int evdev_fetch_next_event(struct
    if (have_event) {
    *event = client->buffer[client->tail++];
    client->tail &= client->bufsize - 1;
    + if (client->packet_head == client->tail)
    + __pm_relax(client->wakeup_source);
    }

    spin_unlock_irq(&client->buffer_lock);
    @@ -433,6 +441,52 @@ static unsigned int evdev_poll(struct fi
    return mask;
    }

    +static void evdev_client_attach_wakeup_source(struct evdev_client *client)
    +{
    + struct wakeup_source *ws;
    +
    + ws = wakeup_source_register(dev_name(&client->evdev->dev));
    + spin_lock_irq(&client->buffer_lock);
    + client->wakeup_source = ws;
    + if (client->packet_head != client->tail)
    + __pm_stay_awake(client->wakeup_source);
    + spin_unlock_irq(&client->buffer_lock);
    +}
    +
    +static void evdev_client_detach_wakeup_source(struct evdev_client *client)
    +{
    + struct wakeup_source *ws;
    +
    + spin_lock_irq(&client->buffer_lock);
    + ws = client->wakeup_source;
    + client->wakeup_source = NULL;
    + spin_unlock_irq(&client->buffer_lock);
    + wakeup_source_unregister(ws);
    +}
    +
    +static void evdev_epoll_ctl(struct file *file, int op,
    + unsigned int events)
    +{
    + struct evdev_client *client = file->private_data;
    +
    + switch (op) {
    + case EPOLL_CTL_ADD:
    + if ((events & EPOLLWAKEUP) && !client->wakeup_source)
    + evdev_client_attach_wakeup_source(client);
    + break;
    + case EPOLL_CTL_DEL:
    + if (events & EPOLLWAKEUP)
    + evdev_client_detach_wakeup_source(client);
    + break;
    + case EPOLL_CTL_MOD:
    + /* 'events' is the new events mask (after the change) */
    + if ((events & EPOLLWAKEUP) && !client->wakeup_source)
    + evdev_client_attach_wakeup_source(client);
    + else if (!(events & EPOLLWAKEUP))
    + evdev_client_detach_wakeup_source(client);
    + }
    +}
    +
    #ifdef CONFIG_COMPAT

    #define BITS_PER_LONG_COMPAT (sizeof(compat_long_t) * 8)
    @@ -845,6 +899,7 @@ static const struct file_operations evde
    .read = evdev_read,
    .write = evdev_write,
    .poll = evdev_poll,
    + .epoll_ctl = evdev_epoll_ctl,
    .open = evdev_open,
    .release = evdev_release,
    .unlocked_ioctl = evdev_ioctl,
    Index: linux/include/linux/eventpoll.h
    ===================================================================
    --- linux.orig/include/linux/eventpoll.h
    +++ linux/include/linux/eventpoll.h
    @@ -26,6 +26,12 @@
    #define EPOLL_CTL_DEL 2
    #define EPOLL_CTL_MOD 3

    +/*
    + * Request the handling of system wakeup events so as to prevent automatic
    + * system suspends from happening while those events are being processed.
    + */
    +#define EPOLLWAKEUP (1 << 29)
    +
    /* Set the One Shot behaviour for the target file descriptor */
    #define EPOLLONESHOT (1 << 30)

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