From: Denis OSTERLAND-HEIM Date: Wed, 28 May 2025 10:57:50 +0000 (+0200) Subject: pps: fix poll support X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=12c409aa1ec2592280a2ddcc66ff8f3c7f7bb171;p=thirdparty%2Fkernel%2Fstable.git pps: fix poll support Because pps_cdev_poll() returns unconditionally EPOLLIN, a user space program that calls select/poll get always an immediate data ready-to-read response. As a result the intended use to wait until next data becomes ready does not work. User space snippet: struct pollfd pollfd = { .fd = open("/dev/pps0", O_RDONLY), .events = POLLIN|POLLERR, .revents = 0 }; while(1) { poll(&pollfd, 1, 2000/*ms*/); // returns immediate, but should wait if(revents & EPOLLIN) { // always true struct pps_fdata fdata; memset(&fdata, 0, sizeof(memdata)); ioctl(PPS_FETCH, &fdata); // currently fetches data at max speed } } Lets remember the last fetch event counter and compare this value in pps_cdev_poll() with most recent event counter and return 0 if they are equal. Signed-off-by: Denis OSTERLAND-HEIM Co-developed-by: Rodolfo Giometti Signed-off-by: Rodolfo Giometti Fixes: eae9d2ba0cfc ("LinuxPPS: core support") Link: https://lore.kernel.org/all/f6bed779-6d59-4f0f-8a59-b6312bd83b4e@enneenne.com/ Acked-by: Rodolfo Giometti Link: https://lore.kernel.org/r/c3c50ad1eb19ef553eca8a57c17f4c006413ab70.camel@gmail.com Signed-off-by: Greg Kroah-Hartman --- diff --git a/drivers/pps/pps.c b/drivers/pps/pps.c index 6a02245ea35f..9463232af8d2 100644 --- a/drivers/pps/pps.c +++ b/drivers/pps/pps.c @@ -41,6 +41,9 @@ static __poll_t pps_cdev_poll(struct file *file, poll_table *wait) poll_wait(file, &pps->queue, wait); + if (pps->last_fetched_ev == pps->last_ev) + return 0; + return EPOLLIN | EPOLLRDNORM; } @@ -186,9 +189,11 @@ static long pps_cdev_ioctl(struct file *file, if (err) return err; - /* Return the fetched timestamp */ + /* Return the fetched timestamp and save last fetched event */ spin_lock_irq(&pps->lock); + pps->last_fetched_ev = pps->last_ev; + fdata.info.assert_sequence = pps->assert_sequence; fdata.info.clear_sequence = pps->clear_sequence; fdata.info.assert_tu = pps->assert_tu; @@ -272,9 +277,11 @@ static long pps_cdev_compat_ioctl(struct file *file, if (err) return err; - /* Return the fetched timestamp */ + /* Return the fetched timestamp and save last fetched event */ spin_lock_irq(&pps->lock); + pps->last_fetched_ev = pps->last_ev; + compat.info.assert_sequence = pps->assert_sequence; compat.info.clear_sequence = pps->clear_sequence; compat.info.current_mode = pps->current_mode; diff --git a/include/linux/pps_kernel.h b/include/linux/pps_kernel.h index c7abce28ed29..aab0aebb529e 100644 --- a/include/linux/pps_kernel.h +++ b/include/linux/pps_kernel.h @@ -52,6 +52,7 @@ struct pps_device { int current_mode; /* PPS mode at event time */ unsigned int last_ev; /* last PPS event id */ + unsigned int last_fetched_ev; /* last fetched PPS event id */ wait_queue_head_t queue; /* PPS event queue */ unsigned int id; /* PPS source unique ID */