[BUG] 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 } }
[CAUSE] pps_cdev_poll() returns unconditionally EPOLLIN.
[FIX] 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 denis.osterland@diehl.com Co-developed-by: Rodolfo Giometti giometti@enneenne.com Signed-off-by: Rodolfo Giometti giometti@enneenne.com Fixes: eae9d2ba0cfc ("LinuxPPS: core support") CC: stable@vger.kernel.org # 5.4+ --- drivers/pps/pps.c | 11 +++++++++-- include/linux/pps_kernel.h | 1 + 2 files changed, 10 insertions(+), 2 deletions(-)
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 */ -- 2.47.2 Diehl Metering GmbH, Donaustrasse 120, 90451 Nuernberg Sitz der Gesellschaft: Ansbach, Registergericht: Ansbach HRB 69 Geschaeftsfuehrer: Dr. Christof Bosbach (Sprecher), Dipl.-Dolm. Annette Geuther, Dipl.-Kfm. Reiner Edel, Jean-Claude Luttringer
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