On 03/03/25 09:02, Denis OSTERLAND-HEIM wrote:
[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
Acked-by: Rodolfo Giometti giometti@enneenne.com
If needed. :)
Fixes: eae9d2ba0cfc ("LinuxPPS: core support") CC: stable@vger.linux.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 */
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 */
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 */