[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@xxxxxxxxx>
Co-developed-by: Rodolfo Giometti <giometti@xxxxxxxxxxxx>
Signed-off-by: Rodolfo Giometti <giometti@xxxxxxxxxxxx>
Fixes: eae9d2ba0cfc ("LinuxPPS: core support")
CC: stable@xxxxxxxxxxxxxxx # 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
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