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[2003:da:670f:9b00:eea2:32a1:2c09:46eb]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-45072559736sm13940965e9.19.2025.05.28.03.57.51 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 28 May 2025 03:57:51 -0700 (PDT) Message-ID: Subject: [PATCH v2] pps: fix poll support From: Denis Osterland-Heim To: Rodolfo Giometti , Andrew Morton , Greg Kroah-Hartman Cc: linux-kernel@vger.kernel.org, Denis OSTERLAND-HEIM Date: Wed, 28 May 2025 12:57:50 +0200 User-Agent: Evolution 3.56.0-1 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" From: Denis OSTERLAND-HEIM 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 =3D { .fd =3D open("/dev/pps0", O_RDONLY), .events =3D POLLIN|POLLERR, .revents =3D 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@enne= enne.com/ --- 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_tab= le *wait) =20 poll_wait(file, &pps->queue, wait); =20 + if (pps->last_fetched_ev =3D=3D pps->last_ev) + return 0; + return EPOLLIN | EPOLLRDNORM; } =20 @@ -186,9 +189,11 @@ static long pps_cdev_ioctl(struct file *file, if (err) return err; =20 - /* Return the fetched timestamp */ + /* Return the fetched timestamp and save last fetched event */ spin_lock_irq(&pps->lock); =20 + pps->last_fetched_ev =3D pps->last_ev; + fdata.info.assert_sequence =3D pps->assert_sequence; fdata.info.clear_sequence =3D pps->clear_sequence; fdata.info.assert_tu =3D pps->assert_tu; @@ -272,9 +277,11 @@ static long pps_cdev_compat_ioctl(struct file *file, if (err) return err; =20 - /* Return the fetched timestamp */ + /* Return the fetched timestamp and save last fetched event */ spin_lock_irq(&pps->lock); =20 + pps->last_fetched_ev =3D pps->last_ev; + compat.info.assert_sequence =3D pps->assert_sequence; compat.info.clear_sequence =3D pps->clear_sequence; compat.info.current_mode =3D 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 */ =20 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 */ =20 unsigned int id; /* PPS source unique ID */ --=20 2.48.1