From 93781560b2fdd26fa8499d64db8a95a07e1dc902 Mon Sep 17 00:00:00 2001 From: Michael Byczkowski Date: Mon, 1 Jun 2026 17:44:09 -0700 Subject: [PATCH] pps: pps-gpio: split IRQ handler into hardirq timestamper + threaded handler Split the pps-gpio interrupt handler into a primary (hardirq) handler that captures the PPS timestamp at interrupt entry, and a threaded handler that processes the event. This produces the same two-part handler structure on both PREEMPT_RT and non-RT kernels. On non-RT kernels the threaded portion runs immediately after the primary, with no behavioral change compared to the previous single-handler implementation. On PREEMPT_RT, where interrupt handlers are force-threaded by default, the previous single-handler implementation captured the timestamp inside the threaded portion, after IRQ-thread scheduling delay. With the split, the timestamp is captured in true hardirq context as it is on non-RT kernels, eliminating a significant source of PPS jitter on RT systems. Link: https://lore.kernel.org/2e32729029fbf6977ecf04665eb00f2efd3e2c17.1780359378.git.calvin@wbinvd.org Signed-off-by: Michael Byczkowski Signed-off-by: Calvin Owens Reviewed-by: Sebastian Andrzej Siewior Tested-by: Michael Byczkowski Tested-by: Calvin Owens Acked-by: Rodolfo Giometti Signed-off-by: Andrew Morton --- drivers/pps/clients/pps-gpio.c | 39 ++++++++++++++++++++++------------ 1 file changed, 26 insertions(+), 13 deletions(-) diff --git a/drivers/pps/clients/pps-gpio.c b/drivers/pps/clients/pps-gpio.c index 402f910f3e25..7d87481280b2 100644 --- a/drivers/pps/clients/pps-gpio.c +++ b/drivers/pps/clients/pps-gpio.c @@ -34,33 +34,44 @@ struct pps_gpio_device_data { bool capture_clear; unsigned int echo_active_ms; /* PPS echo active duration */ unsigned long echo_timeout; /* timer timeout value in jiffies */ + struct pps_event_time ts; /* timestamp captured in hardirq */ }; /* * Report the PPS event */ -static irqreturn_t pps_gpio_irq_handler(int irq, void *data) +/* + * Primary hardirq handler -- runs in hardirq context even on PREEMPT_RT. + * Only captures the timestamp; all other work is deferred to the thread. + */ +static irqreturn_t pps_gpio_irq_hardirq(int irq, void *data) { - const struct pps_gpio_device_data *info; - struct pps_event_time ts; + struct pps_gpio_device_data *info = data; + + pps_get_ts(&info->ts); + + return IRQ_WAKE_THREAD; +} + +/* + * Threaded handler -- processes the PPS event using the timestamp + * captured in hardirq context above. + */ +static irqreturn_t pps_gpio_irq_thread(int irq, void *data) +{ + struct pps_gpio_device_data *info = data; int rising_edge; - /* Get the time stamp first */ - pps_get_ts(&ts); - - info = data; - - /* Small trick to bypass the check on edge's direction when capture_clear is unset */ rising_edge = info->capture_clear ? gpiod_get_value(info->gpio_pin) : !info->assert_falling_edge; if ((rising_edge && !info->assert_falling_edge) || (!rising_edge && info->assert_falling_edge)) - pps_event(info->pps, &ts, PPS_CAPTUREASSERT, data); + pps_event(info->pps, &info->ts, PPS_CAPTUREASSERT, data); else if (info->capture_clear && ((rising_edge && info->assert_falling_edge) || (!rising_edge && !info->assert_falling_edge))) - pps_event(info->pps, &ts, PPS_CAPTURECLEAR, data); + pps_event(info->pps, &info->ts, PPS_CAPTURECLEAR, data); else dev_warn_ratelimited(&info->pps->dev, "IRQ did not trigger any PPS event\n"); @@ -209,8 +220,10 @@ static int pps_gpio_probe(struct platform_device *pdev) } /* register IRQ interrupt handler */ - ret = request_irq(data->irq, pps_gpio_irq_handler, - get_irqf_trigger_flags(data), data->info.name, data); + ret = request_threaded_irq(data->irq, + pps_gpio_irq_hardirq, pps_gpio_irq_thread, + get_irqf_trigger_flags(data) | IRQF_ONESHOT, + data->info.name, data); if (ret) { pps_unregister_source(data->pps); dev_err(dev, "failed to acquire IRQ %d\n", data->irq);