5.15-stable review patch. If anyone has any objections, please let me know.
------------------
From: Michael Byczkowski <redacted>
[ Upstream commit 93781560b2fdd26fa8499d64db8a95a07e1dc902 ]
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 (local)
Signed-off-by: Michael Byczkowski <redacted>
Signed-off-by: Calvin Owens <redacted>
Reviewed-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Tested-by: Michael Byczkowski <redacted>
Tested-by: Calvin Owens <redacted>
Acked-by: Rodolfo Giometti <giometti@enneenne.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Stable-dep-of: b899e0279f90 ("pps-gpio: remove dead capture_clear code")
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
drivers/pps/clients/pps-gpio.c | 37 +++++++++++++++++++++++-----------
1 file changed, 25 insertions(+), 12 deletions(-)
diff --git a/drivers/pps/clients/pps-gpio.c b/drivers/pps/clients/pps-gpio.c
index dbe598d092099..d21fc4bf0e3df 100644
--- a/drivers/pps/clients/pps-gpio.c
+++ b/drivers/pps/clients/pps-gpio.c
@@ -35,33 +35,44 @@ 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;
- int rising_edge;
+ struct pps_gpio_device_data *info = data;
+
+ pps_get_ts(&info->ts);
- /* Get the time stamp first */
- pps_get_ts(&ts);
+ return IRQ_WAKE_THREAD;
+}
- info = data;
+/*
+ * 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;
- /* 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");
@@ -210,8 +221,10 @@ 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);--
2.53.0