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pps: pps-gpio: split IRQ handler into hardirq timestamper + threaded handler

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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 <by@by-online.de>
Signed-off-by: Calvin Owens <calvin@wbinvd.org>
Reviewed-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Tested-by: Michael Byczkowski <by@by-online.de>
Tested-by: Calvin Owens <calvin@wbinvd.org>
Acked-by: Rodolfo Giometti <giometti@enneenne.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Michael Byczkowski
2026-06-01 17:44:09 -07:00
committed by Andrew Morton
parent 8fdcbb5b37
commit 93781560b2
1 changed files with 26 additions and 13 deletions
Download Patch File Download Diff File Expand all files Collapse all files

39
drivers/pps/clients/pps-gpio.c
View File

@@ -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);