[PATCH v4 1/1] pps: clients: gpio: Bypass edge's direction check when not needed

[Bastien Curutchet]

In the IRQ handler, the GPIO's state is read to verify the direction of
the edge that triggered the interruption before generating the PPS event.
If a pulse is too short, the GPIO line can reach back its original state
before this verification and the PPS event is lost.

This check is needed when info->capture_clear is set because it needs
interruptions on both rising and falling edges. When info->capture_clear
is not set, interruption is triggered by one edge only so this check can
be omitted.

Add a warning if irq_handler is left without triggering any PPS event.
Bypass the edge's direction verification when info->capture_clear is not
set.

Signed-off-by: Bastien Curutchet <bastien.curutchet@xxxxxxxxxxx>
Acked-by: Rodolfo Giometti <giometti@xxxxxxxxxxxx>
---
Hi all,

This iteration is based on commit df7b2f206a9e in the branch
misc-test/char-misc-testing of
https://git.kernel.org/pub/scm/linux/kernel/git/gregkh/char-misc.git

Changes in v4:
 - Fix build error as pps->dev hasn't been a pointer since commit
   c79a39dc8d060 ("pps: Fix a use-after-free")
Changes in v3:
 - Add a warning in irq_handler
Changes in v2:
 - Modifiy the way the bypass is done to avoid code duplication
---
 drivers/pps/clients/pps-gpio.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/drivers/pps/clients/pps-gpio.c b/drivers/pps/clients/pps-gpio.c
index f77b19884f05..75c1bae30a7c 100644
--- a/drivers/pps/clients/pps-gpio.c
+++ b/drivers/pps/clients/pps-gpio.c
@@ -52,7 +52,9 @@ static irqreturn_t pps_gpio_irq_handler(int irq, void *data)
 
 	info = data;
 
-	rising_edge = gpiod_get_value(info->gpio_pin);
+	/* 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);
@@ -60,6 +62,8 @@ static irqreturn_t pps_gpio_irq_handler(int irq, void *data)
 			((rising_edge && info->assert_falling_edge) ||
 			(!rising_edge && !info->assert_falling_edge)))
 		pps_event(info->pps, &ts, PPS_CAPTURECLEAR, data);
+	else
+		dev_warn_ratelimited(&info->pps->dev, "IRQ did not trigger any PPS event\n");
 
 	return IRQ_HANDLED;
 }
-- 
2.47.1