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

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Message-ID: <20250108153012.514925-1-bastien.curutchet@bootlin.com>
Date: Wed,  8 Jan 2025 16:30:12 +0100
From: Bastien Curutchet <bastien.curutchet@...tlin.com>
To: Rodolfo Giometti <giometti@...eenne.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc: linux-kernel@...r.kernel.org,
	Thomas Petazzoni <thomas.petazzoni@...tlin.com>,
	Herve Codina <herve.codina@...tlin.com>,
	Christopher Cordahi <christophercordahi@...ometrics.ca>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Bastien Curutchet <bastien.curutchet@...tlin.com>
Subject: [PATCH v4 1/1] pps: clients: gpio: Bypass edge's direction check when not needed

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@...tlin.com>
Acked-by: Rodolfo Giometti <giometti@...eenne.com>
---
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