[PATCH v5 2/4] pps: clients: gpio: only tear down the echo timer when it exists

[Eliav Farber <farbere@amazon.com>]

remove() calls timer_delete_sync() on data->echo_timer unconditionally,
but the timer is only initialised by timer_setup() in probe() when the
board describes an "echo" GPIO. On a board without echo-gpios the timer is
never set up, so remove() operates on a timer_list that was never
initialised.

The guard used to be there: it was dropped by commit fde046a8c490 ("pps:
clients: gpio: Remove redundant condition in ->remove()") on the grounds
that "the timer along with GPIO API are NULL-aware". That is true for the
GPIO API - gpiod_set_value() is a no-op for a NULL descriptor - but not
for the timer: timer_delete_sync() on a timer that was never timer_setup()
initialised trips the debug_assert_init() check and emits a debugobjects
"not initialized" warning under CONFIG_DEBUG_OBJECTS_TIMERS.

Restore the data->echo_pin guard around the echo teardown, mirroring the
condition under which the timer is set up in probe(). gpiod_set_value() is
kept under the same guard as it only makes sense together with the echo
timer.

Fixes: fde046a8c490 ("pps: clients: gpio: Remove redundant condition in ->remove()")
Signed-off-by: Eliav Farber <farbere@amazon.com>
---
Changes in v5:
- New patch. Split out because patch 4 mirrors remove()'s teardown in the
  new shutdown(); guarding the echo teardown here first keeps that latent
  issue out of both paths (Rodolfo Giometti)

 drivers/pps/clients/pps-gpio.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/drivers/pps/clients/pps-gpio.c b/drivers/pps/clients/pps-gpio.c
index ccc2fb470b7e..aec534c246af 100644
--- a/drivers/pps/clients/pps-gpio.c
+++ b/drivers/pps/clients/pps-gpio.c
@@ -211,9 +211,11 @@ static void pps_gpio_remove(struct platform_device *pdev)
 
 	free_irq(data->irq, data);
 	pps_unregister_source(data->pps);
-	timer_delete_sync(&data->echo_timer);
-	/* reset echo pin in any case */
-	gpiod_set_value(data->echo_pin, 0);
+	/* reset the echo state, if the board has an echo GPIO */
+	if (data->echo_pin) {
+		timer_delete_sync(&data->echo_timer);
+		gpiod_set_value(data->echo_pin, 0);
+	}
 	dev_info(&pdev->dev, "removed IRQ %d as PPS source\n", data->irq);
 }
 
-- 
2.47.3