[PATCH] pwm: meson: Explicitly set .polarity in .get_state()

[Uwe Kleine-König]

The driver only supports normal polarity. Complete the implementation of
.get_state() by setting .polarity accordingly.

This fixes a regression that was possible since commit c73a3107624d
("pwm: Handle .get_state() failures") which stopped to zero-initialize
the state passed to the .get_state() callback. This was reported at
https://forum.odroid.com/viewtopic.php?f=177&t=46360 . While this was an
unintended side effect, the real issue is the driver's callback not
setting the polarity.

There is a complicating fact, that the .apply() callback fakes support
for inversed polarity. This is not (and cannot) be matched by
.get_state(). As fixing this isn't easy, only point it out in a comment
to prevent authors of other drivers from copying that approach.

Fixes: c375bcbaabdb ("pwm: meson: Read the full hardware state in meson_pwm_get_state()")
Reported-by: Munehisa Kamata <kamatam at amazon.com>
Signed-off-by: Uwe Kleine-König <u.kleine-koenig at pengutronix.de>
---
Hello,

similar to the patches for four other drivers[1], I think we should
apply this patch as a fix.

Best regards
Uwe

[1] https://lore.kernel.org/linux-pwm/20230228135508.1798428-1-u.kleine-koenig@pengutronix.de

 drivers/pwm/pwm-meson.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/drivers/pwm/pwm-meson.c b/drivers/pwm/pwm-meson.c
index 16d79ca5d8f5..5cd7b90872c6 100644
--- a/drivers/pwm/pwm-meson.c
+++ b/drivers/pwm/pwm-meson.c
@@ -162,6 +162,12 @@ static int meson_pwm_calc(struct meson_pwm *meson, struct pwm_device *pwm,
 	duty = state->duty_cycle;
 	period = state->period;
 
+	/*
+	 * Note this is wrong. The result is an output wave that isn't really
+	 * inverted and so is wrongly identified by .get_state as normal.
+	 * Fixing this needs some care however as some machines might rely on
+	 * this.
+	 */
 	if (state->polarity == PWM_POLARITY_INVERSED)
 		duty = period - duty;
 
@@ -358,6 +364,8 @@ static int meson_pwm_get_state(struct pwm_chip *chip, struct pwm_device *pwm,
 		state->duty_cycle = 0;
 	}
 
+	state->polarity = PWM_POLARITY_NORMAL;
+
 	return 0;
 }
 
-- 
2.39.1