[PATCH 5.4 37/39] pwm: meson: Explicitly set .polarity in .get_state()

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

From: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>

commit 8caa81eb950cb2e9d2d6959b37d853162d197f57 upstream.

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@amazon.com>
Acked-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Link: https://lore.kernel.org/r/20230310191405.2606296-1-u.kleine-koenig@pengutronix.de
Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Thierry Reding <thierry.reding@gmail.com>
Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 drivers/pwm/pwm-meson.c |    7 +++++++
 1 file changed, 7 insertions(+)

--- a/drivers/pwm/pwm-meson.c
+++ b/drivers/pwm/pwm-meson.c
@@ -168,6 +168,12 @@ static int meson_pwm_calc(struct meson_p
 	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;
 
@@ -366,6 +372,7 @@ static void meson_pwm_get_state(struct p
 		state->period = 0;
 		state->duty_cycle = 0;
 	}
+	state->polarity = PWM_POLARITY_NORMAL;
 }
 
 static const struct pwm_ops meson_pwm_ops = {