pwm: Fix pwm_apply_args()

Commit 5ec803edcb70 ("pwm: Add core infrastructure to allow atomic
updates"), implemented pwm_disable() as a wrapper around
pwm_apply_state(), and then, commit ef2bf4997f7d ("pwm: Improve args
checking in pwm_apply_state()") added missing checks on the ->period
value in pwm_apply_state() to ensure we were not passing inappropriate
values to the ->config() or ->apply() methods.

The conjunction of these 2 commits led to a case where pwm_disable()
was no longer succeeding, thus preventing the polarity setting done
in pwm_apply_args().

Set a valid period in pwm_apply_args() to ensure polarity setting
won't be rejected.

Signed-off-by: Boris Brezillon <boris.brezillon@free-electrons.com>
Reported-by: Geert Uytterhoeven <geert@linux-m68k.org>
Suggested-by: Brian Norris <briannorris@chromium.org>
Fixes: 5ec803edcb70 ("pwm: Add core infrastructure to allow atomic updates")
Tested-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Brian Norris <briannorris@chromium.org>
Signed-off-by: Thierry Reding <thierry.reding@gmail.com>

include/linux/pwm.h

@@ -464,6 +464,8 @@ static inline bool pwm_can_sleep(struct pwm_device *pwm)
 
 static inline void pwm_apply_args(struct pwm_device *pwm)
 {
+	struct pwm_state state = { };
+
 	/*
 	 * PWM users calling pwm_apply_args() expect to have a fresh config
 	 * where the polarity and period are set according to pwm_args info.
@@ -476,18 +478,20 @@ static inline void pwm_apply_args(struct pwm_device *pwm)
 	 * at startup (even if they are actually enabled), thus authorizing
 	 * polarity setting.
 	 *
-	 * Instead of setting ->enabled to false, we call pwm_disable()
-	 * before pwm_set_polarity() to ensure that everything is configured
-	 * as expected, and the PWM is really disabled when the user request
-	 * it.
+	 * To fulfill this requirement, we apply a new state which disables
+	 * the PWM device and set the reference period and polarity config.
 	 *
 	 * Note that PWM users requiring a smooth handover between the
 	 * bootloader and the kernel (like critical regulators controlled by
 	 * PWM devices) will have to switch to the atomic API and avoid calling
 	 * pwm_apply_args().
 	 */
-	pwm_disable(pwm);
-	pwm_set_polarity(pwm, pwm->args.polarity);
+
+	state.enabled = false;
+	state.polarity = pwm->args.polarity;
+	state.period = pwm->args.period;
+
+	pwm_apply_state(pwm, &state);
 }
 
 struct pwm_lookup {