[PATCH v3] backlight: pwm_bl: Disable PWM on shutdown and suspend

[Uwe Kleine-König]

Since commit 00e7e698bff1 ("backlight: pwm_bl: Configure pwm only once
per backlight toggle") calling pwm_backlight_power_off() doesn't disable
the PWM any more. However this is necessary to suspend because PWM
drivers usually refuse to suspend if they are still enabled.

Also adapt shutdown and remove callbacks to disable the PWM for similar
reasons.

Fixes: 00e7e698bff1 ("backlight: pwm_bl: Configure pwm only once per backlight toggle")
Reported-by: Aisheng Dong <aisheng.dong at nxp.com>
Tested-by: Aisheng Dong <aisheng.dong at nxp.com>
Signed-off-by: Uwe Kleine-König <u.kleine-koenig at pengutronix.de>
---
Hello,

On Tue, Sep 26, 2023 at 12:11:37PM +0100, Daniel Thompson wrote:
> Changes proposed look good (and the comment about badly designed boards
> going to HiZ state we super helpful).

I didn't mention Hi-Z and note that disabling a PWM can even result in
the hardware driving to the active level. (This can happen for example
for pwm-mxs and pwm-imx27.)

> Only thing from my is why there is no attempt to disable the PWM
> from the .remove_new() callback.

Good catch, good I didn't manage to send out a v3 for the email address
fix yet :-) So here comes a v3 with two improvments:

Changes since v2
(https://lore.kernel.org/dri-devel/20230926084612.2074692-1-u.kleine-koenig@pengutronix.de):

 - Fix Aisheng Dong's email address
 - also disable PWM in .remove and adapt commit log accordingly (Thanks
   to Daniel Thompson for spotting that).

 drivers/video/backlight/pwm_bl.c | 21 +++++++++++++++++++++
 1 file changed, 21 insertions(+)

diff --git a/drivers/video/backlight/pwm_bl.c b/drivers/video/backlight/pwm_bl.c
index a51fbab96368..390398ae07b9 100644
--- a/drivers/video/backlight/pwm_bl.c
+++ b/drivers/video/backlight/pwm_bl.c
@@ -629,6 +629,10 @@ static void pwm_backlight_remove(struct platform_device *pdev)
 
 	backlight_device_unregister(bl);
 	pwm_backlight_power_off(pb);
+	pwm_get_state(pb->pwm, &state);
+	state.duty_cycle = 0;
+	state.enabled = false;
+	pwm_apply_state(pb->pwm, &state);
 
 	if (pb->exit)
 		pb->exit(&pdev->dev);
@@ -638,8 +642,13 @@ static void pwm_backlight_shutdown(struct platform_device *pdev)
 {
 	struct backlight_device *bl = platform_get_drvdata(pdev);
 	struct pwm_bl_data *pb = bl_get_data(bl);
+	struct pwm_state state;
 
 	pwm_backlight_power_off(pb);
+	pwm_get_state(pb->pwm, &state);
+	state.duty_cycle = 0;
+	state.enabled = false;
+	pwm_apply_state(pb->pwm, &state);
 }
 
 #ifdef CONFIG_PM_SLEEP
@@ -647,12 +656,24 @@ static int pwm_backlight_suspend(struct device *dev)
 {
 	struct backlight_device *bl = dev_get_drvdata(dev);
 	struct pwm_bl_data *pb = bl_get_data(bl);
+	struct pwm_state state;
 
 	if (pb->notify)
 		pb->notify(pb->dev, 0);
 
 	pwm_backlight_power_off(pb);
 
+	/*
+	 * Note that disabling the PWM doesn't guarantee that the output stays
+	 * at its inactive state. However without the PWM disabled, the PWM
+	 * driver refuses to suspend. So disable here even though this might
+	 * enable the backlight on poorly designed boards.
+	 */
+	pwm_get_state(pb->pwm, &state);
+	state.duty_cycle = 0;
+	state.enabled = false;
+	pwm_apply_state(pb->pwm, &state);
+
 	if (pb->notify_after)
 		pb->notify_after(pb->dev, 0);
 

base-commit: 8fff9184d1b5810dca5dd1a02726d4f844af88fc
-- 
2.40.1