[PATCH 5.4 26/50] pwm: mxs: Dont modify HW state in .probe() after the PWM chip was registered

From: Greg Kroah-Hartman
Date: Fri Sep 24 2021 - 08:54:20 EST

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

commit 020162d6f49f2963062229814a56a89c86cbeaa8 upstream.

This fixes a race condition: After pwmchip_add() is called there might
already be a consumer and then modifying the hardware behind the
consumer's back is bad. So reset before calling pwmchip_add().

Note that reseting the hardware isn't the right thing to do if the PWM
is already running as it might e.g. disable (or even enable) a backlight
that is supposed to be on (or off).

Fixes: 4dce82c1e840 ("pwm: add pwm-mxs support")
Cc: Sascha Hauer <s.hauer@xxxxxxxxxxxxxx>
Cc: Shawn Guo <shawnguo@xxxxxxxxxx>
Signed-off-by: Uwe Kleine-König <u.kleine-koenig@xxxxxxxxxxxxxx>
Signed-off-by: Thierry Reding <thierry.reding@xxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
drivers/pwm/pwm-mxs.c | 13 +++++--------
1 file changed, 5 insertions(+), 8 deletions(-)

--- a/drivers/pwm/pwm-mxs.c
+++ b/drivers/pwm/pwm-mxs.c
@@ -150,6 +150,11 @@ static int mxs_pwm_probe(struct platform
return ret;

+ /* FIXME: Only do this if the PWM isn't already running */
+ ret = stmp_reset_block(mxs->base);
+ if (ret)
+ return dev_err_probe(&pdev->dev, ret, "failed to reset PWM\n");
ret = pwmchip_add(&mxs->chip);
if (ret < 0) {
dev_err(&pdev->dev, "failed to add pwm chip %d\n", ret);
@@ -158,15 +163,7 @@ static int mxs_pwm_probe(struct platform

platform_set_drvdata(pdev, mxs);

- ret = stmp_reset_block(mxs->base);
- if (ret)
- goto pwm_remove;
return 0;
- pwmchip_remove(&mxs->chip);
- return ret;

static int mxs_pwm_remove(struct platform_device *pdev)