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Subject[PATCH 4.19 08/85] Revert "pwm: Set class for exported channels in sysfs"
From: Fabrice Gasnier <>

commit c289d6625237aa785b484b4e94c23b3b91ea7e60 upstream.

This reverts commit 7e5d1fd75c3dde9fc10c4472b9368089d1b81d00 ("pwm: Set
class for exported channels in sysfs") as it causes regression with
multiple pwm chip[1], when exporting a pwm channel (echo X > export):

- ABI (Documentation/ABI/testing/sysfs-class-pwm) states pwmX should be
created in /sys/class/pwm/pwmchipN/pwmX
- Reverted patch causes new entry to be also created directly in
- 1st time, exporting pwmX will create an entry in /sys/class/pwm/pwmX
- class attributes are added under pwmX folder, such as export, unexport
npwm, symlinks. This is wrong as it belongs to pwmchipN. It may cause
bad behavior and report wrong values.
- when another export happens on another pwmchip, it can't be created
(e.g. -EEXIST). This is causing the issue with multiple pwmchip.

Example on stm32 (stm32429i-eval) platform:
$ ls /sys/class/pwm
pwmchip0 pwmchip4

$ cd /sys/class/pwm/pwmchip0/
$ echo 0 > export
$ ls /sys/class/pwm
pwm0 pwmchip0 pwmchip4

$ cd /sys/class/pwm/pwmchip4/
$ echo 0 > export
sysfs: cannot create duplicate filename '/class/pwm/pwm0'
...Exception stack follows...

This is also seen on other platform [2]


Signed-off-by: Fabrice Gasnier <>
Tested-by: Gottfried Haider <>
Tested-by: Michal Vokáč <>
Signed-off-by: Thierry Reding <>
Cc: John Keeping <>
Signed-off-by: Greg Kroah-Hartman <>

drivers/pwm/sysfs.c | 1 -
1 file changed, 1 deletion(-)

--- a/drivers/pwm/sysfs.c
+++ b/drivers/pwm/sysfs.c
@@ -263,7 +263,6 @@ static int pwm_export_child(struct devic
export->pwm = pwm;

- export->child.class = parent->class;
export->child.release = pwm_export_release;
export->child.parent = parent;
export->child.devt = MKDEV(0, 0);

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