linux-kernel - [PATCH 4.19 08/85] Revert "pwm: Set class for exported channels in sysfs"

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Message-Id: <20190822171731.369519312@linuxfoundation.org>
Date:   Thu, 22 Aug 2019 10:18:41 -0700
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Fabrice Gasnier <fabrice.gasnier@...com>,
        Gottfried Haider <gottfried.haider@...il.com>,
        Michal Vokáč <michal.vokac@...ft.com>,
        Thierry Reding <thierry.reding@...il.com>,
        John Keeping <john@...anate.com>
Subject: [PATCH 4.19 08/85] Revert "pwm: Set class for exported channels in sysfs"

From: Fabrice Gasnier <fabrice.gasnier@...com>

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
  /sys/class/pwm/pwmX
- 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]

[1] https://lkml.org/lkml/2018/9/25/713
[2] https://lkml.org/lkml/2018/9/25/447

Signed-off-by: Fabrice Gasnier <fabrice.gasnier@...com>
Tested-by: Gottfried Haider <gottfried.haider@...il.com>
Tested-by: Michal Vokáč <michal.vokac@...ft.com>
Signed-off-by: Thierry Reding <thierry.reding@...il.com>
Cc: John Keeping <john@...anate.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

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