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From:   Fabrice Gasnier <fabrice.gasnier@st.com>
To:     <thierry.reding@gmail.com>, <gottfried.haider@gmail.com>
CC:     <stefan.wahren@i2se.com>, <hsweeten@visionengravers.com>,
        <loic.pallardy@st.com>, <broonie@kernel.org>,
        <fabrice.gasnier@st.com>, <gohai@sukzessiv.net>,
        <michal.vokac@ysoft.com>,
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        <linux-arm-kernel@lists.infradead.org>,
        <linux-rpi-kernel@lists.infradead.org>,
        <linux-kernel@vger.kernel.org>, <linux-pwm@vger.kernel.org>
Subject: [PATCH v2 1/2] Revert "pwm: Set class for exported channels in sysfs"
Date:   Mon, 1 Oct 2018 15:23:56 +0200
Message-ID: <1538400237-28766-2-git-send-email-fabrice.gasnier@st.com>
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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@st.com>
Tested-by: Gottfried Haider <gottfried.haider@gmail.com>
---
 drivers/pwm/sysfs.c | 1 -
 1 file changed, 1 deletion(-)

diff --git a/drivers/pwm/sysfs.c b/drivers/pwm/sysfs.c
index 7c71cdb..4726d43 100644
--- a/drivers/pwm/sysfs.c
+++ b/drivers/pwm/sysfs.c
@@ -263,7 +263,6 @@ static int pwm_export_child(struct device *parent, struct pwm_device *pwm)
 	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);
-- 
1.9.1