[PATCH v2 2/2] pwm: send a uevent on the pwmchip device upon channel sysfs (un)export

[Fabrice Gasnier]

This patch sends a uevent (KOBJ_CHANGE) on the pwmchipN device, everytime
a pwmX channel has been exported/unexported via sysfs.
This allows udev to implement rules on such events, like:

SUBSYSTEM=="pwm*", PROGRAM="/bin/sh -c '\
        chown -R root:gpio /sys/class/pwm && chmod -R 770 /sys/class/pwm;\
        chown -R root:gpio
/sys/devices/platform/soc/*.pwm/pwm/pwmchip* && chmod -R 770
/sys/devices/platform/soc/*.pwm/pwm/pwmchip*\
'"

This is a replacement patch for commit 7e5d1fd75c3d ("pwm: Set class for
exported channels in sysfs"), see [1].

basic testing:
$ udevadm monitor --environment &
$ echo 0 > /sys/class/pwm/pwmchip0/export
KERNEL[197.321736] change   /devices/.../pwm/pwmchip0 (pwm)
ACTION=change
DEVPATH=/devices/.../pwm/pwmchip0
EXPORT=pwm0
SEQNUM=2045
SUBSYSTEM=pwm

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

Signed-off-by: Fabrice Gasnier <fabrice.gasn...@st.com>
Tested-by: Gottfried Haider <gottfried.hai...@gmail.com>
---
 drivers/pwm/sysfs.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/drivers/pwm/sysfs.c b/drivers/pwm/sysfs.c
index 4726d43..ceb233d 100644
--- a/drivers/pwm/sysfs.c
+++ b/drivers/pwm/sysfs.c
@@ -249,6 +249,7 @@ static void pwm_export_release(struct device *child)
 static int pwm_export_child(struct device *parent, struct pwm_device *pwm)
 {
        struct pwm_export *export;
+       char *pwm_prop[2];
        int ret;
 
        if (test_and_set_bit(PWMF_EXPORTED, &pwm->flags))
@@ -276,6 +277,10 @@ static int pwm_export_child(struct device *parent, struct 
pwm_device *pwm)
                export = NULL;
                return ret;
        }
+       pwm_prop[0] = kasprintf(GFP_KERNEL, "EXPORT=pwm%u", pwm->hwpwm);
+       pwm_prop[1] = NULL;
+       kobject_uevent_env(&parent->kobj, KOBJ_CHANGE, pwm_prop);
+       kfree(pwm_prop[0]);
 
        return 0;
 }
@@ -288,6 +293,7 @@ static int pwm_unexport_match(struct device *child, void 
*data)
 static int pwm_unexport_child(struct device *parent, struct pwm_device *pwm)
 {
        struct device *child;
+       char *pwm_prop[2];
 
        if (!test_and_clear_bit(PWMF_EXPORTED, &pwm->flags))
                return -ENODEV;
@@ -296,6 +302,11 @@ static int pwm_unexport_child(struct device *parent, 
struct pwm_device *pwm)
        if (!child)
                return -ENODEV;
 
+       pwm_prop[0] = kasprintf(GFP_KERNEL, "UNEXPORT=pwm%u", pwm->hwpwm);
+       pwm_prop[1] = NULL;
+       kobject_uevent_env(&parent->kobj, KOBJ_CHANGE, pwm_prop);
+       kfree(pwm_prop[0]);
+
        /* for device_find_child() */
        put_device(child);
        device_unregister(child);
-- 
1.9.1