Messages in this thread Patch in this message | | | Date | Fri, 2 Oct 2020 15:08:44 +0200 | From | Lars Poeschel <> | Subject | Re: [PATCH 1/2] pwm: sysfs: Set class on pwm devices |
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On Fri, Oct 02, 2020 at 02:46:16PM +0200, Greg Kroah-Hartman wrote: > On Fri, Oct 02, 2020 at 02:30:47PM +0200, poeschel@lemonage.de wrote: > > From: Lars Poeschel <poeschel@lemonage.de> > > > > This adds a class to exported pwm devices. > > Exporting a pwm through sysfs did not yield udev events. The > > dev_uevent_filter function does filter-out devices without a bus or > > class. > > This was already addressed in commit > > commit 7e5d1fd75c3d ("pwm: Set class for exported channels in sysfs") > > but this did cause problems and the commit got reverted with > > commit c289d6625237 ("Revert "pwm: Set class for exported channels in > > sysfs"") > > Problem with the previous approach was, that there is a clash if we have > > multiple pwmchips: > > echo 0 > pwmchip0/export > > echo 0 > pwmchip1/export > > would both export /sys/class/pwm/pwm0 . > > > > Now this patch changes the sysfs interface. We do include the pwmchip > > number into the pwm directory that gets exported. > > With the example above we get: > > /sys/class/pwm/pwm-0-0 > > /sys/class/pwm/pwm-1-0 > > We maintain ABI backward compatibility through symlinks. > > /sys/class/pwm/pwmchip0/pwm0 > > /sys/class/pwm/pwmchip1/pwm0 > > are now symbolic links to the new names. > > > > Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org> > > Signed-off-by: Lars Poeschel <poeschel@lemonage.de> > > --- > > drivers/pwm/sysfs.c | 57 +++++++++++++++++++++++++++++++++++++-------- > > 1 file changed, 47 insertions(+), 10 deletions(-) > > > > diff --git a/drivers/pwm/sysfs.c b/drivers/pwm/sysfs.c > > index 449dbc0f49ed..c708da17a857 100644 > > --- a/drivers/pwm/sysfs.c > > +++ b/drivers/pwm/sysfs.c > > @@ -240,8 +240,10 @@ static void pwm_export_release(struct device *child) > > > > static int pwm_export_child(struct device *parent, struct pwm_device *pwm) > > { > > + struct pwm_chip *chip = dev_get_drvdata(parent); > > struct pwm_export *export; > > char *pwm_prop[2]; > > + char *link_name; > > int ret; > > > > if (test_and_set_bit(PWMF_EXPORTED, &pwm->flags)) > > @@ -256,25 +258,39 @@ 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); > > export->child.groups = pwm_groups; > > - dev_set_name(&export->child, "pwm%u", pwm->hwpwm); > > + dev_set_name(&export->child, "pwm-%u-%u", chip->base, pwm->hwpwm); > > > > ret = device_register(&export->child); > > - if (ret) { > > - clear_bit(PWMF_EXPORTED, &pwm->flags); > > - put_device(&export->child); > > - export = NULL; > > - return ret; > > + if (ret) > > + goto error; > > + > > + link_name = kasprintf(GFP_KERNEL, "pwm%u", pwm->hwpwm); > > + if (link_name == NULL) { > > + ret = -ENOMEM; > > + goto dev_unregister; > > } > > - pwm_prop[0] = kasprintf(GFP_KERNEL, "EXPORT=pwm%u", pwm->hwpwm); > > + > > + pwm_prop[0] = kasprintf(GFP_KERNEL, "EXPORT=%s", > > + export->child.kobj.name); > > pwm_prop[1] = NULL; > > kobject_uevent_env(&parent->kobj, KOBJ_CHANGE, pwm_prop); > > Do you still need to do this by hand? Why can't this uevent field > belong to the class and have it create this for you automatically when > the device is added?
I did not add this with my patch, it was there before and I wonder, what purpose it served, since the uevent was filtered because there was no class there. Now we have a class and now it works and this is what happens:
/sys/class/pwm# echo 0 > pwmchip1/export KERNEL[2111.952725] add /devices/platform/ocp/48302000.epwmss/48302200.pwm/pwm/pwmchip1/pwm-1-0 (pwm) ACTION=add DEVPATH=/devices/platform/ocp/48302000.epwmss/48302200.pwm/pwm/pwmchip1/pwm-1-0 SEQNUM=1546 SUBSYSTEM=pwm
KERNEL[2111.955155] change /devices/platform/ocp/48302000.epwmss/48302200.pwm/pwm/pwmchip1 (pwm) ACTION=change DEVPATH=/devices/platform/ocp/48302000.epwmss/48302200.pwm/pwm/pwmchip1 EXPORT=pwm-1-0 SEQNUM=1547 SUBSYSTEM=pwm
The first event is the event from device_register. It informs us that we now have a new pwm-1-0. Nice. The second is the event done here "by hand". It informs us, that pwmchip1 changed. It has a new export now. For me personally this is not needed, but also I don't think it is wrong. You decide!
> > kfree(pwm_prop[0]); > > > > - return 0; > > + ret = sysfs_create_link(&parent->kobj, &export->child.kobj, link_name); > > You create the link _after_ you told userspace it was there, you raced > and lost :(
Are you sure ? We inform userspace that there is a "pwm-1-0" now available. We do not say anything about "pwm0". "pwm0" is the name of our symlink. This should not be a problem.
> > + return ret; > > + > > +dev_unregister: > > + device_unregister(&export->child); > > +error: > > + clear_bit(PWMF_EXPORTED, &pwm->flags); > > + put_device(&export->child); > > + export = NULL; > > + return ret; > > } > > > > static int pwm_unexport_match(struct device *child, void *data) > > @@ -286,6 +302,7 @@ static int pwm_unexport_child(struct device *parent, struct pwm_device *pwm) > > { > > struct device *child; > > char *pwm_prop[2]; > > + char *link_name; > > > > if (!test_and_clear_bit(PWMF_EXPORTED, &pwm->flags)) > > return -ENODEV; > > @@ -294,7 +311,11 @@ 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); > > + link_name = kasprintf(GFP_KERNEL, "pwm%u", pwm->hwpwm); > > + if (link_name) > > + sysfs_delete_link(&parent->kobj, &child->kobj, link_name); > > + > > + pwm_prop[0] = kasprintf(GFP_KERNEL, "UNEXPORT=%s", child->kobj.name); > > pwm_prop[1] = NULL; > > kobject_uevent_env(&parent->kobj, KOBJ_CHANGE, pwm_prop); > > Same uevent question here. > > Otherwise, this looks good, nice work in figuring out the is_visable > stuff and everything.
Thanks! :-) And thank you for your help so far.
Regards, Lars
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