Messages in this thread | | | Subject | Re: [RESEND PATCH] Revert "pwm: Set class for exported channels in sysfs" | From | Fabrice Gasnier <> | Date | Mon, 24 Sep 2018 17:50:48 +0200 |
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On 09/24/2018 04:23 PM, Thierry Reding wrote: > On Mon, Sep 24, 2018 at 03:59:03PM +0200, Fabrice Gasnier wrote: >> On 09/24/2018 01:53 PM, Thierry Reding wrote: >>> On Fri, Sep 21, 2018 at 04:02:47PM +0200, Fabrice Gasnier wrote: >>>> This reverts commit 7e5d1fd75c3dde9fc10c4472b9368089d1b81d00 as it causes >>>> regression with multiple pwm chip. It creates a new entry in >>>> '/sys/class/pwm' every time a 'pwmX' is exported with 'echo X > export': >>>> - 1st time export will create an entry in /sys/class/pwm/pwmX >>>> - when another export happens on another pwmchip, it can't be created >>>> (e.g. -EEXIST) >>>> >>>> This also changes existing ABI (Documentation/ABI/testing/sysfs-class-pwm): >>>> - pmwX should be there: /sys/class/pwm/pwmchipN/pwmX >>>> >>>> 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... >>>> >>>> Signed-off-by: Fabrice Gasnier <fabrice.gasnier@st.com> >>>> --- >>>> drivers/pwm/sysfs.c | 1 - >>>> 1 file changed, 1 deletion(-) >>> >>> Can we come up with an alternative that allows us to have both? We want >>> uevent and proper sysfs creation, or is that not possible? >> >> Hi Thierry, all, >> >> With current approach: >> - "export->child.class = parent->class" >> - ABI (e.g. "pwm%d") device name isn't unique with multiple pwm chip. >> I think this is not possible. >> >> Trying to think of an alternative... I just did a quick test, by >> changing device name, to take pwmchip into account: >> + 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, "pwmchip%d-pwm%u", chip->base, >> pwm->hwpwm); >> >> But this also impacts existing ABI :-( >> Would you have suggestions to send an uevent, without modifying ABI ? > > I don't quite understand why, in the example you show in the commit > message, the pwmX nodes appear in the top-level /sys/class/pwm > directory. According to Documentation/ABI/testing/sysfs-class-pwm they > should appear as /sys/class/pwm/pwmchipN/pwmX. I can only imagine that > setting the class may have changed that.
Yes, adding the class makes the link to be created under /sys/class/pwm: device_register() -> device_add() -> device_add_class_symlinks() In device_add_class_symlinks(): ... if (!dev->class) return 0; ... /* link in the class directory pointing to the device */ error = sysfs_create_link(&dev->class->p->subsys.kobj, &dev->kobj, dev_name(dev)); ...
> If so, perhaps we can > workaround that by creating a new class that is not parent->class?
And this link is added using dev_name(). So I doubt adding a new class will change the current behavior.
> > Thierry >
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