Messages in this thread | | | Subject | Re: [RESEND PATCH] Revert "pwm: Set class for exported channels in sysfs" | From | Fabrice Gasnier <> | Date | Tue, 25 Sep 2018 15:59:26 +0200 |
| |
On 09/24/2018 05:50 PM, Fabrice Gasnier wrote: > 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?
Hi Thierry,
Maybe there's a way around, keeping the revert patch, without impacting the ABI: - pwmX cannot be added to pwm/another class without issue as discussed (numbering isn't unique). - pwmchipN already belongs to pwm class.
I did some testing, trying to send uevent on the pwmX directly, without success: uevents are filtered as pwmX doesn't belong to a class.
Still, it is possible to send uevent (KOBJ_CHANGE) on pwmchipN device, to notify of a change, e.g. pwmX channel being exported/unexported.
I run following prototype (with revert patch).
static int pwm_export_child(struct device *parent, struct pwm_device *pwm) { + char *pwm_prop[2]; struct pwm_export *export; int ret; ... kfree(export); 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; }
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; ... 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() */
Then, I run a quick test:
# 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
# echo 0 > /sys/class/pwm/pwmchip4/export KERNEL[202.089676] change /devices/.../pwm/pwmchip4 (pwm) ACTION=change DEVPATH=/devices/.../pwm/pwmchip4 EXPORT=pwm0 SEQNUM=2046 SUBSYSTEM=pwm
Also unexport will report change events to userland:
# echo 0 > /sys/class/pwm/pwmchip0/unexport KERNEL[1691.112765] change /devices/.../pwm/pwmchip0 (pwm) ACTION=change DEVPATH=/devices/.../pwm/pwmchip0 SEQNUM=2047 SUBSYSTEM=pwm UNEXPORT=pwm0
Do you think this may be a way around? Please let me know if this may satisfy need for uevents.
Best regards, Fabrice > > And this link is added using dev_name(). So I doubt adding a new class > will change the current behavior. > >> >> Thierry >>
| |