On Thu, Jan 07, 2021 at 01:50:53AM -0800, Prashant Malani wrote: > Hi Greg, > > Thanks for taking a look at the patch. > > On Thu, Jan 7, 2021 at 1:16 AM Greg KH <gregkh@xxxxxxxxxxxxxxxxxxx> wrote: > > > > On Wed, Jan 06, 2021 at 07:49:04PM -0800, Prashant Malani wrote: > > > Generate a change uevent when the "number_of_alternate_modes" sysfs file > > > for partners and plugs is updated by a port driver. > > > > > > Cc: Heikki Krogerus <heikki.krogerus@xxxxxxxxxxxxxxx> > > > Cc: Benson Leung <bleung@xxxxxxxxxxxx> > > > Signed-off-by: Prashant Malani <pmalani@xxxxxxxxxxxx> > > > --- > > > drivers/usb/typec/class.c | 2 ++ > > > 1 file changed, 2 insertions(+) > > > > > > diff --git a/drivers/usb/typec/class.c b/drivers/usb/typec/class.c > > > index ebfd3113a9a8..8f77669f9cf4 100644 > > > --- a/drivers/usb/typec/class.c > > > +++ b/drivers/usb/typec/class.c > > > @@ -766,6 +766,7 @@ int typec_partner_set_num_altmodes(struct typec_partner *partner, int num_altmod > > > return ret; > > > > > > sysfs_notify(&partner->dev.kobj, NULL, "number_of_alternate_modes"); > > > + kobject_uevent(&partner->dev.kobj, KOBJ_CHANGE); > > > > Shouldn't the sysfs_notify() handle the "something has changed" logic > > good enough for userspace, as obviously someone is polling on the thing > > (otherwise we wouldn't be calling sysfs_notify...) > > > > The kobject itself hasn't "changed", but rather an individual attribute > > has changed. We don't want to create uevents for every individual sysfs > > attribute changing values, do we? > > Fair point. I noticed other attributes in this source file use a > similar approach (sysfs_notify + kobject_uevent) > and took guidance from there in an attempt to remain consistent > (though, of course, your point still stands). > > I'm guessing it is for processes that rely on udev events > (subsystem=typec) rather than polling. > > > > > What is preventing a normal "monitor the sysfs file" logic from working > > here for anyone who wants to know that the alternate modes have changed? > > One limitation I can think of is that this sysfs file is hidden till > it has a valid value (i.e >= 0), so a user-space process might not > be able to poll on the file till it is visible (I suppose even then > one could poll on the parent). If the file is being added at this point in time, then yes, it is ok to send a KOBJ_CHANGE event as that is needed. Is that what is happening here? thanks, greg k-h
