On Tue, Dec 08, 2020 at 03:45:19PM -0800, Prashant Malani wrote:
> Hi Heikki,
>
> Thanks a lot for looking at the patch.
>
> On Tue, Dec 8, 2020 at 1:37 AM Heikki Krogerus <heikki.krogerus@xxxxxxxxxxxxxxx> wrote:
> >
> > On Wed, Dec 02, 2020 at 07:08:47PM -0800, Prashant Malani wrote:
> > > Add the Type C bus for plug alternate modes which are being
> > > registered via the Type C connector class. This ensures that udev events
> > > get generated when plug alternate modes are registered (and not just for
> > > partner/port alternate modes), even though the Type C bus doesn't link
> > > plug alternate mode devices to alternate mode drivers.
> >
> > I still don't understand how is the uevent related to the bus? If you
> > check the device_add() function, on line 2917, kobject_uevent() is
> > called unconditionally. The device does not need a bus for that event
> > to be generated.
>
> My initial thought process was to see what is the difference in the adev device
> initialization between partner altmode and plug altmode (the only difference I saw in
> typec_register_altmode() was regarding the bus field).
>
> Yes, kobject_uevent() is called unconditionally, but it's return value isn't checked,
> so we don't know if it succeeded or not.
>
> In the case of cable plug altmode, I see it fail with the following error[1]:
>
> [ 114.431409] kobject: 'port1-plug0.0' (000000004ad42956): kobject_uevent_env: filter function caused the event to drop!
>
> I think the filter function which is called is this one: drivers/base/core.c: dev_uevent_filter() [2]
>
> static int dev_uevent_filter(struct kset *kset, struct kobject *kobj)
> {
> struct kobj_type *ktype = get_ktype(kobj);
>
> if (ktype == &device_ktype) {
> struct device *dev = kobj_to_dev(kobj);
> if (dev->bus)
> return 1;
> if (dev->class)
> return 1;
> }
> return 0;
> }
>
> So, both the "if (dev->bus)" and "if (dev->class)" checks are failing here. In the case of partner alt modes, bus is set by the class.c code
> so this check likely returns 1 in that case.
OK. I understand the issue now. So I would say that the proper
solution to this problem is to link the alt modes with the class
instead of the bus. That is much smaller change IMO.
thanks,
--
heikki
