Re: [PATHCv10 1/2] usb: USB Type-C connector class

[Guenter Roeck]

On 11/14/2016 11:07 PM, Greg KH wrote:
> On Mon, Nov 14, 2016 at 12:46:50PM -0800, Guenter Roeck wrote:
> > On Mon, Nov 14, 2016 at 02:32:35PM +0200, Heikki Krogerus wrote:
> > > Hi Greg,
> > >
> > > On Mon, Nov 14, 2016 at 10:51:48AM +0100, Greg KH wrote:
> > > > On Mon, Sep 19, 2016 at 02:16:56PM +0300, Heikki Krogerus wrote:
> > > > > The purpose of USB Type-C connector class is to provide
> > > > > unified interface for the user space to get the status and
> > > > > basic information about USB Type-C connectors on a system,
> > > > > control over data role swapping, and when the port supports
> > > > > USB Power Delivery, also control over power role swapping
> > > > > and Alternate Modes.
> > > > >
> > > > > Reviewed-by: Guenter Roeck <linux@xxxxxxxxxxxx>
> > > > > Tested-by: Guenter Roeck <linux@xxxxxxxxxxxx>
> > > > > Signed-off-by: Heikki Krogerus <heikki.krogerus@xxxxxxxxxxxxxxx>
> > > > > ---
> > > > >  Documentation/ABI/testing/sysfs-class-typec |  218 ++++++
> > > > >  Documentation/usb/typec.txt                 |  103 +++
> > > > >  MAINTAINERS                                 |    9 +
> > > > >  drivers/usb/Kconfig                         |    2 +
> > > > >  drivers/usb/Makefile                        |    2 +
> > > > >  drivers/usb/typec/Kconfig                   |    7 +
> > > > >  drivers/usb/typec/Makefile                  |    1 +
> > > > >  drivers/usb/typec/typec.c                   | 1075 +++++++++++++++++++++++++++
> > > > >  include/linux/usb/typec.h                   |  252 +++++++
> > > > >  9 files changed, 1669 insertions(+)
> > > > >  create mode 100644 Documentation/ABI/testing/sysfs-class-typec
> > > > >  create mode 100644 Documentation/usb/typec.txt
> > > > >  create mode 100644 drivers/usb/typec/Kconfig
> > > > >  create mode 100644 drivers/usb/typec/Makefile
> > > > >  create mode 100644 drivers/usb/typec/typec.c
> > > > >  create mode 100644 include/linux/usb/typec.h
> > [ ... ]
> >
> > > > > +
> > > > > +int typec_connect(struct typec_port *port, struct typec_connection *con)
> > > > > +{
> > > > > +	int ret;
> > > > > +
> > > > > +	if (!con->partner && !con->cable)
> > > > > +		return -EINVAL;
> > > > > +
> > > > > +	port->connected = 1;
> > > > > +	port->data_role = con->data_role;
> > > > > +	port->pwr_role = con->pwr_role;
> > > > > +	port->vconn_role = con->vconn_role;
> > > > > +	port->pwr_opmode = con->pwr_opmode;
> > > > > +
> > > > > +	kobject_uevent(&port->dev.kobj, KOBJ_CHANGE);
> > > >
> > > > This worries me.  Who is listening for it?  What will you do with it?
> > > > Shouldn't you just poll on an attribute file instead?
> > >
> > > Oliver! Did you need this or can we remove it?
> > >
> > > I remember I removed the "connected" attribute because you did not see
> > > any use for it at one point. I don't remember the reason exactly why?
> >
> > The Android team tells me that they are currently using the udev events
> > to track port role changes, and to detect presence of port partner.
> >
> > Also, there are plans to track changes on usbc*cable to differentiate
> > between cable attach vs. device being attached on the remote end.
> >
> > What is the problem with using kobject_uevent() and thus presumably
> > udev events ?
>
> It's not a "normal" thing to do and is pretty "heavy" to do.  What does
> userspace do with that change event?  Does it read specific attributes?
> What causes the event to happen in the kernel, is it really just a
> change in the specific object, or do new ones get added/removed?
>
> In short, document the heck out of this please so people know how to use
> it, and what is happening when the event happens.

Badhri,

can you clarify which events you are using in detail, and what for ?

Thanks,
Guenter