linux-kernel - Re: [PATCH V2] usb: typec: Add sysfs node to show connector orientation

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Date:   Wed, 23 Oct 2019 08:01:26 -0700
From:   Guenter Roeck <linux@...ck-us.net>
To:     Heikki Krogerus <heikki.krogerus@...ux.intel.com>
Cc:     Puma Hsu <pumahsu@...gle.com>, gregkh@...uxfoundation.org,
        badhri@...gle.com, kyletso@...gle.com, albertccwang@...gle.com,
        rickyniu@...gle.com, linux-usb@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH V2] usb: typec: Add sysfs node to show connector
 orientation

On Wed, Oct 23, 2019 at 05:29:00PM +0300, Heikki Krogerus wrote:
> On Wed, Oct 23, 2019 at 06:44:39AM -0700, Guenter Roeck wrote:
> > On 10/23/19 1:32 AM, Heikki Krogerus wrote:
> > > +Guenter
> > > 
> > > On Tue, Oct 22, 2019 at 04:59:24PM +0800, Puma Hsu wrote:
> > > > Export the Type-C connector orientation so that user space
> > > > can get this information.
> > > > 
> > > > Signed-off-by: Puma Hsu <pumahsu@...gle.com>
> > > > ---
> > > >   Documentation/ABI/testing/sysfs-class-typec | 11 +++++++++++
> > > >   drivers/usb/typec/class.c                   | 18 ++++++++++++++++++
> > > >   2 files changed, 29 insertions(+)
> > > > 
> > > > diff --git a/Documentation/ABI/testing/sysfs-class-typec b/Documentation/ABI/testing/sysfs-class-typec
> > > > index d7647b258c3c..b22f71801671 100644
> > > > --- a/Documentation/ABI/testing/sysfs-class-typec
> > > > +++ b/Documentation/ABI/testing/sysfs-class-typec
> > > > @@ -108,6 +108,17 @@ Contact:	Heikki Krogerus <heikki.krogerus@...ux.intel.com>
> > > >   Description:
> > > >   		Revision number of the supported USB Type-C specification.
> > > > +What:		/sys/class/typec/<port>/connector_orientation
> > > > +Date:		October 2019
> > > > +Contact:	Puma Hsu <pumahsu@...gle.com>
> > > > +Description:
> > > > +		Indicates which typec connector orientation is configured now.
> > > > +		cc1 is defined as "normal" and cc2 is defined as "reversed".
> > > > +
> > > > +		Valid value:
> > > > +		- unknown (nothing configured)
> > > 
> > > "unknown" means we do not know the orientation.
> > > 
> > > > +		- normal (configured in cc1 side)
> > > > +		- reversed (configured in cc2 side)
> > > 
> > > Guenter, do you think "connector_orientation" OK. I proposed it, but
> > > I'm now wondering if something like "polarity" would be better?
> > > 
> > 
> > Yes, or just "orientation". I don't see the value in the "connector_" prefix.
> > I also wonder if "unknown" is really correct. Is it really unknown, or
> > does it mean that the port is disconnected ?
> 
> Unknown means we don't know the orientation. We don't always have that
> information available to us. With UCSI we simply do not know it.
> 
> I think this file needs to be hidden after all if we don't know the
> cable plug orientation.
> 
Making the attribute appear and disappear may cause difficulties for
userspace.

> How about empty string instead of "unknown"?
> 
An empty string might also be challenging for userspace.

"unknown" is fine if it is really unknown. With that in mind,
I wonder what value that attribute has for userspace, but presumably
there must be some use case. I assume it is purely informational.

In summary, I would suggest to name the attribute either "orientation"
or "polarity".

Thanks,
Guenter