linux-kernel - Re: [PATCH] usb: typec: Add a sysfs node to manage port type

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Date:   Tue, 23 May 2017 16:39:01 +0300
From:   Heikki Krogerus <heikki.krogerus@...ux.intel.com>
To:     Guenter Roeck <linux@...ck-us.net>
Cc:     Badhri Jagan Sridharan <badhri@...gle.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org,
        Oliver Neukum <oneukum@...e.com>
Subject: Re: [PATCH] usb: typec: Add a sysfs node to manage port type

On Tue, May 23, 2017 at 06:16:28AM -0700, Guenter Roeck wrote:
> On 05/23/2017 03:46 AM, Heikki Krogerus wrote:
> > Hi,
> > 
> > On Mon, May 22, 2017 at 01:05:42PM -0700, Badhri Jagan Sridharan wrote:
> > > User space applications in some cases have the need to enforce a
> > > specific port type(DFP/UFP/DRP). This change allows userspace to
> > > attempt setting the desired port type. Low level drivers can
> > > however reject the request if the specific port type is not supported.
> > > 
> > > Signed-off-by: Badhri Jagan Sridharan <Badhri@...gle.com>
> > > ---
> > >   Documentation/ABI/testing/sysfs-class-typec | 13 ++++++++++
> > >   drivers/usb/typec/typec.c                   | 40 +++++++++++++++++++++++++++++
> > >   include/linux/usb/typec.h                   |  4 +++
> > >   3 files changed, 57 insertions(+)
> > > 
> > > diff --git a/Documentation/ABI/testing/sysfs-class-typec b/Documentation/ABI/testing/sysfs-class-typec
> > > index d4a3d23eb09c..853b2ef73641 100644
> > > --- a/Documentation/ABI/testing/sysfs-class-typec
> > > +++ b/Documentation/ABI/testing/sysfs-class-typec
> > > @@ -73,6 +73,19 @@ Description:
> > >   		Valid values: source, sink, none (to remove preference)
> > > +What:           /sys/class/typec/<port>/port_type
> > > +Date:           May 2017
> > > +Description:
> > > +		Indicates the type of the port. This attribute can be used for
> > > +		requesting a change in the port type. Port type change is
> > > +		supported as a synchronous operation, so write(2) to the
> > > +		attribute will not return until the operation has finished.
> > > +
> > > +		Valid values:
> > > +		- DRP
> > > +		- DFP
> > > +		- UFP
> > > 
> > >   What:		/sys/class/typec/<port>/supported_accessory_modes
> > >   Date:		April 2017
> > >   Contact:	Heikki Krogerus <heikki.krogerus@...ux.intel.com>
> > > diff --git a/drivers/usb/typec/typec.c b/drivers/usb/typec/typec.c
> > > index 89e540bb7ff3..684a13bb744d 100644
> > > --- a/drivers/usb/typec/typec.c
> > > +++ b/drivers/usb/typec/typec.c
> > > @@ -789,6 +789,12 @@ static const char * const typec_data_roles[] = {
> > >   	[TYPEC_HOST]	= "host",
> > >   };
> > > +static const char * const typec_port_types[] = {
> > > +	[TYPEC_PORT_DFP] = "dfp",
> > > +	[TYPEC_PORT_UFP] = "ufp",
> > > +	[TYPEC_PORT_DRP] = "drp",
> > > +};
> > 
> > The meaning of those abbreviations has changed in every version of the
> > spec since v1.0 which makes me a bit uncomfortable using them with the
> > attributes. In USB Type-C specification v1.2, DRP now means
> > Dual-Role-Power, but DFP and UFP are used with USB data operation.
> > 
> > I would prefer "source, "sink" and "drp". Actually, I don't even like
> > "drp". How about "dual" instead?
> > 
> > >   static ssize_t
> > >   preferred_role_store(struct device *dev, struct device_attribute *attr,
> > >   		     const char *buf, size_t size)
> > > @@ -926,6 +932,39 @@ static ssize_t power_role_show(struct device *dev,
> > >   }
> > >   static DEVICE_ATTR_RW(power_role);
> > > +static ssize_t
> > > +port_type_store(struct device *dev, struct device_attribute *attr,
> > > +			const char *buf, size_t size)
> > > +{
> > > +	struct typec_port *port = to_typec_port(dev);
> > > +	int ret;
> > > +
> > > +	if (!port->cap->port_type_set) {
> > > +		dev_dbg(dev, "changing port type not supported\n");
> > > +		return -EOPNOTSUPP;
> > > +	}
> > > +
> > > +	ret = sysfs_match_string(typec_port_types, buf);
> > > +	if (ret < 0)
> > > +		return ret;
> > > +
> > > +	ret = port->cap->port_type_set(port->cap, ret);
> > > +	if (ret)
> > > +		return ret;
> > > +
> > > +	return size;
> > > +}
> > > +
> > > +static ssize_t
> > > +port_type_show(struct device *dev, struct device_attribute *attr,
> > > +		char *buf)
> > > +{
> > > +	struct typec_port *port = to_typec_port(dev);
> > > +
> > > +	return sprintf(buf, "%s\n", typec_port_types[port->cap->type]);
> > > +}
> > > +static DEVICE_ATTR_RW(port_type);
> > 
> > This doesn't tell the user the capabilities of the port. All the
> > supported roles should be listed here like with the other attributes,
> > the active one in brackets. This probable means we need a small
> > addition/change to the API too.

Sorry, not the API..

> typec_capability already lists the port type. Presumably it can be
> restricted to TYPEC_PORT_DFP or TYPEC_PORT_UFP only if it is reported
> as TYPEC_PORT_DRP. Am I missing something ?

I mean, we should not overwrite the type member in typec_capability.
DRP capable port is still DRP capable even if we fix it to DFP or UFP.
So the active, fixed role, should be stored to struct typec_port.


Thanks,

-- 
heikki