linux-kernel - Re: [PATCHv6 1/3] usb: USB Type-C connector class

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Message-ID: <20160830114950.GB1751@kuha.fi.intel.com>
Date:   Tue, 30 Aug 2016 14:49:50 +0300
From:   Heikki Krogerus <heikki.krogerus@...ux.intel.com>
To:     Oliver Neukum <oneukum@...e.com>
Cc:     Guenter Roeck <linux@...ck-us.net>,
        Vincent Palatin <vpalatin@...omium.org>,
        Bin Gao <bin.gao@...ux.intel.com>,
        Felipe Balbi <felipe.balbi@...ux.intel.com>,
        Greg KH <gregkh@...uxfoundation.org>,
        linux-kernel@...r.kernel.org, linux-usb@...r.kernel.org
Subject: Re: [PATCHv6 1/3] usb: USB Type-C connector class

On Tue, Aug 30, 2016 at 01:16:46PM +0200, Oliver Neukum wrote:
> On Tue, 2016-08-30 at 13:04 +0300, Heikki Krogerus wrote:
> > On Tue, Aug 30, 2016 at 11:32:01AM +0200, Oliver Neukum wrote:
> 
> Hi,
> 
> > > On Mon, 2016-08-29 at 15:36 +0300, Heikki Krogerus wrote:
> > > > +What:          /sys/class/typec/<port>/current_data_role
> > > > +Date:          June 2016
> > > > +Contact:       Heikki Krogerus <heikki.krogerus@...ux.intel.com>
> > > > +Description:
> > > > +               The current USB data role the port is operating in.
> > > > This
> > > > +               attribute can be used for requesting data role
> > > > swapping on the
> > > > +               port. Swapping is only supported as an asynchronous
> > > > operation
> > > > +               and requires polling of the attribute in order to know
> > > > the
> > > > +               result, so successful write operation does not mean
> > > > successful
> > > > +               swap.
> > > > +
> > > 
> > > That is badly formulated. Does it mean that poll() or select()
> > > can be used or does the value need to be repearedly read?
> > 
> > Does polling not always mean poll/select?
> 
> No, it does not.
> 
> > > And how would you learn about an error?
> > 
> > This is what I'm also really worried about. I'm now wondering did I
> > give up too easily on this to Guenter in hope to move this thing
> > forward. He said it's problematic to do these calls synchronously for
> 
> Error reporting does not require a synchronous operation. Reporting
> it in the next read() or write() and making it pollable is perfectly
> viable. It just must not be silently dropped.

OK, I think I got it. I need to document that. I'll also add
get_pr/dr/vconn hooks to the API for getting the status.


Thanks Oliver,

-- 
heikki