linux-kernel - Re: [RFC PATCHv2] usb: USB Type-C Connector Class

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Message-ID: <20160523165212.GA5964@roeck-us.net>
Date:	Mon, 23 May 2016 09:52:12 -0700
From:	Guenter Roeck <linux@...ck-us.net>
To:	Oliver Neukum <oneukum@...e.com>
Cc:	Andy Shevchenko <andy.shevchenko@...il.com>,
	Rajaram R <rajaram.officemail@...il.com>,
	Felipe Balbi <felipe.balbi@...ux.intel.com>,
	Heikki Krogerus <heikki.krogerus@...ux.intel.com>,
	Mathias Nyman <mathias.nyman@...ux.intel.com>,
	Greg KH <gregkh@...uxfoundation.org>,
	linux-kernel@...r.kernel.org, linux-usb@...r.kernel.org
Subject: Re: [RFC PATCHv2] usb: USB Type-C Connector Class

On Mon, May 23, 2016 at 05:55:04PM +0200, Oliver Neukum wrote:
> On Mon, 2016-05-23 at 07:43 -0700, Guenter Roeck wrote:
> > On 05/23/2016 06:58 AM, Oliver Neukum wrote:
> 
> > > Now I am confused. Are you saying that the choice of Alternate Mode does
> > > not belong into user space?
> > >
> > 
> > No; sorry for the confusion. The above was meant to apply to my use
> > of "preferred mode", not yours. I was trying to say that the choice of
> > preferred roles (which determines if Try.SRC or Try.SNK is enabled)
> > should belong primarily into the kernel, to be determined by the platform
> > (presumably via ACPI, devicetree data, or platform data). If it should
> 
> Why on earth? That is most clearly a policy decision.
> 

The question is not that much if it is policy (it is), but if the policy
should be driven by the platform or by user space. I think there needs
to be at least a default driven by the platform. As already mentioned,
I am ok with a means to override this platform default from user space.
But if user space doesn't say, there still needs to be a default.

Thanks,
Guenter

> > be possible to override it by user space is a different question. That
> > might be useful, at least for testing. If so, does such an override
> > belong into the class or into the PD driver ? Good question. I am fine
> > either way.
> 
> Well, if platform data has a default, I suppose we ought to use it.
> 
> > I don't really have a strong opinion about alternate mode selection. I would
> > think that there should be a kernel (platform) default, possibly determined
> > by the alternate mode itself, but I also think that it should be selectable
> > by user space. Question is if that should be done through the alternate mode
> > driver or through the class (example: alternate modes used for firmware
> 
> I would say that the ought to be a driver for type C which controls
> alternate modes and roles.
> 
> 	Regards
> 		Oliver
> 
>