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Date: Mon, 5 Jun 2017 16:33:34 +0300
From: Mika Westerberg <mika.westerberg@linux.intel.com>
To: Lukas Wunner <lukas@wunner.de>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Andreas Noever <andreas.noever@gmail.com>,
        Michael Jamet <michael.jamet@intel.com>,
        Yehezkel Bernat <yehezkel.bernat@intel.com>,
        Amir Levy <amir.jer.levy@intel.com>, Andy Lutomirski <luto@kernel.org>,
        Mario.Limonciello@dell.com, Jared.Dominguez@dell.com,
        Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH v3 19/27] thunderbolt: Add new Thunderbolt PCI IDs
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On Mon, Jun 05, 2017 at 03:55:07PM +0300, Mika Westerberg wrote:
> > Yes, it's useful to have ICM-based Thunderbolt on Macs and personally
> > I'm totally fine with making it the default for Macs which support it.
> > (I can't speak for Andreas, obviously.)
> > 
> > However it would be great to give people the *choice* between ICM versus
> > native mode, for at least two reasons:
> > 
> > (1) Native mode uses free software.  (I assume the ICM firmware remains
> >     closed source.)
> > 
> > (2) Native mode allows more versatility, e.g. how PCI tunnels are set up
> >     to chained devices: PCI fanout or PCI direct routing, see:
> >     https://developer.apple.com/library/content/documentation/HardwareDrivers/Conceptual/ThunderboltDevGuide/Basics/Basics.html
> > 
> >     Apple supports traffic prioritization to enable audio over Thunderbolt
> >     with higher accuracy / minimal skew, I assume their choice to use
> >     native mode was largely motivated by being able to support specialized
> >     applications like that which are difficult or perhaps impossible to
> >     implement in firmware:
> >     http://pdfpiw.uspto.gov/.piw?Docid=09015384
> 
> Right, but do we need to do it now before we have got any feedback from
> users using Macs with Alpine Ridge and ICM? We can always add the module
> parameter later if really needed.

It turns out that this is not too big change after all so I think it can
be included in the ICM patch if you want.

Basically we would have module parameter:

	cm=auto|native|icm

where auto is the default.

Does that work?