linux-kernel - Re: [PATCH v3 19/27] thunderbolt: Add new Thunderbolt PCI IDs

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Date:   Mon, 5 Jun 2017 16:52:34 +0300
From:   Mika Westerberg <mika.westerberg@...ux.intel.com>
To:     Lukas Wunner <lukas@...ner.de>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Andreas Noever <andreas.noever@...il.com>,
        Michael Jamet <michael.jamet@...el.com>,
        Yehezkel Bernat <yehezkel.bernat@...el.com>,
        Amir Levy <amir.jer.levy@...el.com>,
        Andy Lutomirski <luto@...nel.org>, Mario.Limonciello@...l.com,
        Jared.Dominguez@...l.com,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 19/27] thunderbolt: Add new Thunderbolt PCI IDs

On Mon, Jun 05, 2017 at 03:46:43PM +0200, Lukas Wunner wrote:
> On Mon, Jun 05, 2017 at 04:33:34PM +0300, Mika Westerberg wrote:
> > 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?
> 
> Yes, great, thanks!
> 
> And in "auto" mode, it's ICM on non-Macs and TBT3-Macs, and native for
> TBT1/TBT2-Macs, right?

Yes, that's correct.

> Some Falcon Ridge Macs support ICM as well (e.g. the MacBookPro11,4
> and MacBookPro11,5 introduced 2015), but maybe not all of them.
> This will have to be tested.  If all of them support it, we could
> later default to ICM for those as well, or use DMI data to constrain
> it to specific models.

Unfortunately starting ICM on Falcon Ridge Macs does not work (I tried
that already) so there we need to stick with the native implementation.