linux-kernel - Re: [RFC PATCH 17/22] thunderbolt: Add initial support for USB4

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Date:   Tue, 1 Oct 2019 17:22:13 +0200
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Mario.Limonciello@...l.com
Cc:     mika.westerberg@...ux.intel.com, linux-usb@...r.kernel.org,
        andreas.noever@...il.com, michael.jamet@...el.com,
        YehezkelShB@...il.com, rajmohan.mani@...el.com,
        nicholas.johnson-opensource@...look.com.au, lukas@...ner.de,
        stern@...land.harvard.edu, anthony.wong@...onical.com,
        linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH 17/22] thunderbolt: Add initial support for USB4

On Tue, Oct 01, 2019 at 02:59:06PM +0000, Mario.Limonciello@...l.com wrote:
> 
> 
> > -----Original Message-----
> > From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> > Sent: Tuesday, October 1, 2019 9:54 AM
> > To: Mika Westerberg
> > Cc: linux-usb@...r.kernel.org; Andreas Noever; Michael Jamet; Yehezkel Bernat;
> > Rajmohan Mani; Nicholas Johnson; Lukas Wunner; Alan Stern; Limonciello, Mario;
> > Anthony Wong; linux-kernel@...r.kernel.org
> > Subject: Re: [RFC PATCH 17/22] thunderbolt: Add initial support for USB4
> > 
> > 
> > [EXTERNAL EMAIL]
> > 
> > On Tue, Oct 01, 2019 at 04:09:05PM +0300, Mika Westerberg wrote:
> > > On Tue, Oct 01, 2019 at 02:47:48PM +0200, Greg Kroah-Hartman wrote:
> > > > > -	  Thunderbolt Controller driver. This driver is required if you
> > > > > -	  want to hotplug Thunderbolt devices on Apple hardware or on PCs
> > > > > -	  with Intel Falcon Ridge or newer.
> > > > > +	  USB4 (Thunderbolt) driver. USB4 is the public spec based on
> > > > > +	  Thunderbolt 3 protocol. This driver is required if you want to
> > > > > +	  hotplug Thunderbolt and USB4 compliant devices on Apple
> > > > > +	  hardware or on PCs with Intel Falcon Ridge or newer.
> > > >
> > > > Wait, did "old" thunderbolt just get re-branded as USB4?
> > >
> > > Not but the driver started supporting USB4 as well :)
> > >
> > > USB4 is pretty much public spec of Thunderbolt 3 but with some
> > > differences in register layouts (this is because Thunderbolt uses some
> > > vendor specific capabilities which are now moved to more "standard"
> > > places).
> > 
> > Ok, then we need to rename the Kconfig option as well, otherwise no one
> > will "know" that this changed, so they will not be prompted for it.
> > 
> > > > Because if I have an "old" laptop that needs Thunderbolt support, how am
> > > > I going to know it is now called USB4 instead?
> > >
> > > Well the Kconfig option tries to have both names there:
> > >
> > >   tristate "USB4 (Thunderbolt) support"
> > >
> > > and then
> > >
> > >   USB4 (Thunderbolt) driver. USB4 is the public spec based on
> > >   Thunderbolt 3 protocol. This driver is required if you want to hotplug
> > >   Thunderbolt and USB4 compliant devices on Apple hardware or on PCs
> > >   with Intel Falcon Ridge or newer.
> > >
> > > and the Kconfig option is still CONFIG_THUNDERBOLT. I know this is
> > > confusing but I don't have better ideas how we can advertise both. I
> > > borrowed this "format" from firewire.
> > 
> > CONFIG_USB4 instead?
> 
> How about CONFIG_USB4_PCIE?
> 
> I think that will help align that certain aspects of USB4 can be built optionally.

What aspects?  We don't have that here at all.

I guess the parts of USB4 that are not just this "hook up the PCIe
lane" that need to still be developed?

thanks,
greg k-h