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

[Greg Kroah-Hartman]

On Tue, Oct 01, 2019 at 06:07:34PM +0300, Mika Westerberg wrote:
> On Tue, Oct 01, 2019 at 04:53:54PM +0200, Greg Kroah-Hartman wrote:
> > 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?
> 
> OK, but does that break existing .configs? I mean if you have already
> CONFIG_THUNDERBOLT in your .config/defconfig does it now just get
> dropped silently?

Yup.  And then you get asked about CONFIG_USB4

> For example firewire has CONFIG_FIREWIRE even though the "standard" name
> is IEEE 1394. I was thinking maybe we can do the same for
> USB4/Thunderbolt?

It comes down to the what do you want to do for the next 20+ years,
explain to people that "to get USB4 support, enable CONFIG_THUNDERBOLT"?

:)

thanks,

greg k-h