RE: [PATCH 18/24] thunderbolt: Store Thunderbolt generation in the switch structure

["Bernat, Yehezkel" <yehezkel.bernat@intel.com>]

> -----Original Message-----
> From: Levy, Amir (Jer)
> Sent: Sunday, May 21, 2017 11:07
> To: Mika Westerberg <mika.westerberg@linux.intel.com>; Lukas Wunner
> <lukas@wunner.de>
> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>; Andreas Noever
> <andreas.noever@gmail.com>; Jamet, Michael <michael.jamet@intel.com>;
> Bernat, Yehezkel <yehezkel.bernat@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 18/24] thunderbolt: Store Thunderbolt generation in the
> switch structure
> 
> On Sun, May 21 2017, 11:00 AM, Mika Westerberg wrote:
> > On Sun, May 21, 2017 at 10:40:41AM +0300, Mika Westerberg wrote:
> > > On Sun, May 21, 2017 at 07:35:21AM +0200, Lukas Wunner wrote:
> > > > On Sun, May 21, 2017 at 05:29:47AM +0000, Levy, Amir (Jer) wrote:
> > > > > On Sun, May 21 2017, 07:47 AM, Lukas Wunner wrote:
> > > > > > On Thu, May 18, 2017 at 05:39:08PM +0300, Mika Westerberg wrote:
> > > > > > > +
> > > > > > > +	default:
> > > > > > > +		sw->generation = 1;
> > > > > > > +		break;
> > > > > >
> > > > > > If someone adds an entry for, say, a new TB3 controller to
> > > > > > nhi_ids[] but forgets to update this function, the controller
> > > > > > is assigned the wrong generation number.  It might be better
> > > > > > to make TB3 the default and list each TB1 controller instead
> > > > > > since it's less likely for Intel to introduce an older gen chip.
> > > > > >
> > > > > > Generally I think it's problematic to require that multiple
> > > > > > files are touched whenever a new controller is added.  Isn't
> > > > > > the generation number or link speed (10/20/40) stored in some
> > > > > > register in PCI config space (VSEC 0x1234) or TB config space?
> > > > >
> > > > > How about setting information, that isn't available from PCI, in
> > > > > pci_device_id.driver_data when initializing nhi_ids[]?
> > > >
> > > > Right, that would also be possible, though reading the generation
> > > > number from a register would be more elegant, if such a register exists.
> > >
> > > I don't think there is such register but I can put this information
> > > to the driver_data instead.
> >
> > Actually these are Thunderbolt switch IDs, not NHI PCI IDs so I don't
> > think driver_data is the right place after all. So if no objections,
> > I'll update the function to default to TBT3 but keep the switch case
> > and add the TBT1 IDs + Win Ridge there.
> 
> There is correlation between switch ID to NHI ID.

I'm not sure defaulting to TBT3 is a good idea. ICM message format can be changed, DMA port can be different, nothing guaranties correct operation of the driver with newer unknown controllers.