linux-kernel - Re: [PATCH 18/24] thunderbolt: Store Thunderbolt generation in the switch structure

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Date:   Sun, 21 May 2017 13:47:14 +0300
From:   Mika Westerberg <mika.westerberg@...ux.intel.com>
To:     "Bernat, Yehezkel" <yehezkel.bernat@...el.com>
Cc:     "Levy, Amir (Jer)" <amir.jer.levy@...el.com>,
        Lukas Wunner <lukas@...ner.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Andreas Noever <andreas.noever@...il.com>,
        "Jamet, Michael" <michael.jamet@...el.com>,
        Andy Lutomirski <luto@...nel.org>,
        "Mario.Limonciello@...l.com" <Mario.Limonciello@...l.com>,
        "Jared.Dominguez@...l.com" <Jared.Dominguez@...l.com>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 18/24] thunderbolt: Store Thunderbolt generation in the
 switch structure

On Sun, May 21, 2017 at 09:55:55AM +0000, Bernat, Yehezkel wrote:
> 
> 
> > -----Original Message-----
> > From: Levy, Amir (Jer)
> > Sent: Sunday, May 21, 2017 11:07
> > To: Mika Westerberg <mika.westerberg@...ux.intel.com>; Lukas Wunner
> > <lukas@...ner.de>
> > Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>; Andreas Noever
> > <andreas.noever@...il.com>; Jamet, Michael <michael.jamet@...el.com>;
> > Bernat, Yehezkel <yehezkel.bernat@...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 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.

Fair enough :) Then we just need to remember to update the function here
as new generations get added and tested.

I suppose you don't know either if we could use the revision or similar
field in the switch config space to determine generation somehow?