linux-kernel - Re: [PATCH v2 14/28] thunderbolt: Extend tunnel creation to more than 2 adjacent switches

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Message-ID: <20190212125417.4an7efllnf7pqw2v@wunner.de>
Date:   Tue, 12 Feb 2019 13:54:17 +0100
From:   Lukas Wunner <lukas@...ner.de>
To:     Mika Westerberg <mika.westerberg@...ux.intel.com>
Cc:     linux-kernel@...r.kernel.org,
        Michael Jamet <michael.jamet@...el.com>,
        Yehezkel Bernat <YehezkelShB@...il.com>,
        Andreas Noever <andreas.noever@...il.com>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Subject: Re: [PATCH v2 14/28] thunderbolt: Extend tunnel creation to more
 than 2 adjacent switches

On Mon, Feb 11, 2019 at 10:45:58AM +0200, Mika Westerberg wrote:
> On Sun, Feb 10, 2019 at 04:33:28PM +0100, Lukas Wunner wrote:
> > at the bottom of this page there's
> > a figure showing a PCI tunnel between non-adjacent switches (blue line):
> > 
> > https://developer.apple.com/library/archive/documentation/HardwareDrivers/Conceptual/ThunderboltDevGuide/Basics/Basics.html
> > 
> Are you sure Apple actually uses setup like that? I think I have never
> seen such configuration happening on any of the devices I have.

Sorry, I don't know if they actually use that.


> I can update the changelog to mention that if you think it is useful.
> Something like below maybe?
> 
>  PCIe actually does not need this as it is typically a daisy chain
>  between two adjacent switches but this way we do not need to hard-code
>  creation of the tunnel.

LGTM, thanks.


> > > +	i = 0;
> > > +	tb_for_each_port(in_port, src, dst)
> > > +		i++;
> > 
> > This looks more complicated than necessary.  Isn't the path length
> > always the length of the route string from in_port switch to out_port
> > switch, plus 2 for the adapter on each end?  Or do paths without
> > adapters exist?
> 
> Yes, I think you are right.

Simply subtracting the depths of the start and end port's switch also yields
the path length.  Of course this assumes that tunnels aren't established
between non-adjacent switches, but your algorithm doesn't do that.

Thanks,

Lukas