linux-kernel - Re: [PATCH v3 19/36] thunderbolt: Extend tunnel creation to more than 2 adjacent switches

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Date:   Mon, 8 Apr 2019 11:49:04 +0200
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>,
        Christian Kellner <ckellner@...hat.com>,
        Mario.Limonciello@...l.com
Subject: Re: [PATCH v3 19/36] thunderbolt: Extend tunnel creation to more
 than 2 adjacent switches

On Mon, Apr 08, 2019 at 12:07:44PM +0300, Mika Westerberg wrote:
> On Mon, Apr 08, 2019 at 10:53:37AM +0200, Lukas Wunner wrote:
> > Hm, what other cases are there, i.e. what is the meaning of a tb_regs_hop's
> > "next_hop" field if "out_port" doesn't have a remote?  (And why does it
> > need to be tracked on the out_port?  In case a remote is added later?)
> 
> We also need to program HopIDs for adapter ports (PCIe, DP, NHI) in
> order to enable a path. The "next_hop" from NULL port to an adapter port
> tells the HopID a packet gets when it is routed to the adapter port and
> the adapter port registers then are used to specify which HopID means
> what (for PCIe there is only 8 but for DP there is 8 and 9, for NHI it
> can be anything the service driver has negotiated).

Okay, so in_hopids are the entries allocated in this port's hop config
space, whereas out_hopids only really bears significance for adapter
ports.  For null ports (in-between two adapter ports on a path),
out_hopids is identical to the in_hopids of the next hop (IIUC).

That probably merits mentioning in struct tb_port's kerneldoc.

Thanks,

Lukas