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From: Andy Shevchenko <andy.shevchenko@gmail.com>
Date: Sat, 27 May 2017 18:45:24 +0300
Message-ID: <CAHp75VdacYoO2wpojPS1CDeJr-V=0U8JH=dx6p9soBswZ+D8JQ@mail.gmail.com>
Subject: Re: [PATCH v2 09/27] thunderbolt: Convert switch to a device
To: Mika Westerberg <mika.westerberg@linux.intel.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Andreas Noever <andreas.noever@gmail.com>,
        Michael Jamet <michael.jamet@intel.com>,
        Yehezkel Bernat <yehezkel.bernat@intel.com>,
        Lukas Wunner <lukas@wunner.de>, Amir Levy <amir.jer.levy@intel.com>,
        Andy Lutomirski <luto@kernel.org>,
        Mario Limonciello <Mario.Limonciello@dell.com>,
        Jared.Dominguez@dell.com,
        Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
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On Fri, May 26, 2017 at 7:09 PM, Mika Westerberg
<mika.westerberg@linux.intel.com> wrote:
> Thunderbolt domain consists of switches that are connected to each
> other, forming a bus. This will convert each switch into a real Linux
> device structure and adds them to the domain. The advantage here is
> that we get all the goodies from the driver core, like reference
> counting and sysfs hierarchy for free.
>
> Also expose device identification information to the userspace via new
> sysfs attributes.
>
> In order to support internal connection manager (ICM) we separate switch
> configuration into its own function (tb_switch_configure()) which is
> only called by the existing native connection manager implementation
> used on Macs.

> +       /*
> +        * The newer controllers include fused UUID as part of link
> +        * controller specific registers
> +        */
> +       cap = tb_switch_find_vsec_cap(sw, TB_VSEC_CAP_LINK_CONTROLLER);
> +       if (cap > 0) {
> +               tb_sw_read(sw, uuid, TB_CFG_SWITCH, cap + 3, 4);
> +       } else {
> +               /*
> +                * By default the UUID will be based on UID where upper two
> +                * dwords are filled with ones.
> +                */
> +               uuid[0] = sw->uid & 0xffffffff;
> +               uuid[1] = (sw->uid >> 32) & 0xffffffff;
> +               uuid[2] = 0xffffffff;
> +               uuid[3] = 0xffffffff;
> +       }

It might make sense to add some comment as we discussed earlier
(privately) about (non-)compatibiliness with UUID by spec and why 0xff
are used.

-- 
With Best Regards,
Andy Shevchenko