linux-kernel - Re: [PATCH 02/24] thunderbolt: Do not try to read UID if DROM offset is read as 0

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Message-ID: <CAMxnaaWubkud4kWpVpoxGDjLdSKNTKk7R-MyDnZisrmHGHzZuQ@mail.gmail.com>
Date:   Mon, 22 May 2017 22:57:35 +0200
From:   Andreas Noever <andreas.noever@...il.com>
To:     Mika Westerberg <mika.westerberg@...ux.intel.com>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Michael Jamet <michael.jamet@...el.com>,
        Yehezkel Bernat <yehezkel.bernat@...el.com>,
        Lukas Wunner <lukas@...ner.de>,
        Amir Levy <amir.jer.levy@...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" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 02/24] thunderbolt: Do not try to read UID if DROM offset
 is read as 0

On Mon, May 22, 2017 at 10:38 PM, Mika Westerberg
<mika.westerberg@...ux.intel.com> wrote:
> On Mon, May 22, 2017 at 08:41:22PM +0200, Andreas Noever wrote:
>> Yes there is a check for the root switch, but also one that checks the
>> return code of tb_drom_read_uid_only :)
>>
>> err = tb_drom_read_uid_only(sw, &uid);
>> if (err) {
>>     tb_sw_warn(sw, "uid read failed\n");
>>     return err;
>> }
>> if (sw != sw->tb->root_switch && sw->uid != uid) {
>>
>>
>> The reason it works on the Mac is because drom_offset is not 0, so the
>> new branch in tb_drom_read_uid_only is not taken. Probably this is the
>> case for all Cactus Ridge models and Alpine Ridge doesn't go there
>> since it uses the ICM?
>
> Yes in case of ICM we don't call the function at all.
>
>> Still it wouldn't hurt to only read the uid if
>> sw != root_switch, the value is not used if sw == root_switch.
>
> I agree. I'll update the code so that it will only read and check UID
> when we are not dealing with the root switch.
Thanks,
Andreas