linux-kernel - Re: [PATCH 4/5] thunderbolt: Correlate PCI devices with Thunderbolt ports

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Message-ID: <20180910094454.GJ14465@lahna.fi.intel.com>
Date:   Mon, 10 Sep 2018 12:44:54 +0300
From:   Mika Westerberg <mika.westerberg@...ux.intel.com>
To:     Lukas Wunner <lukas@...ner.de>
Cc:     Andreas Noever <andreas.noever@...il.com>,
        Michael Jamet <michael.jamet@...el.com>,
        Yehezkel Bernat <YehezkelShB@...il.com>,
        Stephen Hemminger <stephen@...workplumber.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 4/5] thunderbolt: Correlate PCI devices with Thunderbolt
 ports

Hi Lukas,

On Sun, Sep 09, 2018 at 11:42:01PM +0200, Lukas Wunner wrote:
> Ideas what we can do with correlation:
> 
> * Represent the relationship between PCI devices and Thunderbolt ports
>   with symlinks in sysfs.

I wonder is that really useful? I don't think we should be adding sysfs
entries without any real reason why it would be needed and who would be
using them.

> * Thunderbolt controllers up to revision 1 of Cactus Ridge 4C have to
>   use INTx because MSI signaling is broken.  This results in hotplug
>   ports sharing interrupts with other devices and, when daisy-chaining
>   multiple affected Thunderbolt controllers, can lead to extremely
>   unbalanced interrupt usage.  To avoid this we could prefer downstream
>   ports for tunnel establishment which do not share interrupts (based
>   on the nr_actions field of the correlated PCI device's irq_desc).
> 
> * Alternatively, we could use non-working MSI signaling on affected
>   controllers and synthesize an interrupt whenever a tunnel is
>   established or goes down on unplug.

Problem I see with this patch as it stands is that you add 200+ lines of
code into the driver that is not being used by anything as far as I
understand it.