linux-kernel - Re: [RFC PATCH 00/22] thunderbolt: Add support for USB4

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Date:   Tue, 1 Oct 2019 14:49:54 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Mika Westerberg <mika.westerberg@...ux.intel.com>
Cc:     linux-usb@...r.kernel.org,
        Andreas Noever <andreas.noever@...il.com>,
        Michael Jamet <michael.jamet@...el.com>,
        Yehezkel Bernat <YehezkelShB@...il.com>,
        Rajmohan Mani <rajmohan.mani@...el.com>,
        Nicholas Johnson <nicholas.johnson-opensource@...look.com.au>,
        Lukas Wunner <lukas@...ner.de>,
        Alan Stern <stern@...land.harvard.edu>,
        Mario.Limonciello@...l.com,
        Anthony Wong <anthony.wong@...onical.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH 00/22] thunderbolt: Add support for USB4

On Tue, Oct 01, 2019 at 02:38:08PM +0300, Mika Westerberg wrote:
> Hi all,
> 
> I'm sending this as RFC because the series is still missing important
> features such as power management so not ready for merging. However, I
> think it is good to get any early feedback from the community. We are
> working to add support for the missing features.
> 
> USB4 is the public specification of Thunderbolt 3 protocol and can be
> downloaded here:
> 
>   https://www.usb.org/sites/default/files/USB4%20Specification_1.zip
> 
> USB4 is about tunneling different protocols over a single cable (in the
> same way as Thunderbolt). The current USB4 spec supports PCIe, Display Port
> and USB 3.x, and also software based protocols such as networking between
> domains (hosts).
> 
> So far PCs have been using firmware based Connection Manager and Apple
> systems have been using software based one. A Connection Manager is the
> entity that handles creation of different tunnel types through the USB4
> (and Thunderbolt) fabric. With USB4 the plan is to have software based
> Connection Manager everywhere but some early systems will also support
> firmware to allow OS downgrade for example.
> 
> Current Linux Thunderbolt driver supports both "modes" and can detect which
> one to use dynamically.
> 
> This series first adds support for Thunderbolt 3 devices to the software
> connection manager and then extends that to support USB4 compliant hosts
> and devices (this applies to both firmware and software based connection
> managers). With this series the following features are supported also for
> USB4 compliant devices:
> 
>   - PCIe tunneling
>   - Display Port tunneling
>   - USB 3.x tunneling
>   - P2P networking (implemented in drivers/net/thunderbolt.c)
>   - Host and device NVM firmware upgrade
> 
> We also add two new sysfs attributes under each device that expose link
> speed and width to userspace. The rest of the userspace ABI stays the same.
> 
> I'm including Linux USB folks as well because USB4 is officially coming
> from USB-IF which puts us on same boat now.
> 
> While I changed the user visible Kconfig string to mention "USB4" (the
> Kconfig option is still CONFIG_THUNDERBOLT), I'm wondering whether we
> should move the whole Thunderbolt driver under drivers/usb/thunderbolt as
> well? 

Looks "interesting", nice work!

I stopped at patch "Add initial support for USB4" as I don't think we
want to add USB4 code to a system that we know does not have it, right?

Everything up to then is just "normal" thunderbolt, and with the
exception of a few minor comments, all look fine to me.

I didn't actually read the USB4 patch just yet, as I figured we needed
to argue about that some more :)

thanks,

greg k-h