Re: [RFC PATCH 17/22] thunderbolt: Add initial support for USB4 - Greg Kroah-Hartman

From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To: Mika Westerberg <mika.westerberg@linux.intel.com>
Cc: linux-usb@vger.kernel.org,
	Andreas Noever <andreas.noever@gmail.com>,
	Michael Jamet <michael.jamet@intel.com>,
	Yehezkel Bernat <YehezkelShB@gmail.com>,
	Rajmohan Mani <rajmohan.mani@intel.com>,
	Nicholas Johnson <nicholas.johnson-opensource@outlook.com.au>,
	Lukas Wunner <lukas@wunner.de>,
	Alan Stern <stern@rowland.harvard.edu>,
	Mario.Limonciello@dell.com,
	Anthony Wong <anthony.wong@canonical.com>,
	linux-kernel@vger.kernel.org
Subject: Re: [RFC PATCH 17/22] thunderbolt: Add initial support for USB4
Date: Tue, 1 Oct 2019 14:47:48 +0200	[thread overview]
Message-ID: <20191001124748.GH2954373@kroah.com> (raw)
In-Reply-To: <20191001113830.13028-18-mika.westerberg@linux.intel.com>

On Tue, Oct 01, 2019 at 02:38:25PM +0300, Mika Westerberg wrote:
> USB4 is a public spec based on Thunderbolt protocol. There are some
> differences in register layouts and flows. In addition to PCIe and DP
> tunneling, USB4 supports tunneling of USB 3.x. USB4 is also backward
> compatible with Thunderbolt 3 (and older generations but the spec only
> talks about 3rd generation). USB4 compliant devices can be identified by
> checking USB4 version field in router configuration space.
> 
> This patch adds initial support for USB4 compliant hosts and devices
> which enables following features provided by the existing functionality
> in the driver:
> 
>   - PCIe tunneling
>   - Display Port tunneling
>   - Host and device NVM firmware upgrade
>   - P2P networking
> 
> This brings the USB4 support to the same level that we already have for
> Thunderbolt 1, 2 and 3 devices.
> 
> Note the spec talks about host and device "routers" but in the driver we
> still use term "switch" in most places. Both can be used interchangeably.
> 
> This also updates the Kconfig entry accordingly.
> 
> Co-developed-by: Rajmohan Mani <rajmohan.mani@intel.com>
> Signed-off-by: Rajmohan Mani <rajmohan.mani@intel.com>
> Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>
> ---
>  drivers/thunderbolt/Kconfig   |   9 +-
>  drivers/thunderbolt/Makefile  |   2 +-
>  drivers/thunderbolt/eeprom.c  |  53 ++-
>  drivers/thunderbolt/nhi.c     |   3 +
>  drivers/thunderbolt/nhi.h     |   2 +
>  drivers/thunderbolt/switch.c  | 384 +++++++++++++-----
>  drivers/thunderbolt/tb.c      |  20 +-
>  drivers/thunderbolt/tb.h      |  36 ++
>  drivers/thunderbolt/tb_regs.h |  36 +-
>  drivers/thunderbolt/tunnel.c  |  10 +-
>  drivers/thunderbolt/usb4.c    | 722 ++++++++++++++++++++++++++++++++++
>  drivers/thunderbolt/xdomain.c |   6 +
>  12 files changed, 1162 insertions(+), 121 deletions(-)
>  create mode 100644 drivers/thunderbolt/usb4.c
> 
> diff --git a/drivers/thunderbolt/Kconfig b/drivers/thunderbolt/Kconfig
> index fd9adca898ff..8193ec310bae 100644
> --- a/drivers/thunderbolt/Kconfig
> +++ b/drivers/thunderbolt/Kconfig
> @@ -1,6 +1,6 @@
>  # SPDX-License-Identifier: GPL-2.0-only
>  menuconfig THUNDERBOLT
> -	tristate "Thunderbolt support"
> +	tristate "USB4 (Thunderbolt) support"
>  	depends on PCI
>  	depends on X86 || COMPILE_TEST
>  	select APPLE_PROPERTIES if EFI_STUB && X86
> @@ -9,9 +9,10 @@ menuconfig THUNDERBOLT
>  	select CRYPTO_HASH
>  	select NVMEM
>  	help
> -	  Thunderbolt Controller driver. This driver is required if you
> -	  want to hotplug Thunderbolt devices on Apple hardware or on PCs
> -	  with Intel Falcon Ridge or newer.
> +	  USB4 (Thunderbolt) driver. USB4 is the public spec based on
> +	  Thunderbolt 3 protocol. This driver is required if you want to
> +	  hotplug Thunderbolt and USB4 compliant devices on Apple
> +	  hardware or on PCs with Intel Falcon Ridge or newer.

Wait, did "old" thunderbolt just get re-branded as USB4?

Because if I have an "old" laptop that needs Thunderbolt support, how am
I going to know it is now called USB4 instead?

Shouldn't there just be a new USB4 option that only enables/builds the
USB4 stuff if selected?  Why would I want all of this additional code on
my old system if it's not going to do anything at all?

Or am I confused?

thanks,

greg k-h