thunderbolt: Update NVM firmware upgrade documentation

Update guide about firmware upgrade of Thunderbolt devices, replacing
outdated recommendations with the use of modern "fwupd" tool.

Signed-off-by: Alan Borzeszkowski <alan.borzeszkowski@linux.intel.com>
Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>

Documentation/admin-guide/thunderbolt.rst

@@ -203,10 +203,10 @@ host controller or a device, it is important that the firmware can be
 upgraded to the latest where possible bugs in it have been fixed.
 Typically OEMs provide this firmware from their support site.
 
-There is also a central site which has links where to download firmware
-for some machines:
-
-  `Thunderbolt Updates <https://thunderbolttechnology.net/updates>`_
+Currently, recommended method of updating firmware is through "fwupd" tool.
+It uses LVFS (Linux Vendor Firmware Service) portal by default to get the
+latest firmware from hardware vendors and updates connected devices if found
+compatible. For details refer to: https://github.com/fwupd/fwupd.
 
 Before you upgrade firmware on a device, host or retimer, please make
 sure it is a suitable upgrade. Failing to do that may render the device
@@ -215,18 +215,40 @@ tools!
 
 Host NVM upgrade on Apple Macs is not supported.
 
-Once the NVM image has been downloaded, you need to plug in a
-Thunderbolt device so that the host controller appears. It does not
-matter which device is connected (unless you are upgrading NVM on a
-device - then you need to connect that particular device).
+Fwupd is installed by default. If you don't have it on your system, simply
+use your distro package manager to get it.
+
+To see possible updates through fwupd, you need to plug in a Thunderbolt
+device so that the host controller appears. It does not matter which
+device is connected (unless you are upgrading NVM on a device - then you
+need to connect that particular device).
 
 Note an OEM-specific method to power the controller up ("force power") may
 be available for your system in which case there is no need to plug in a
 Thunderbolt device.
 
-After that we can write the firmware to the non-active parts of the NVM
-of the host or device. As an example here is how Intel NUC6i7KYK (Skull
-Canyon) Thunderbolt controller NVM is upgraded::
+Updating firmware using fwupd is straightforward - refer to official
+readme on fwupd github.
+
+If firmware image is written successfully, the device shortly disappears.
+Once it comes back, the driver notices it and initiates a full power
+cycle. After a while device appears again and this time it should be
+fully functional.
+
+Device of interest should display new version under "Current version"
+and "Update State: Success" in fwupd's interface.
+
+Upgrading firmware manually
+---------------------------------------------------------------
+If possible, use fwupd to updated the firmware. However, if your device OEM
+has not uploaded the firmware to LVFS, but it is available for download
+from their side, you can use method below to directly upgrade the
+firmware.
+
+Manual firmware update can be done with 'dd' tool. To update firmware
+using this method, you need to write it to the non-active parts of NVM
+of the host or device. Example on how to update Intel NUC6i7KYK
+(Skull Canyon) Thunderbolt controller NVM::
 
   # dd if=KYK_TBT_FW_0018.bin of=/sys/bus/thunderbolt/devices/0-0/nvm_non_active0/nvmem
 
@@ -235,10 +257,8 @@ upgrade process as follows::
 
   # echo 1 > /sys/bus/thunderbolt/devices/0-0/nvm_authenticate
 
-If no errors are returned, the host controller shortly disappears. Once
-it comes back the driver notices it and initiates a full power cycle.
-After a while the host controller appears again and this time it should
-be fully functional.
+If no errors are returned, device should behave as described in previous
+section.
 
 We can verify that the new NVM firmware is active by running the following
 commands::