Merge branch 'update-usb-host-info' into 'master'

Update USB host mode instructions

See merge request Librem5/developer.puri.sm!328

Development_Environment/Boards/HowTo/USB_Access.rst

@@ -18,24 +18,64 @@ composite gadget which provides both serial and networking support.
 Alternate Configuration - USB C Host
 ------------------------------------
 
+.. warning:: Using the board in this mode means that you will lose access to
+             the USB serial console, so it is important to have set up SSH
+             access via Ethernet before following these steps.
+
 In this configuration, USB host mode is used to allow keyboard, mouse and flash
 memory sticks to be connected to the development board.
 
-**Note:** Using the board in this mode means that you will lose access to the
-USB serial console, so it is important to have set up SSH access via Ethernet
-before following these steps.
+The `J5 Create JCA374`_ USB Type-C Multi-Adapter is known to work as a hub and
+power the board using USB Power Delivery.
+
+Follow the instructions for the kernel you are running on the development board.
+
+Linux 4.18
+~~~~~~~~~~
 
- 1. On the target, backup the device tree and copy in the USB host version::
+ #. On the development board, backup the device tree and copy in the USB host
+    version::
 
       cp /boot/dtbs/librem5-evk.dtb /boot/dtbs/librem5-evk.dtb.bak
       cp /boot/dtbs/librem5-evk-usbhost.dtb /boot/dtbs/librem5-evk.dtb
 
- 2. Attach a USB C hub to the development board.
- 3. Attach power to the USB C hub.
- 4. Plug in USB devices and they should appear in the output of the ``dmesg``
+ #. Attach a USB C hub to the development board.
+ #. Attach power to the USB C hub.
+ #. Plug in USB devices and they should appear in the output of the ``dmesg``
+    and ``lsusb`` tools.
+
+Linux 5.2
+~~~~~~~~~
+
+The following steps will work for the specific version of the kernel you are
+using. When the kernel is updated, you will need to perform these steps again.
+
+ #. On the development board, backup the device tree binary file::
+
+      sudo cp /boot/dtbs/`uname -r`/imx8mq-librem5-devkit.dtb /boot/dtbs/`uname -r`/imx8mq-librem5-devkit.dtb.bak
+
+ #. Extract the device tree sources from the binary::
+
+      dtc /boot/dtbs/`uname -r`/imx8mq-librem5-devkit.dtb > /tmp/imx8mq-librem5-devkit.dts
+
+ #. Find this line in the newly created ``/tmp/imx8mq-librem5-devkit.dts``::
+
+      dr_mode = "otg";
+
+    Change it to this::
+
+      dr_mode = "host";
+
+    Save the file.
+
+ #. Generate a new device tree binary file::
+
+      sudo dtc /tmp/imx8mq-librem5-devkit.dts > /boot/dtbs/`uname -r`/imx8mq-librem5-devkit.dtb
+
+ #. Attach a USB C hub to the development board.
+ #. Attach power to the USB C hub.
+ #. Plug in USB devices and they should appear in the output of the ``dmesg``
     and ``lsusb`` tools.
 
-The `J5 Create JCA374`_ USB Type-C Multi-Adapter is known to work as a hub and
-power the board using USB Power Delivery.
 
 .. include:: /links.txt