fix(PRU-ICSS): Update cut thru documentation for switch mode

Cut thru documentation has a gap on the order of steps in which
the cut thru needs to be enabled. This commit fixes it by adding
the recommended steps order to follow for enabling cut thru.

Signed-off-by: Meghana Malladi <[email protected]>

Author: MeghanaMalladiTI

source/linux/Foundational_Components/PRU-ICSS/Linux_Drivers/PRU_ICSSG_Ethernet_Switch.rst

@@ -129,9 +129,6 @@ Assuming eth1 and eth2 are the active ports of ICSSG1 on AM64xx-EVM, to enable c
 
 .. code-block:: console
 
-   ip link set eth1 down
-   ip link set eth2 down
-
    # To enable cut thru for slice0 q0
    devlink dev param set platform/icssg1-eth name cut_thru value 1 cmode runtime
 
@@ -144,9 +141,6 @@ Assuming eth1 and eth2 are the active ports of ICSSG1 on AM64xx-EVM, to enable c
    # To enable cut thru for slice0 q0, q1 and slice1 q0, q1
    devlink dev param set platform/icssg1-eth name cut_thru value 771 cmode runtime
 
-   ip link set eth1 up
-   ip link set eth2 up
-
 To show the current cut through status, run the below command,
 
 .. code-block:: console
@@ -166,6 +160,33 @@ To disable cut through on all queues
 
    devlink dev param set platform/icssg1-eth name cut_thru value 0 cmode runtime
 
+.. note::
+
+    Cut thru value should be set up first before enabling switch mode to ensure that
+    cut thru is working properly. This order ensures that firmware is loaded with the
+    expected cut thru value.
+
+Below steps order is suggested for enabling cut thru in switch mode
+
+.. code-block:: console
+
+   # Enable Cut-through
+   # Will only take affect if a firmware reload occurs
+   # To enable cut thru for slice0 q0, q1 and slice1 q0, q1
+   devlink dev param set platform/icssg1 name cut_thru value 771 cmode runtime
+
+   # Enable Switch Mode
+   # Will reload the firmware so no need to bring links down and back up again
+   # Ensure that switch mode is enabled AFTER cut-through
+   ip link add name bridge0 type bridge
+   ip link set dev eth1 master bridge0
+   ip link set dev eth2 master bridge0
+   ip link set dev bridge0 up
+   bridge vlan add dev bridge0 vid 1 pvid untagged self
+   sleep 2
+   # To check cut-through configuration
+   devlink dev param show platform/icssg1-eth name cut_thru
+
 PTP
 """
 PTP can be run during switch mode. To run PTP in switch mode, 3 AM64x EVMs need to be connected with middle EVM acting as the switch. Use the following ptp config file on all slave EVMs. For Master EVM, priority1 filed needs to be changed.