[PATCH V5 4/6] doc: ti: k3: Add TIFS Stub documentation

[Dhruva Gole]

Add documentation to briefly explain the role of TIFS Stub in relevant
K3 SoC's.
This also sheds light on why TIFS Stub isn't package with the DM firmware
itself.

Signed-off-by: Dhruva Gole <d-gole at ti.com>
---
 doc/board/ti/k3.rst | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/doc/board/ti/k3.rst b/doc/board/ti/k3.rst
index 67b066a07d3a..c80060662074 100644
--- a/doc/board/ti/k3.rst
+++ b/doc/board/ti/k3.rst
@@ -193,6 +193,17 @@ online
     device resources such as power, clock, interrupts, dma etc. This firmware
     runs on a dedicated or multi-use microcontroller outside the security
     enclave.
+  * **TIFS Stub** - A small piece of code that helps restore the remaining
+    context and resume the TIFS firmware when resuming from Low Power Modes
+    like Suspend-to-RAM/ Deep Sleep. It is loaded into the ATCM (Tightly
+    Coupled Memory 'A' of the DM R5) during DM startup. The reason it isn't
+    merged with DM is because in HS devices we need to sign the tifs-stub with
+    customer key. The DM cannot have a component signed using a customer key
+    because a HS device customer owns the customer key and only customer
+    has the access for the customer key. Since TIFS Stub signing has to happen
+    from the customer side but DM is released by TI, we need to allow binman to
+    sign the TIFS Stub and only then package it alongside other firmwares.
+    This applies only to AM62x, AM62A and AM62P based devices.
 
  OR
 
-- 
2.34.1