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

[Dhruva Gole]

On Jul 17, 2024 at 13:47:19 -0500, Nishanth Menon wrote:
> On 22:18-20240705, Dhruva Gole wrote:
> > 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.
> 
> This implies TI is hiding DM source - we are not. TIFS stub is prop
> binary (the usual issues), but can you rephrase the description above? I
> do not want to go and explicitly list out the devices this section has
> either..

OK.
I was trying to convey was the binary is provided by TI not that its
hidden. But yes I will reword it to say:

.... but DM is released by TI or can be built independently by customers
using the publicly available sources, we need to allow binman......

> 
> Futher, the way it is introduced, did you check the documentation for
> other SoCs? we dont want tifs stub section to punch in for other SoCs
> which dont matter.

Yep, it appears wherever there's include::  ../ti/k3.rst,
I will introduce few more tags between k3_rst_include_start_boot_sources
and k3_rst_include_end_boot_sources to help with this. Does that make
sense?


-- 
Best regards,
Dhruva Gole <d-gole at ti.com>