Re: [PATCH 1/1] docs: sbsa: update specs, add dt note

[Marcin Juszkiewicz]

W dniu 28.03.2024 o 16:43, Peter Maydell pisze:
> On Tue, 26 Mar 2024 at 09:58, Marcin Juszkiewicz
> <marcin.juszkiewicz@linaro.org> wrote:
> > Hardware of sbsa-ref board is nowadays defined by both BSA and SBSA
> > specifications. Then BBR defines firmware interface.
> >
> > Added note about DeviceTree data passed from QEMU to firmware. It is
> > very minimal and provides only data we use in firmware.
> >
> > Added NUMA information to list of things reported by DeviceTree.
> >
> > Signed-off-by: Marcin Juszkiewicz <marcin.juszkiewicz@linaro.org>
> > ---
> >   docs/system/arm/sbsa.rst | 37 ++++++++++++++++++++++++++++---------
> >   1 file changed, 28 insertions(+), 9 deletions(-)
> >
> > diff --git a/docs/system/arm/sbsa.rst b/docs/system/arm/sbsa.rst
> > index bca61608ff..d4d1f2efe3 100644
> > --- a/docs/system/arm/sbsa.rst
> > +++ b/docs/system/arm/sbsa.rst

> > +Note
> > +''''
> > +
> > +QEMU provides us with minimal information about hardware platform using
>
> s/us/the guest EL3 firmware/  (or whatever other term you want to
> use to describe the guest software that reads the dt).

Thanks, fixed.

> > +minimalistic devicetree. This is not a Linux devicetree. It is not even a
> > +firmware devicetree.
> > +
> > +It is information passed from QEMU to describe the information a hardware
> > +platform would have other mechanisms to discover at runtime, that are affected
> > +by the QEMU command line.
>
>
> Might want to say also
>   Guest EL3 firmware does not pass this devicetree on to later
>   components of the software stack.
> ?

This is a matter of what firmware stack QEMU user will run. TF-A (our 
current "guest EL3 firmware") passed devicetree to later components of 
the software stack. We just stopped using it in EDK2. But if someone 
would like to run U-Boot or other firmware then both SMC and DT will 
wait for them.

> > +
> > +Ultimately this devicetree will be replaced by IPC calls to an emulated SCP.
> > +And when we do that, we won't then have to rewrite Normal world firmware to
> > +cope.
>
> I would drop the last sentence here, and use "may" instead of "will".

Done.

> > +
> >   DeviceTree information
> >   ''''''''''''''''''''''
> >
> > -The devicetree provided by the board model to the firmware is not intended
> > -to be a complete compliant DT. It currently reports:
> > +The devicetree reports:
> >
> >      - CPUs
> >      - memory
> >      - platform version
> >      - GIC addresses
> > +   - NUMA node id for CPUs and memory
>
> Otherwise looks good to me, and the updates to the spec URLs
> are particularly helpful. As a docs change I'd be happy
> to take it into 9.0 (at least before rc2) if some other
> sbsa-ref-knowledgeable person wants to either review or ack it.
> (But it's also OK if it misses 9.0 and goes into 9.1.)

OK.