Re: [RFC PATCH] docs: add some notes on the sbsa-ref machine

[Alex Bennée]

Leif Lindholm <leif@nuviainc.com> writes:

> On Tue, Nov 03, 2020 at 10:47:10 +0000, Alex Bennée wrote:
>> We should at least document what this machine is about.
>
> Thanks!
> (comments below)
>
>> Cc: Graeme Gregory <graeme@nuviainc.com>
>> Cc: Leif Lindholm <leif@nuviainc.com>
>> Cc: Hongbo Zhang <hongbo.zhang@linaro.org>
>> Cc: Shashi Mallela <shashi.mallela@linaro.org>
>> Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
>> ---
>>  docs/system/arm/sbsa.rst   | 30 ++++++++++++++++++++++++++++++
>>  docs/system/target-arm.rst |  1 +
>>  2 files changed, 31 insertions(+)
>>  create mode 100644 docs/system/arm/sbsa.rst
>> 
>> diff --git a/docs/system/arm/sbsa.rst b/docs/system/arm/sbsa.rst
>> new file mode 100644
>> index 0000000000..a47c9360de
>> --- /dev/null
>> +++ b/docs/system/arm/sbsa.rst
>> @@ -0,0 +1,30 @@
>> +Arm Server Base System Architecture Reference board (``sbsa-ref``)
>> +==================================================================
>> +
>> +While the `virt` board is a generic board platform that doesn't match
>> +any real hardware the `sbsa-ref` board intends to look like real
>> +hardware. The `Server Base System Architecture
>> +<https://developer.arm.com/documentation/den0029/latest>` defines a
>> +minimum base line of hardware support and importantly how the firmware
>> +reports that to any operating system. It is a static system that
>> +reports a very minimal DT to the firmware for command line input to
>> +the firmware.
>
> I think you mean the right thing, but ...
> "a very minimal DT to the firmware for non-discoverable information
>  about components affected by the qemu command line"
>  (i.e. cpus and memory)
>
>> As a result it must have a firmware specifically built
>> +to expect a certain hardware layout (as you would in a real machine).
>> +
>> +It is intended to be a machine for developing firmware and testing
>> +standards compliance with operating systems.
>> +
>> +Supported devices
>> +"""""""""""""""""
>> +
>> +The sbsa-ref board supports:
>> +
>> +  - A configurable number of Cortex-A57 cpus
>> +  - GIC version 3
>
> The intent was always for sbsa-ref to be tracking SBSA development, so
> I wonder whether we should be documenting specific versions of cpu and
> gic (and then keep remembering to update the docs).
> My short-term plan was to swap the a57 for "max", but
> documentation-wise, could we just say "number of aarch64 cpus"?
> Could we refer to the gic as "latest supported emulated"?

I'm not sure we want a movable feast... shouldn't we at least provide
compatibility for older variations? -cpu max is useful but you can get
new features coming out of the blue.

-- 
Alex Bennée