Re: Procedures adding new CPUs in sbsa-ref

From: "Alex Bennée" <alex.bennee@linaro.org>
To: Itaru Kitayama <itaru.kitayama@gmail.com>
Cc: Peter Maydell <peter.maydell@linaro.org>,
	Leif Lindholm <leif@nuviainc.com>,
	qemu-devel@nongnu.org, Radoslaw Biernacki <rad@semihalf.com>
Subject: Re: Procedures adding new CPUs in sbsa-ref
Date: Mon, 11 Apr 2022 16:16:54 +0100	[thread overview]
Message-ID: <87a6cr1w7x.fsf@linaro.org> (raw)
In-Reply-To: <CANW9uyt5UDNrygX_TS9FBDb5pJdJLkHAtHqDFEoyg1U0Mgz0Ug@mail.gmail.com>

Itaru Kitayama <itaru.kitayama@gmail.com> writes:

> Good point; however per the SBSA specification, DEN0029F, there's the
> PE architecture requirement at
> each level from 1 to 7, so now I am wondering whether supporting
> cortex-a57 and a72 are good enough to
> set up a fully SBSA level 7 compliant "board" in QMEU.

Not currently - we are working on cortex-a76/neoverse-n1 which will
provide a v8.2 baseline for sbsa-ref. See:

  Subject: [PATCH 00/16] target/arm: Implement features Debugv8p4, RAS, IESB
  Date: Fri,  8 Apr 2022 17:07:26 -0700
  Message-Id: <20220409000742.293691-1-richard.henderson@linaro.org>

and:

  Subject: [PATCH 0/7] target/arm: More trivial features, A76, N1
  Date: Sat,  9 Apr 2022 22:57:18 -0700
  Message-Id: <20220410055725.380246-1-richard.henderson@linaro.org>

which are stepping stones to those concrete models. Please review if you
can. 

> Also, the 'max'
> is there, but does not boot.

Generally the firmware has to be built with the knowledge of what system
it is running on so will generally fall over if run on a different CPU
feature set. However I believe Leif had a firmware branch which attempts
to work with -cpu max by doing proper ID register probing before using
features. However -cpu max is very a moving feast which is why there is
a push for the concrete CPU types.

I believe there is a proposal for a versioned sbsa-ref model which will
step of the default CPU for higher levels.

>
> Itaru.
>
> On Sat, Apr 9, 2022 at 12:04 AM Peter Maydell <peter.maydell@linaro.org> wrote:
>>
>> On Fri, 8 Apr 2022 at 15:59, Itaru Kitayama <itaru.kitayama@gmail.com> wrote:
>> > I'd like to add a64fx cpu to the sbsa-ref board, if there's a quick and dirty
>> > way of completing that, advice from the  maintainers is greatly appreciated.
>>
>> I have cc'd the sbsa-ref maintainers (as listed in the MAINTAINERS file).
>>
>> However, I'm not sure why you want to add the a64fx CPU to this
>> board model? The sbsa-ref board is intended as a platform for
>> developing firmware that runs on Server Base System Architecture
>> hardware, so it deliberately doesn't have support for every CPU
>> type QEMU implements.
>>
>> thanks
>> -- PMM

-- 
Alex Bennée