Re: [PATCH] hw/arm/virt: Default to architecture appropriate CPU

[Punit Agrawal]

Hi Peter,

Thanks for the quick feedback and the background. 

Peter Maydell <peter.maydell@linaro.org> writes:

> On Thu, 20 Aug 2020 at 05:55, Punit Agrawal
> <punit1.agrawal@toshiba.co.jp> wrote:
>>
>> The default_cpu_type for the Virt machine is set to "cortex-a15" for
>> both the arm (qemu-system-arm) and aarch64 (qemu-system-aarch64)
>> targets.
>>
>> As a result, starting the aarch64 target with "-machine virt" defaults
>> to booting with a Arm v7 cpu which is counter to
>> expectation. Debugging the issue is further hampered by lack of any
>> output from a supplied arm64 firmware as it is now running on the
>> wrong CPU type.
>>
>> Fix this by defaulting to the "max" capability CPU for the target
>> architecture. After the patch both the arm and aarch64 qemu default to
>> the equivalent of passing "-cpu max".
>
> Hi; this kind of thing has been suggested in the past several times.
> Generally we've taken the view that we prefer:
>  * not to make changes that would break pre-existing command lines
>  * to maintain the general behaviour that a command line used
>    with qemu-system-arm will also work with qemu-system-aarch64

It did feel like too low hanging a fruit to not have been looked into
before. Generally the above makes sense - though defaulting
qemu-system-aarch64 to start with a 32bit cpu is stretching the above
view too far I think.

> It is certainly true that these days the default CPU type for
> virt is not what most users want, though.

I do understand it's a balancing act when it comes to changing user
visible options. But it's worth revisiting the choice if most users
would prefer otherwise.

Thanks,

Punit