Re: [PATCH 1/1] hw/arm/sbsa-ref.c: Start APs powered off

[Peter Maydell <peter.maydell@linaro.org>]

On Mon, 2 Jan 2023 at 15:46, Rebecca Cran <rebecca@quicinc.com> wrote:
>
> For the SBSA-REF machine start all APs in the powered-off state.
> This reduces host CPU usage until PSCI_CPU_ON is called when the APs
> are needed.
>
> Signed-off-by: Rebecca Cran <rebecca@quicinc.com>
> ---
>  hw/arm/sbsa-ref.c | 6 ++++++
>  1 file changed, 6 insertions(+)
>
> diff --git a/hw/arm/sbsa-ref.c b/hw/arm/sbsa-ref.c
> index 4bb444684f40..cf0af35c7807 100644
> --- a/hw/arm/sbsa-ref.c
> +++ b/hw/arm/sbsa-ref.c
> @@ -753,6 +753,12 @@ static void sbsa_ref_init(MachineState *machine)
>                                      &error_abort);
>          }
>
> +        /* Configure all APs to be powered off at start */
> +        if (n != 0 && object_property_find(cpuobj, "start-powered-off")) {
> +            object_property_set_bool(cpuobj, "start-powered-off",
> +                                     true, &error_abort);
> +        }
> +
>          object_property_set_link(cpuobj, "memory", OBJECT(sysmem),
>                                   &error_abort);

This board disables QEMU's own PSCI implementation and relies on
a guest EL3 firmware to provide PSCI. So how will that EL3
firmware implement the "power on" to bring up the secondaries?
QEMU has the APIs to allow implementation of a model of a
hardware power controller (target/arm/arm-powerctl.h) but
as far as I can see the sbsa-ref board doesn't yet implement
one, so if you start the CPUs in the powered-off state there's
no way for them ever to be powered on.

thanks
-- PMM