Re: [Minios-devel] [UNIKRAFT PATCHv4 35/43] plat/common: Implement CPU suspend for arm64

[Julien Grall <julien.grall@xxxxxxx>]

Hi Wei,

On 06/07/18 10:03, Wei Chen wrote:
> Using PSCI despatch function to call PSCI_CPU_SUSPEND
> function to halt CPU.
>
> Signed-off-by: Wei Chen <Wei.Chen@xxxxxxx>
> ---
>   plat/common/arm/cpu_native.c        | 44 +++++++++++++++++++++++++++++
>   plat/common/include/arm/arm64/cpu.h |  2 ++
>   2 files changed, 46 insertions(+)
>   create mode 100644 plat/common/arm/cpu_native.c
>
> diff --git a/plat/common/arm/cpu_native.c b/plat/common/arm/cpu_native.c
> new file mode 100644
> index 0000000..07548bf
> --- /dev/null
> +++ b/plat/common/arm/cpu_native.c
> @@ -0,0 +1,44 @@
> +/* SPDX-License-Identifier: BSD-3-Clause */
> +/*
> + * Authors: Wei Chen <wei.chen@xxxxxxx>
> + *
> + * Copyright (c) 2018, Arm Ltd., All rights reserved.
> + *
> + * Redistribution and use in source and binary forms, with or without
> + * modification, are permitted provided that the following conditions
> + * are met:
> + *
> + * 1. Redistributions of source code must retain the above copyright
> + *    notice, this list of conditions and the following disclaimer.
> + * 2. Redistributions in binary form must reproduce the above copyright
> + *    notice, this list of conditions and the following disclaimer in the
> + *    documentation and/or other materials provided with the distribution.
> + * 3. Neither the name of the copyright holder nor the names of its
> + *    contributors may be used to endorse or promote products derived from
> + *    this software without specific prior written permission.
> + *
> + * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
> + * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
> + * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
> + * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE
> + * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
> + * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
> + * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
> + * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
> + * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
> + * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
> + * POSSIBILITY OF SUCH DAMAGE.
> + *
> + * THIS HEADER MAY NOT BE EXTRACTED OR MODIFIED IN ANY WAY.
> + */
> +
> +#include <arm/cpu.h>
> +#include <arm/cpu_defs.h>
> +
> +void halt(void)
Looking at the usage of halt, I think PSCI CPU suspend is too expensive 
for brief idling.
I am not entirely sure of the semantic expected, but it looks like "wfi" 
would be more suitable here.
> +{
> +       if (psci_method == PSCI_METHOD_HVC)
> +               psci_hvc_call(PSCI_FNID_CPU_SUSPEND);
> +       else if (psci_method == PSCI_METHOD_SMC)
> +               psci_smc_call(PSCI_FNID_CPU_SUSPEND);
Regardless my comment above, I don't think this code follow the PSCI 
spec. CPU_SUSPEND takes another parameter that is left unknown. Also,
Furthermore, you may want to introduce a function pointer and detect at 
initialization which call you want to use rather than checking in every 
function.
Lastly, in case of non-PSCI platform function will just do nothing. This 
looks slightly strange.
Cheers,

--
Julien Grall

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