Re: [PATCH 1/2] ACPI: processor: idle: Return an error if both P_LVL{2,3} idle states are invalid

["Zhang, Rui" <rui.zhang@intel.com>]

On Fri, 2025-03-28 at 15:30 +0100, Giovanni Gherdovich wrote:
> Prior to commit 496121c02127e9c460b436244c38260b044cc45a ("ACPI:
> processor:
> idle: Allow probing on platforms with one ACPI C-state"), the
> acpi_idle
> driver wouldn't load on systems without a valid C-State at least as
> deep
> as C2. The behavior was desirable for guests on hypervisors such as
> VMWare
> ESXi, which by default don't have the _CST ACPI method, and set the
> C2 and
> C3 latencies to 101 and 1001 microseconds respectively via the FADT,
> to
> signify they're unsupported.
> 
> Since the above change though, these virtualized deployments end up
> loading
> acpi_idle, and thus entering the default C1 C-State set by
> acpi_processor_get_power_info_default(); this is undesirable for a
> system
> that's communicating to the OS it doesn't want C-States (missing
> _CST, and
> invalid C2/C3 in FADT).
> 
> Make acpi_processor_get_power_info_fadt() return ENODEV in that case,
> so
> that acpi_processor_get_cstate_info() exits early and doesn't set
> pr->flags.power = 1.
> 
> Fixes: 496121c02127 ("ACPI: processor: idle: Allow probing on
> platforms with one ACPI C-state")
> Signed-off-by: Giovanni Gherdovich <ggherdovich@suse.cz>

LGTM.

Reviewed-by: Zhang Rui <rui.zhang@intel.com>

-rui
> ---
>  drivers/acpi/processor_idle.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/drivers/acpi/processor_idle.c
> b/drivers/acpi/processor_idle.c
> index 586cc7d1d8aa..b181f7fc2090 100644
> --- a/drivers/acpi/processor_idle.c
> +++ b/drivers/acpi/processor_idle.c
> @@ -268,6 +268,10 @@ static int
> acpi_processor_get_power_info_fadt(struct acpi_processor *pr)
>  			 ACPI_CX_DESC_LEN, "ACPI P_LVL3 IOPORT
> 0x%x",
>  			 pr->power.states[ACPI_STATE_C3].address);
>  
> +	if (!pr->power.states[ACPI_STATE_C2].address &&
> +	    !pr->power.states[ACPI_STATE_C3].address)
> +		return -ENODEV;
> +
>  	return 0;
>  }
>