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SubjectRe: [PATCH] ACPI: CPPC: Don't require _OSC if X86_FEATURE_CPPC is supported
On Mon, Jun 27, 2022 at 6:58 PM Mario Limonciello
<mario.limonciello@amd.com> wrote:
>
> commit 72f2ecb7ece7 ("ACPI: bus: Set CPPC _OSC bits for all and
> when CPPC_LIB is supported") added support for claiming to
> support CPPC in _OSC on non-Intel platforms.
>
> This unfortunately caused a regression on a vartiety of AMD
> platforms in the field because a number of AMD platforms don't set
> the `_OSC` bit 5 or 6 to indicate CPPC or CPPC v2 support.
>
> As these AMD platforms already claim CPPC support via `X86_FEATURE_CPPC`,
> use this enable this feature rather than requiring the `_OSC`.
>
> Fixes: 72f2ecb7ece7 ("Set CPPC _OSC bits for all and when CPPC_LIB is supported")
> Reported-by: Perry Yuan <perry.yuan@amd.com>
> Signed-off-by: Mario Limonciello <mario.limonciello@amd.com>
> ---
> drivers/acpi/cppc_acpi.c | 12 +++++++++---
> 1 file changed, 9 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/acpi/cppc_acpi.c b/drivers/acpi/cppc_acpi.c
> index 903528f7e187..5463e6309b9a 100644
> --- a/drivers/acpi/cppc_acpi.c
> +++ b/drivers/acpi/cppc_acpi.c
> @@ -629,6 +629,15 @@ static bool is_cppc_supported(int revision, int num_ent)
> return false;
> }
>
> + if (osc_sb_cppc_not_supported) {
> + pr_debug("Firmware missing _OSC support\n");
> +#ifdef CONFIG_X86
> + return boot_cpu_has(X86_FEATURE_CPPC);
> +#else
> + return false;
> +#endif

What about doing

if (osc_sb_cppc_not_supported) {
pr_debug("Firmware missing _OSC support\n");
return IS_ENABLED(CONFIG_X86) && boot_cpu_has(X86_FEATURE_CPPC);
}

instead for the sake of reducing #ifdeffery?

Also, this is somewhat risky, because even if the given processor has
X86_FEATURE_CPPC set, the platform may still not want to expose CPPC
through ACPI. How's that going to work after this change?


> + }
> +
> return true;
> }
>
> @@ -684,9 +693,6 @@ int acpi_cppc_processor_probe(struct acpi_processor *pr)
> acpi_status status;
> int ret = -ENODATA;
>
> - if (osc_sb_cppc_not_supported)
> - return -ENODEV;
> -
> /* Parse the ACPI _CPC table for this CPU. */
> status = acpi_evaluate_object_typed(handle, "_CPC", NULL, &output,
> ACPI_TYPE_PACKAGE);
> --
> 2.34.1
>

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