On Wed, Jun 29, 2022 at 10:04 PM Mario Limonciello
<mario.limonciello@xxxxxxx> 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 a dedicated
> MSR from `X86_FEATURE_CPPC`, use that to enable this feature rather
> than requiring the `_OSC` on platforms with a dedicated MSR.
>
> If there is additional breakage on the shared memory designs also
> missing this _OSC, additional follow up changes may be needed.
>
> Fixes: 72f2ecb7ece7 ("Set CPPC _OSC bits for all and when CPPC_LIB is supported")
> Reported-by: Perry Yuan <perry.yuan@xxxxxxx>
> Signed-off-by: Mario Limonciello <mario.limonciello@xxxxxxx>
I'm still concerned about the possible cases in which there is _CPC,
but it returns garbage, because the firmware thinks that the OS will
not use _CPC due to the _OSC handshake.
> ---
> v1->v2:
> * Make the code easier to follow (suggested by Rafael)
> * Update commit message to reflect this is only fixing the MSR case
> and that any other breakage from 72f2ecb7ece7 will need additional
> follow ups
> drivers/acpi/cppc_acpi.c | 13 +++++++++----
> 1 file changed, 9 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/acpi/cppc_acpi.c b/drivers/acpi/cppc_acpi.c
> index 903528f7e187..cc154519c608 100644
> --- a/drivers/acpi/cppc_acpi.c
> +++ b/drivers/acpi/cppc_acpi.c
> @@ -629,7 +629,15 @@ static bool is_cppc_supported(int revision, int num_ent)
> return false;
> }
>
> - return true;
> + if (!osc_sb_cppc_not_supported)
> + return true;
> +
> + pr_debug("Firmware missing _OSC support\n");
> +#ifdef CONFIG_X86
> + return boot_cpu_has(X86_FEATURE_CPPC);
So can you please add an additional X86_VENDOR_AMD check to the above?
> +#else
> + return false;
> +#endif
> }
>
> /*
> @@ -684,9 +692,6 @@ 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);
> --
> 2.25.1
>
