On Thu, Feb 24, 2022 at 09:12:55PM -0600, Mario Limonciello wrote:
> When `osc_pc_lpi_support_confirmed` is set through `_OSC` and `_LPI` is
> populated then the cpuidle driver assumes that LPI is fully functional.
>
> However currently the kernel only provides architectural support for LPI
> on ARM. This leads to high power consumption on X86 platforms that
> otherwise try to enable LPI.
>
> So probe whether or not LPI support is implemented before enabling LPI in
> the kernel. This is done by overloading `acpi_processor_ffh_lpi_probe` to
> check whether it returns `-EOPNOTSUPP`. It also means that all future
> implementations of `acpi_processor_ffh_lpi_probe` will need to follow
> these semantics as well.
>
> Signed-off-by: Mario Limonciello <mario.limonciello@xxxxxxx>
> ---
> drivers/acpi/processor_idle.c | 15 ++++++++++-----
> 1 file changed, 10 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/acpi/processor_idle.c b/drivers/acpi/processor_idle.c
> index f8e9fa82cb9b..0092fd479527 100644
> --- a/drivers/acpi/processor_idle.c
> +++ b/drivers/acpi/processor_idle.c
> @@ -1080,6 +1080,11 @@ static int flatten_lpi_states(struct acpi_processor *pr,
> return 0;
> }
>
> +int __weak acpi_processor_ffh_lpi_probe(unsigned int cpu)
> +{
> + return -EOPNOTSUPP;
> +}
> +
> static int acpi_processor_get_lpi_info(struct acpi_processor *pr)
> {
> int ret, i;
> @@ -1094,6 +1099,11 @@ static int acpi_processor_get_lpi_info(struct acpi_processor *pr)
> if (!acpi_has_method(handle, "_LPI"))
> return -EINVAL;
>
> + /* make sure our architecture has support */
> + ret = acpi_processor_ffh_lpi_probe(pr->id);
> + if (ret == -EOPNOTSUPP)
> + return ret;
> +
You can do this check first, before even checking osc_pc_lpi_support_confirmed
and looking for _LPI method IMO as they are not useful if arch doesn't support
handling LPIs.
Either way,
Reviewed-by: Sudeep Holla <sudeep.holla@xxxxxxx>
--
Regards,
Sudeep
