Re: [Patch 3/5] ACPI: CPPC: support updating epp, auto_sel and {min|max_perf} from sysfs

[Pierre Gondois]

Hello Sumit,

On 2/11/25 11:37, Sumit Gupta wrote:
> Add support to update the CPC registers used for Autonomous
> Performance Level Selection from acpi_cppc sysfs store nodes.
> Registers supported for updation are:
> - Engergy Performance Preference (EPP): energy_perf
> - Autonomous Selection: auto_sel
> - Maximum Performance: max_perf
> - Minimum Performance: min_perf
>
> Also, enable show nodes to read of the following CPC registers:
> - Performance Limited: perf_limited
> - Autonomous Activity Window: auto_activity_window
>
> Signed-off-by: Sumit Gupta <sumitg@xxxxxxxxxx>
> ---
>   drivers/acpi/cppc_acpi.c | 191 ++++++++++++++++++++++++++++++++++++---
>   include/acpi/cppc_acpi.h |   5 +
>   2 files changed, 183 insertions(+), 13 deletions(-)
>
> diff --git a/drivers/acpi/cppc_acpi.c b/drivers/acpi/cppc_acpi.c
> index cc2bf958e84f..c60ad66ece85 100644
> --- a/drivers/acpi/cppc_acpi.c
> +++ b/drivers/acpi/cppc_acpi.c

[...]

>   sysfs_cppc_data(cppc_get_perf_caps, cppc_perf_caps, highest_perf, ro);
>   sysfs_cppc_data(cppc_get_perf_caps, cppc_perf_caps, lowest_perf, ro);
>   sysfs_cppc_data(cppc_get_perf_caps, cppc_perf_caps, nominal_perf, ro);
> @@ -177,9 +304,16 @@ sysfs_cppc_data(cppc_get_perf_caps, cppc_perf_caps, lowest_nonlinear_perf, ro);
>   sysfs_cppc_data(cppc_get_perf_caps, cppc_perf_caps, guaranteed_perf, ro);
>   sysfs_cppc_data(cppc_get_perf_caps, cppc_perf_caps, lowest_freq, ro);
>   sysfs_cppc_data(cppc_get_perf_caps, cppc_perf_caps, nominal_freq, ro);
> +sysfs_cppc_data(cppc_get_perf_caps, cppc_perf_caps, auto_sel, rw);
>   
>   sysfs_cppc_data(cppc_get_perf_fb_ctrs, cppc_perf_fb_ctrs, reference_perf, ro);
>   sysfs_cppc_data(cppc_get_perf_fb_ctrs, cppc_perf_fb_ctrs, wraparound_time, ro);
> +sysfs_cppc_data(cppc_get_perf_fb_ctrs, cppc_perf_fb_ctrs, perf_limited, ro);
> +
> +sysfs_cppc_data(cppc_get_perf_ctrls, cppc_perf_ctrls, min_perf, rw);
> +sysfs_cppc_data(cppc_get_perf_ctrls, cppc_perf_ctrls, max_perf, rw);

IIUC, this means that users can modify the min/max performance levels of the CPU
without having the cpufreq framework notified. Meaning that if a user modifies these
levels, the frequency selection will be done using the initial min/max performance
level.
I think it would be better not allow users to modifies these values directly. Reliying
on existing scaling_min_freq/scaling_max_freq files would be better IMO.

Regards,
Pierre