Re: [PATCH v2 2/2] PM / QoS: Restore DEV_PM_QOS_MIN/MAX_FREQUENCY

[Matthias Kaehlcke <mka@chromium.org>]

Hi Leonard,

On Tue, Nov 19, 2019 at 12:56:43AM +0200, Leonard Crestez wrote:
> Support for adding per-device frequency limits was removed in commit
> 2aac8bdf7a0f ("PM: QoS: Drop frequency QoS types from device PM QoS")
> after cpufreq switched to use a new "freq_constraints" construct.
> 
> Restore support for per-device freq limits but base this upon
> freq_constraints. This is primarily meant to be used by the devfreq
> subsystem.
> 
> This removes the "static" marking on freq_qos_apply but does not export
> it for modules.
> 
> Signed-off-by: Leonard Crestez <leonard.crestez@nxp.com>
> ---
>
> ...
>
> diff --git a/include/linux/pm_qos.h b/include/linux/pm_qos.h
> index 9105f47f5195..5193915913fe 100644
> --- a/include/linux/pm_qos.h
> +++ b/include/linux/pm_qos.h
> @@ -32,10 +32,12 @@ enum pm_qos_flags_status {
>  #define PM_QOS_CPU_DMA_LAT_DEFAULT_VALUE	(2000 * USEC_PER_SEC)
>  #define PM_QOS_RESUME_LATENCY_DEFAULT_VALUE	PM_QOS_LATENCY_ANY
>  #define PM_QOS_RESUME_LATENCY_NO_CONSTRAINT	PM_QOS_LATENCY_ANY
>  #define PM_QOS_RESUME_LATENCY_NO_CONSTRAINT_NS	PM_QOS_LATENCY_ANY_NS
>  #define PM_QOS_LATENCY_TOLERANCE_DEFAULT_VALUE	0
> +#define PM_QOS_MIN_FREQUENCY_DEFAULT_VALUE	0
> +#define PM_QOS_MAX_FREQUENCY_DEFAULT_VALUE	(-1)

The value of -1 is problematic, as reported on
https://patchwork.kernel.org/patch/11252413/#23017003.

dev_pm_qos_read_value(dev, DEV_PM_QOS_MAX_FREQUENCY) returns the smallest
value of all requests, which is PM_QOS_MAX_FREQUENCY_DEFAULT_VALUE / -1
unless all requests have set an actual constraint.

I'd suggest to change the default max value to S32_MAX or similar.