On Mon, 30 Nov 2020 at 23:51, Lina Iyer <ilina@xxxxxxxxxxxxxx> wrote:
>
> Some devices may have a predictable interrupt pattern while executing
> usecases. An example would be the VSYNC interrupt associated with
> display devices. A 60 Hz display could cause a interrupt every 16 ms. If
> the device were in a PM domain, the domain would need to be powered up
> for device to resume and handle the interrupt.
>
> Entering a domain idle state saves power, only if the residency of the
> idle state is met. Without knowing the idle duration of the domain, the
> governor would just choose the deepest idle state that matches the QoS
> requirements. The domain might be powered off just as the device is
> expecting to wake up. If devices could inform PM frameworks of their
> next event, the parent PM domain's idle duration can be determined.
>
> So let's add the dev_pm_genpd_set_next_wakeup() API for the device to
> inform PM domains of the impending wakeup. This information will be the
> domain governor to determine the best idle state given the wakeup.
>
> Signed-off-by: Lina Iyer <ilina@xxxxxxxxxxxxxx>
> ---
> Changes in v6:
> - Update documentation
> Changes in v5:
> - Fix commit text as pointed by Ulf
> - Use -EOPNOTSUPP
> Changes in v4:
> - Use PM domain data to store next_wakeup
> - Drop runtime PM documentation
> Changes in v3:
> - Fix unwanted change
> Changes in v2:
> - Update documentation
> - Remove runtime PM enabled check
> - Update commit text
> ---
> drivers/base/power/domain.c | 41 +++++++++++++++++++++++++++++++++++++
> include/linux/pm_domain.h | 8 ++++++++
> 2 files changed, 49 insertions(+)
>
> diff --git a/drivers/base/power/domain.c b/drivers/base/power/domain.c
> index 1e6c0bf1c945..191539a8e06d 100644
> --- a/drivers/base/power/domain.c
> +++ b/drivers/base/power/domain.c
> @@ -408,6 +408,46 @@ int dev_pm_genpd_set_performance_state(struct device *dev, unsigned int state)
> }
> EXPORT_SYMBOL_GPL(dev_pm_genpd_set_performance_state);
>
> +/**
> + * dev_pm_genpd_set_next_wakeup - Notify PM framework of an impending wakeup.
> + *
> + * @dev: Device to handle
> + * @next: impending interrupt/wakeup for the device
> + *
> + * Allow devices to inform of the next wakeup. But, if the domain were already
> + * powered off, we will not wakeup the domain to recompute it's idle duration.
How about clarifying this as:
"It's assumed that the users guarantee that the genpd wouldn't be
detached while this routine is getting called. Additionally, it's also
assumed that @dev isn't runtime suspended (RPM_SUSPENDED).
> + * Although devices are expected to update the next_wakeup after the end of
> + * their usecase as well, it is possible the devices themselves may not know
> + * about that. Stale @next will be ignored when powering off the domain.
> + */
> +int dev_pm_genpd_set_next_wakeup(struct device *dev, ktime_t next)
> +{
> + struct generic_pm_domain *genpd;
> + struct generic_pm_domain_data *gpd_data;
> + int ret = -EINVAL;
> +
> + genpd = dev_to_genpd_safe(dev);
> + if (!genpd)
> + return -ENODEV;
> +
> + if (WARN_ON(!dev->power.subsys_data ||
> + !dev->power.subsys_data->domain_data))
> + return ret;
> +
> + genpd_lock(genpd);
> + gpd_data = to_gpd_data(dev->power.subsys_data->domain_data);
> + if (ktime_before(ktime_get(), next)) {
> + gpd_data->next_wakeup = next;
> + genpd->flags |= GENPD_FLAG_GOV_NEXT_WAKEUP;
I don't think we should set this here, but instead leave this to be
set by the genpd provider at initialization.
> + ret = 0;
> + }
> + genpd_unlock(genpd);
I would suggest to simplify the above into:
gpd_data = to_gpd_data(dev->power.subsys_data->domain_data);
gpd_data->next_wakeup = next;
Then there is no need for locks because:
*) We assume the device remains attached to the genpd.
**) The device isn't runtime suspended, hence its corresponding genpd
is powered on and thus the genpd governor can't be looking at
"gpd_data->next_wakeup" simulantfsfulsy.
Moreover, as we agreed to ignore stale values for "next", there is no
reason to validate it against the current ktime, so let's just skip
it.
> +
> + return ret;
> +}
> +EXPORT_SYMBOL_GPL(dev_pm_genpd_set_next_wakeup);
> +
> +
> static int _genpd_power_on(struct generic_pm_domain *genpd, bool timed)
> {
> unsigned int state_idx = genpd->state_idx;
> @@ -1450,6 +1490,7 @@ static struct generic_pm_domain_data *genpd_alloc_dev_data(struct device *dev)
> gpd_data->td.constraint_changed = true;
> gpd_data->td.effective_constraint_ns = PM_QOS_RESUME_LATENCY_NO_CONSTRAINT_NS;
> gpd_data->nb.notifier_call = genpd_dev_pm_qos_notifier;
> + gpd_data->next_wakeup = KTIME_MAX;
When looking at patch3, I wonder if it perhaps could be easier to use
"zero" as the default value? What do you think, just an idea?
>
> spin_lock_irq(&dev->power.lock);
>
> diff --git a/include/linux/pm_domain.h b/include/linux/pm_domain.h
> index 1f359bd19f77..cc27d3d88849 100644
> --- a/include/linux/pm_domain.h
> +++ b/include/linux/pm_domain.h
> @@ -9,6 +9,7 @@
> #define _LINUX_PM_DOMAIN_H
>
> #include <linux/device.h>
> +#include <linux/ktime.h>
> #include <linux/mutex.h>
> #include <linux/pm.h>
> #include <linux/err.h>
> @@ -197,6 +198,7 @@ struct generic_pm_domain_data {
> struct notifier_block *power_nb;
> int cpu;
> unsigned int performance_state;
> + ktime_t next_wakeup;
> void *data;
> };
>
> @@ -229,6 +231,7 @@ int dev_pm_genpd_set_performance_state(struct device *dev, unsigned int state);
> int dev_pm_genpd_add_notifier(struct device *dev, struct notifier_block *nb);
> int dev_pm_genpd_remove_notifier(struct device *dev);
> void genpd_enable_next_wakeup(struct generic_pm_domain *genpd, bool enable);
> +int dev_pm_genpd_set_next_wakeup(struct device *dev, ktime_t next);
>
> extern struct dev_power_governor simple_qos_governor;
> extern struct dev_power_governor pm_domain_always_on_gov;
> @@ -291,6 +294,11 @@ static void genpd_enable_next_wakeup(struct generic_pm_domain *genpd,
> bool enable)
> { }
>
> +static inline int dev_pm_genpd_set_next_wakeup(struct device *dev, ktime_t next)
> +{
> + return -EOPNOTSUPP;
> +}
> +
> #define simple_qos_governor (*(struct dev_power_governor *)(NULL))
> #define pm_domain_always_on_gov (*(struct dev_power_governor *)(NULL))
> #endif
> --
> The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum,
> a Linux Foundation Collaborative Project
>
Kind regards
Uffe
