Messages in this thread | | | From | "Rafael J. Wysocki" <> | Date | Tue, 12 Jul 2022 21:06:57 +0200 | Subject | Re: [PATCH v3 01/10] PM: suspend: Introduce `pm_suspend_preferred_s2idle` |
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On Fri, Jul 1, 2022 at 4:33 AM Mario Limonciello <mario.limonciello@amd.com> wrote: > > Many drivers in the kernel will check the FADT to determine if low > power idle is supported and use this information to set up a policy > decision in the driver. To abstract this information from drivers > introduce a new helper symbol that can indicate this information. > > Signed-off-by: Mario Limonciello <mario.limonciello@amd.com> > --- > include/linux/suspend.h | 1 + > kernel/power/suspend.c | 17 +++++++++++++++++ > 2 files changed, 18 insertions(+) > > diff --git a/include/linux/suspend.h b/include/linux/suspend.h > index 70f2921e2e70..9d911e026720 100644 > --- a/include/linux/suspend.h > +++ b/include/linux/suspend.h > @@ -305,6 +305,7 @@ static inline bool idle_should_enter_s2idle(void) > return unlikely(s2idle_state == S2IDLE_STATE_ENTER); > } > > +extern bool pm_suspend_preferred_s2idle(void); > extern bool pm_suspend_default_s2idle(void); > extern void __init pm_states_init(void); > extern void s2idle_set_ops(const struct platform_s2idle_ops *ops); > diff --git a/kernel/power/suspend.c b/kernel/power/suspend.c > index 827075944d28..0030e7dfe6cf 100644 > --- a/kernel/power/suspend.c > +++ b/kernel/power/suspend.c > @@ -9,6 +9,7 @@ > > #define pr_fmt(fmt) "PM: " fmt > > +#include <linux/acpi.h> > #include <linux/string.h> > #include <linux/delay.h> > #include <linux/errno.h> > @@ -61,6 +62,22 @@ static DECLARE_SWAIT_QUEUE_HEAD(s2idle_wait_head); > enum s2idle_states __read_mostly s2idle_state; > static DEFINE_RAW_SPINLOCK(s2idle_lock); > > +/** > + * pm_suspend_preferred_s2idle - Check if suspend-to-idle is the preferred suspend method. > + * > + * Return 'true' if suspend-to-idle is preferred by the system designer for the default > + * suspend method. > + */ > +bool pm_suspend_preferred_s2idle(void) > +{ > +#ifdef CONFIG_ACPI > + return acpi_gbl_FADT.flags & ACPI_FADT_LOW_POWER_S0; > +#else > + return false; > +#endif > +} > +EXPORT_SYMBOL_GPL(pm_suspend_preferred_s2idle);
First, this is ACPI-specific, so please don't try to generalize it artificially. This confuses things and doesn't really help.
Second, ACPI_FADT_LOW_POWER_S0 means that "low power S0 idle" is supported, not that suspend-to-idle is the preferred suspend method in Linux.
System designers who set that bit in FADT may not even know what suspend-to-idle is.
But it is good that you have identified the code checking that bit, because it should not be checked without a valid reason. I need to review that code and see what's going on in there.
> + > /** > * pm_suspend_default_s2idle - Check if suspend-to-idle is the default suspend. > * > -- > 2.34.1 >
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