Messages in this thread | | | From | "Rafael J. Wysocki" <> | Date | Wed, 13 Jul 2022 20:27:37 +0200 | Subject | Re: [PATCH v3 01/10] PM: suspend: Introduce `pm_suspend_preferred_s2idle` |
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On Tue, Jul 12, 2022 at 10:17 PM Limonciello, Mario <mario.limonciello@amd.com> wrote: > > On 7/12/2022 14:06, Rafael J. Wysocki wrote: > > 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. > > In "practice" it means that the system has been enabled for Modern > Standby in Windows. > > > > > 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. > > Within this series the intent is to see that the vendor meant the system > to be using Modern Standby on Windows (and implicitly Suspend To Idle on > Linux). > > With this I was trying to distinguish intent of the OEM between intent > of the user for helping to declare policy. Maybe the distinction of OEM > and user decision don't really matter though and "mem_sleep_current" is > better to use? I think in a lot of the cases that I outlined I think > that mem_sleep_current can drop right in instead of acpi_gbl_FADT.flags.
Checking ACPI_FADT_LOW_POWER_S0 is questionable in the majority of cases, because if S3 is not supported, that flag is in fact irrelevant, because Linux will allow suspend-to-idle to be used in that case regardless of it.
> If you would like I'm happy to do that and send a new series.
I need to look at the individual pieces of code that check ACPI_FADT_LOW_POWER_S0.
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