On Sat, 10 Jan 2026, Micha³ Grzelak wrote:
> From: "Rafael J. Wysocki" <rafael.j.wysocki@intel.com>
>
> Commit 32ece31db4df ("ACPI: PM: s2idle: Only retrieve constraints when
> needed") attempted to avoid useless evaluation of LPS0 _DSM Function 1
> in lps0_device_attach() because pm_debug_messages_on might never be set
> (and that is the case on production systems most of the time), but it
> turns out that LPS0 _DSM Function 1 is generally problematic on some
> platforms and causes suspend issues to occur when pm_debug_messages_on
> is set now.
>
> In Linux, LPS0 _DSM Function 1 is only useful for diagnostics and only
> in the cases when the system does not reach the deepest platform idle
> state during suspend-to-idle for some reason.  If such diagnostics is
> not necessary, evaluating it is a loss of time, so using it along with
> the other pm_debug_messages_on diagnostics is questionable because the
> latter is expected to be suitable for collecting debug information even
> during production use of system suspend.
>
> For this reason, add a module parameter called check_lps0_constraints
> to control whether or not the list of LPS0 constraints will be checked
> in acpi_s2idle_prepare_late_lps0() and so whether or not to evaluate
> LPS0 _DSM Function 1 (once) in acpi_s2idle_begin_lps0().
>
> Fixes: 32ece31db4df ("ACPI: PM: s2idle: Only retrieve constraints when needed")
> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

Signed-off-by: Micha³ Grzelak <michal.grzelak@intel.com>

> ---
> drivers/acpi/x86/s2idle.c | 8 ++++++--
> 1 file changed, 6 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/acpi/x86/s2idle.c b/drivers/acpi/x86/s2idle.c
> index 2a9edb53d5d4..cc3c83e4cc23 100644
> --- a/drivers/acpi/x86/s2idle.c
> +++ b/drivers/acpi/x86/s2idle.c
> @@ -28,6 +28,10 @@ static bool sleep_no_lps0 __read_mostly;
> module_param(sleep_no_lps0, bool, 0644);
> MODULE_PARM_DESC(sleep_no_lps0, "Do not use the special LPS0 device interface");
>
> +static bool check_lps0_constraints __read_mostly;
> +module_param(check_lps0_constraints, bool, 0644);
> +MODULE_PARM_DESC(check_lps0_constraints, "Check LPS0 device constraints");
> +
> static const struct acpi_device_id lps0_device_ids[] = {
> 	{"PNP0D80", },
> 	{"", },
> @@ -515,7 +519,7 @@ static struct acpi_scan_handler lps0_handler = {
>
> static int acpi_s2idle_begin_lps0(void)
> {
> -	if (lps0_device_handle && !sleep_no_lps0 && pm_debug_messages_on &&
> +	if (lps0_device_handle && !sleep_no_lps0 && check_lps0_constraints &&
> 	    !lpi_constraints_table) {
> 		if (acpi_s2idle_vendor_amd())
> 			lpi_device_get_constraints_amd();
> @@ -540,7 +544,7 @@ static int acpi_s2idle_prepare_late_lps0(void)
> 	if (!lps0_device_handle || sleep_no_lps0)
> 		return 0;
>
> -	if (pm_debug_messages_on)
> +	if (check_lps0_constraints)
> 		lpi_check_constraints();
>
> 	/* Screen off */
> -- 
> 2.45.2
>
>