linux-kernel - [PATCH v1] ACPI: PM: s2idle: Add module parameter for LPS0 constraints checking

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Message-ID: <2827214.mvXUDI8C0e@rafael.j.wysocki>
Date: Tue, 13 Jan 2026 14:36:54 +0100
From: "Rafael J. Wysocki" <rafael@...nel.org>
To: Linux ACPI <linux-acpi@...r.kernel.org>
Cc: LKML <linux-kernel@...r.kernel.org>, Linux PM <linux-pm@...r.kernel.org>,
 Mario Limonciello <mario.limonciello@....com>,
 Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>
Subject:
 [PATCH v1] ACPI: PM: s2idle: Add module parameter for LPS0 constraints
 checking

From: Rafael J. Wysocki <rafael.j.wysocki@...el.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@...el.com>
---
 drivers/acpi/x86/s2idle.c |    8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

--- 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_han

 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
 	if (!lps0_device_handle || sleep_no_lps0)
 		return 0;

-	if (pm_debug_messages_on)
+	if (check_lps0_constraints)
 		lpi_check_constraints();

 	/* Screen off */