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Wysocki wrote: > On Tue, Jan 13, 2026 at 10:48 PM Mario Limonciello > wrote: >> On 1/13/2026 7:36 AM, Rafael J. Wysocki wrote: >>> From: Rafael J. Wysocki >>> >>> 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. >> >> Any ideas why it's causing problems? AML doing something it shouldn't? > > It's not a clear AML bug AFAICS. Rather, it seems to have > dependencies on something that is not ready when it is evaluated, so > an ordering issue or similar. Ah I see. > >>> >>> 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 >>> --- >>> 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"); >> >> I'm personally not really a fan of another module parameter for >> debugging. I know some other subsystem maintainers are very anti-module >> parameters too. >> >> I did like having /sys/power/pm_debug_messages able to be a one stop >> shop for debugging messages at runtime. > > Well, this is not just debug messages, rather a whole debug facility > enabled via pm_debug_messages, which is kind of confusing. Good point. > >> So I had another idea I wanted to throw around. What if instead we had >> a file /sys/kernel/debug/x86/lps0_constraints? > > Then you cannot use this without debugfs. I mean; yeah. But it really is debugging and most distros have debugfs enabled by default these days don't they? > >> If the file is never accessed never evaluate constraints. If you read >> it once then you can get a dump of all the current constraints and any >> future suspends during that boot will also include constraints in the >> logs (IE call lpi_check_constraints()). > > So if it is not in debugfs, it would need to be in sysfs and then I > don't see much difference between it and a module param, honestly. > > I actually prefer the latter because it uses an existing infra. I agree if debugfs is decided to be out sysfs and module parameter are equal footing and then this patch makes sense.