On Tue, Jul 8, 2025 at 4:28 PM Tudor Ambarus <tudor.ambarus@xxxxxxxxxx> wrote: > > On some platforms, device dependencies are not properly represented by > device links, which can cause issues when asynchronous power management > is enabled. While it is possible to disable this via sysfs, doing so > at runtime can race with the first system suspend event. > > This patch introduces a kernel command-line parameter, "pm_async", which > can be set to "off" to globally disable asynchronous suspend and resume > operations from early boot. This provides a robust way to fall back to > synchronous (sequential) operation, which can stabilize platforms with > problematic dependencies and also serve as a useful debugging tool. > > The default behavior remains unchanged (asynchronous enabled). To disable > it, boot the kernel with the "pm_async=off" parameter. IIUC, this effectively is a way to change the initial value of the existing pm_async sysfs knob. Might be worth mentioning in the changelog. > Signed-off-by: Tudor Ambarus <tudor.ambarus@xxxxxxxxxx> > --- > Dealing with the pixel6 downstream drivers to cope with the changes from > https://lore.kernel.org/linux-pm/10629535.nUPlyArG6x@xxxxxxxxxxxxx/. > > Similar to what people already reported it seems pixel6 lacks proper > device links dependencies downstream causing i2c and spi client drivers > to fail to suspend. Add kernel param to disable async suspend/resume. > --- > Documentation/admin-guide/kernel-parameters.txt | 9 +++++++++ > kernel/power/main.c | 9 +++++++++ > 2 files changed, 18 insertions(+) > > diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt > index f1f2c0874da9ddfc95058c464fdf5dabaf0de713..55ba3e747d86c09a0696e105a1d9cd99218f0c07 100644 > --- a/Documentation/admin-guide/kernel-parameters.txt > +++ b/Documentation/admin-guide/kernel-parameters.txt > @@ -5000,6 +5000,15 @@ > that number, otherwise (e.g., 'pmu_override=on'), MMCR1 > remains 0. > > + pm_async [PM] > + If set to "off", disables asynchronous suspend and > + resume of devices during system-wide power transitions. > + This can be useful on platforms where device > + dependencies are not well-defined, or for debugging > + power management issues. Defaults to "on" (asynchronous > + operations enabled). And here too because it is now unclear how this relates to the pm_sync under /sys/power/. > + > + > pm_debug_messages [SUSPEND,KNL] > Enable suspend/resume debug messages during boot up. > > diff --git a/kernel/power/main.c b/kernel/power/main.c > index 3d484630505ae91fea29f7f9b3fbcf7e585955d8..3cf2d7e72567ecbea2cd80acd3c7f6da85f5bef4 100644 > --- a/kernel/power/main.c > +++ b/kernel/power/main.c > @@ -8,6 +8,7 @@ > > #include <linux/acpi.h> > #include <linux/export.h> > +#include <linux/init.h> > #include <linux/kobject.h> > #include <linux/string.h> > #include <linux/pm-trace.h> > @@ -112,6 +113,14 @@ int pm_notifier_call_chain(unsigned long val) > /* If set, devices may be suspended and resumed asynchronously. */ > int pm_async_enabled = 1; > > +static int __init pm_async_setup(char *str) > +{ > + if (!strcmp(str, "off")) > + pm_async_enabled = 0; > + return 1; > +} > +__setup("pm_async=", pm_async_setup); > + > static ssize_t pm_async_show(struct kobject *kobj, struct kobj_attribute *attr, > char *buf) > { > > ---
