Re: [PATCH v3] PM: add kernel parameter to disable asynchronous suspend/resume

[Tudor Ambarus <tudor.ambarus@linaro.org>]

On 7/9/25 1:31 PM, Tudor Ambarus 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. It effectively provides a way to set the
> initial value of the existing pm_async sysfs knob at boot time. This
> offers a robust method 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.
> 
> Signed-off-by: Tudor Ambarus <tudor.ambarus@linaro.org>
> ---
> Dealing with the pixel6 downstream drivers to cope with the changes from
> https://lore.kernel.org/linux-pm/10629535.nUPlyArG6x@rjwysocki.net/.
> 
> 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.
> ---
> Changes in v3:
> - update documentation with "pm_async=" and "Format: off" (Randy)
> - reword documentation to make it clear "on" isn't a selectable option
>   for pm_async because it's the default behavior.
> - Link to v2: https://lore.kernel.org/r/20250708-pm-async-off-v2-1-7fada54f01c0@linaro.org
> 
> Changes in v2:
> - update the documentation and the commit message to describe that the
>   "pm_async" kernel parameter provides a way to change the initial value
>   of the existing /sys/power/pm_async sysfs knob.
> - Link to v1: https://lore.kernel.org/r/20250708-pm-async-off-v1-1-1b200cc03d9c@linaro.org
> ---
>  Documentation/admin-guide/kernel-parameters.txt | 12 ++++++++++++
>  kernel/power/main.c                             |  9 +++++++++
>  2 files changed, 21 insertions(+)
> 
> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> index f1f2c0874da9ddfc95058c464fdf5dabaf0de713..06beacf208de3242a3b4bb2413ab6cd3e0083f15 100644
> --- a/Documentation/admin-guide/kernel-parameters.txt
> +++ b/Documentation/admin-guide/kernel-parameters.txt
> @@ -5000,6 +5000,18 @@
>  			that number, otherwise (e.g., 'pmu_override=on'), MMCR1
>  			remains 0.
>  
> +	pm_async=	[PM]
> +			Format: off
> +			This parameter sets the initial value of the
> +			/sys/power/pm_async sysfs knob at boot time.
> +			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. Asynchronous operations are
> +			enabled by default.
> +
> +

I just noticed an extra new line here, that checkpatch didn't catch.
Please let me know if I have to resubmit, or it can be amended
when/if applied.

Cheers,
ta